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Diffstat (limited to 'drivers/lguest/page_tables.c')
| -rw-r--r-- | drivers/lguest/page_tables.c | 735 |
1 files changed, 735 insertions, 0 deletions
diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c new file mode 100644 index 0000000..81d0c60 --- /dev/null +++ b/drivers/lguest/page_tables.c @@ -0,0 +1,735 @@ +/*P:700 The pagetable code, on the other hand, still shows the scars of + * previous encounters. It's functional, and as neat as it can be in the + * circumstances, but be wary, for these things are subtle and break easily. + * The Guest provides a virtual to physical mapping, but we can neither trust + * it nor use it: we verify and convert it here then point the CPU to the + * converted Guest pages when running the Guest. :*/ + +/* Copyright (C) Rusty Russell IBM Corporation 2006. + * GPL v2 and any later version */ +#include <linux/mm.h> +#include <linux/types.h> +#include <linux/spinlock.h> +#include <linux/random.h> +#include <linux/percpu.h> +#include <asm/tlbflush.h> +#include <asm/uaccess.h> +#include "lg.h" + +/*M:008 We hold reference to pages, which prevents them from being swapped. + * It'd be nice to have a callback in the "struct mm_struct" when Linux wants + * to swap out. If we had this, and a shrinker callback to trim PTE pages, we + * could probably consider launching Guests as non-root. :*/ + +/*H:300 + * The Page Table Code + * + * We use two-level page tables for the Guest. If you're not entirely + * comfortable with virtual addresses, physical addresses and page tables then + * I recommend you review arch/x86/lguest/boot.c's "Page Table Handling" (with + * diagrams!). + * + * The Guest keeps page tables, but we maintain the actual ones here: these are + * called "shadow" page tables. Which is a very Guest-centric name: these are + * the real page tables the CPU uses, although we keep them up to date to + * reflect the Guest's. (See what I mean about weird naming? Since when do + * shadows reflect anything?) + * + * Anyway, this is the most complicated part of the Host code. There are seven + * parts to this: + * (i) Looking up a page table entry when the Guest faults, + * (ii) Making sure the Guest stack is mapped, + * (iii) Setting up a page table entry when the Guest tells us one has changed, + * (iv) Switching page tables, + * (v) Flushing (throwing away) page tables, + * (vi) Mapping the Switcher when the Guest is about to run, + * (vii) Setting up the page tables initially. + :*/ + + +/* 1024 entries in a page table page maps 1024 pages: 4MB. The Switcher is + * conveniently placed at the top 4MB, so it uses a separate, complete PTE + * page. */ +#define SWITCHER_PGD_INDEX (PTRS_PER_PGD - 1) + +/* We actually need a separate PTE page for each CPU. Remember that after the + * Switcher code itself comes two pages for each CPU, and we don't want this + * CPU's guest to see the pages of any other CPU. */ +static DEFINE_PER_CPU(pte_t *, switcher_pte_pages); +#define switcher_pte_page(cpu) per_cpu(switcher_pte_pages, cpu) + +/*H:320 The page table code is curly enough to need helper functions to keep it + * clear and clean. + * + * There are two functions which return pointers to the shadow (aka "real") + * page tables. + * + * spgd_addr() takes the virtual address and returns a pointer to the top-level + * page directory entry (PGD) for that address. Since we keep track of several + * page tables, the "i" argument tells us which one we're interested in (it's + * usually the current one). */ +static pgd_t *spgd_addr(struct lg_cpu *cpu, u32 i, unsigned long vaddr) +{ + unsigned int index = pgd_index(vaddr); + + /* We kill any Guest trying to touch the Switcher addresses. */ + if (index >= SWITCHER_PGD_INDEX) { + kill_guest(cpu, "attempt to access switcher pages"); + index = 0; + } + /* Return a pointer index'th pgd entry for the i'th page table. */ + return &cpu->lg->pgdirs[i].pgdir[index]; +} + +/* This routine then takes the page directory entry returned above, which + * contains the address of the page table entry (PTE) page. It then returns a + * pointer to the PTE entry for the given address. */ +static pte_t *spte_addr(pgd_t spgd, unsigned long vaddr) +{ + pte_t *page = __va(pgd_pfn(spgd) << PAGE_SHIFT); + /* You should never call this if the PGD entry wasn't valid */ + BUG_ON(!(pgd_flags(spgd) & _PAGE_PRESENT)); + return &page[(vaddr >> PAGE_SHIFT) % PTRS_PER_PTE]; +} + +/* These two functions just like the above two, except they access the Guest + * page tables. Hence they return a Guest address. */ +static unsigned long gpgd_addr(struct lg_cpu *cpu, unsigned long vaddr) +{ + unsigned int index = vaddr >> (PGDIR_SHIFT); + return cpu->lg->pgdirs[cpu->cpu_pgd].gpgdir + index * sizeof(pgd_t); +} + +static unsigned long gpte_addr(pgd_t gpgd, unsigned long vaddr) +{ + unsigned long gpage = pgd_pfn(gpgd) << PAGE_SHIFT; + BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT)); + return gpage + ((vaddr>>PAGE_SHIFT) % PTRS_PER_PTE) * sizeof(pte_t); +} +/*:*/ + +/*M:014 get_pfn is slow: we could probably try to grab batches of pages here as + * an optimization (ie. pre-faulting). :*/ + +/*H:350 This routine takes a page number given by the Guest and converts it to + * an actual, physical page number. It can fail for several reasons: the + * virtual address might not be mapped by the Launcher, the write flag is set + * and the page is read-only, or the write flag was set and the page was + * shared so had to be copied, but we ran out of memory. + * + * This holds a reference to the page, so release_pte() is careful to put that + * back. */ +static unsigned long get_pfn(unsigned long virtpfn, int write) +{ + struct page *page; + + /* gup me one page at this address please! */ + if (get_user_pages_fast(virtpfn << PAGE_SHIFT, 1, write, &page) == 1) + return page_to_pfn(page); + + /* This value indicates failure. */ + return -1UL; +} + +/*H:340 Converting a Guest page table entry to a shadow (ie. real) page table + * entry can be a little tricky. The flags are (almost) the same, but the + * Guest PTE contains a virtual page number: the CPU needs the real page + * number. */ +static pte_t gpte_to_spte(struct lg_cpu *cpu, pte_t gpte, int write) +{ + unsigned long pfn, base, flags; + + /* The Guest sets the global flag, because it thinks that it is using + * PGE. We only told it to use PGE so it would tell us whether it was + * flushing a kernel mapping or a userspace mapping. We don't actually + * use the global bit, so throw it away. */ + flags = (pte_flags(gpte) & ~_PAGE_GLOBAL); + + /* The Guest's pages are offset inside the Launcher. */ + base = (unsigned long)cpu->lg->mem_base / PAGE_SIZE; + + /* We need a temporary "unsigned long" variable to hold the answer from + * get_pfn(), because it returns 0xFFFFFFFF on failure, which wouldn't + * fit in spte.pfn. get_pfn() finds the real physical number of the + * page, given the virtual number. */ + pfn = get_pfn(base + pte_pfn(gpte), write); + if (pfn == -1UL) { + kill_guest(cpu, "failed to get page %lu", pte_pfn(gpte)); + /* When we destroy the Guest, we'll go through the shadow page + * tables and release_pte() them. Make sure we don't think + * this one is valid! */ + flags = 0; + } + /* Now we assemble our shadow PTE from the page number and flags. */ + return pfn_pte(pfn, __pgprot(flags)); +} + +/*H:460 And to complete the chain, release_pte() looks like this: */ +static void release_pte(pte_t pte) +{ + /* Remember that get_user_pages_fast() took a reference to the page, in + * get_pfn()? We have to put it back now. */ + if (pte_flags(pte) & _PAGE_PRESENT) + put_page(pfn_to_page(pte_pfn(pte))); +} +/*:*/ + +static void check_gpte(struct lg_cpu *cpu, pte_t gpte) +{ + if ((pte_flags(gpte) & _PAGE_PSE) || + pte_pfn(gpte) >= cpu->lg->pfn_limit) + kill_guest(cpu, "bad page table entry"); +} + +static void check_gpgd(struct lg_cpu *cpu, pgd_t gpgd) +{ + if ((pgd_flags(gpgd) & ~_PAGE_TABLE) || + (pgd_pfn(gpgd) >= cpu->lg->pfn_limit)) + kill_guest(cpu, "bad page directory entry"); +} + +/*H:330 + * (i) Looking up a page table entry when the Guest faults. + * + * We saw this call in run_guest(): when we see a page fault in the Guest, we + * come here. That's because we only set up the shadow page tables lazily as + * they're needed, so we get page faults all the time and quietly fix them up + * and return to the Guest without it knowing. + * + * If we fixed up the fault (ie. we mapped the address), this routine returns + * true. Otherwise, it was a real fault and we need to tell the Guest. */ +int demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode) +{ + pgd_t gpgd; + pgd_t *spgd; + unsigned long gpte_ptr; + pte_t gpte; + pte_t *spte; + + /* First step: get the top-level Guest page table entry. */ + gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t); + /* Toplevel not present? We can't map it in. */ + if (!(pgd_flags(gpgd) & _PAGE_PRESENT)) + return 0; + + /* Now look at the matching shadow entry. */ + spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr); + if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) { + /* No shadow entry: allocate a new shadow PTE page. */ + unsigned long ptepage = get_zeroed_page(GFP_KERNEL); + /* This is not really the Guest's fault, but killing it is + * simple for this corner case. */ + if (!ptepage) { + kill_guest(cpu, "out of memory allocating pte page"); + return 0; + } + /* We check that the Guest pgd is OK. */ + check_gpgd(cpu, gpgd); + /* And we copy the flags to the shadow PGD entry. The page + * number in the shadow PGD is the page we just allocated. */ + *spgd = __pgd(__pa(ptepage) | pgd_flags(gpgd)); + } + + /* OK, now we look at the lower level in the Guest page table: keep its + * address, because we might update it later. */ + gpte_ptr = gpte_addr(gpgd, vaddr); + gpte = lgread(cpu, gpte_ptr, pte_t); + + /* If this page isn't in the Guest page tables, we can't page it in. */ + if (!(pte_flags(gpte) & _PAGE_PRESENT)) + return 0; + + /* Check they're not trying to write to a page the Guest wants + * read-only (bit 2 of errcode == write). */ + if ((errcode & 2) && !(pte_flags(gpte) & _PAGE_RW)) + return 0; + + /* User access to a kernel-only page? (bit 3 == user access) */ + if ((errcode & 4) && !(pte_flags(gpte) & _PAGE_USER)) + return 0; + + /* Check that the Guest PTE flags are OK, and the page number is below + * the pfn_limit (ie. not mapping the Launcher binary). */ + check_gpte(cpu, gpte); + + /* Add the _PAGE_ACCESSED and (for a write) _PAGE_DIRTY flag */ + gpte = pte_mkyoung(gpte); + if (errcode & 2) + gpte = pte_mkdirty(gpte); + + /* Get the pointer to the shadow PTE entry we're going to set. */ + spte = spte_addr(*spgd, vaddr); + /* If there was a valid shadow PTE entry here before, we release it. + * This can happen with a write to a previously read-only entry. */ + release_pte(*spte); + + /* If this is a write, we insist that the Guest page is writable (the + * final arg to gpte_to_spte()). */ + if (pte_dirty(gpte)) + *spte = gpte_to_spte(cpu, gpte, 1); + else + /* If this is a read, don't set the "writable" bit in the page + * table entry, even if the Guest says it's writable. That way + * we will come back here when a write does actually occur, so + * we can update the Guest's _PAGE_DIRTY flag. */ + *spte = gpte_to_spte(cpu, pte_wrprotect(gpte), 0); + + /* Finally, we write the Guest PTE entry back: we've set the + * _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags. */ + lgwrite(cpu, gpte_ptr, pte_t, gpte); + + /* The fault is fixed, the page table is populated, the mapping + * manipulated, the result returned and the code complete. A small + * delay and a trace of alliteration are the only indications the Guest + * has that a page fault occurred at all. */ + return 1; +} + +/*H:360 + * (ii) Making sure the Guest stack is mapped. + * + * Remember that direct traps into the Guest need a mapped Guest kernel stack. + * pin_stack_pages() calls us here: we could simply call demand_page(), but as + * we've seen that logic is quite long, and usually the stack pages are already + * mapped, so it's overkill. + * + * This is a quick version which answers the question: is this virtual address + * mapped by the shadow page tables, and is it writable? */ +static int page_writable(struct lg_cpu *cpu, unsigned long vaddr) +{ + pgd_t *spgd; + unsigned long flags; + + /* Look at the current top level entry: is it present? */ + spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr); + if (!(pgd_flags(*spgd) & _PAGE_PRESENT)) + return 0; + + /* Check the flags on the pte entry itself: it must be present and + * writable. */ + flags = pte_flags(*(spte_addr(*spgd, vaddr))); + + return (flags & (_PAGE_PRESENT|_PAGE_RW)) == (_PAGE_PRESENT|_PAGE_RW); +} + +/* So, when pin_stack_pages() asks us to pin a page, we check if it's already + * in the page tables, and if not, we call demand_page() with error code 2 + * (meaning "write"). */ +void pin_page(struct lg_cpu *cpu, unsigned long vaddr) +{ + if (!page_writable(cpu, vaddr) && !demand_page(cpu, vaddr, 2)) + kill_guest(cpu, "bad stack page %#lx", vaddr); +} + +/*H:450 If we chase down the release_pgd() code, it looks like this: */ +static void release_pgd(struct lguest *lg, pgd_t *spgd) +{ + /* If the entry's not present, there's nothing to release. */ + if (pgd_flags(*spgd) & _PAGE_PRESENT) { + unsigned int i; + /* Converting the pfn to find the actual PTE page is easy: turn + * the page number into a physical address, then convert to a + * virtual address (easy for kernel pages like this one). */ + pte_t *ptepage = __va(pgd_pfn(*spgd) << PAGE_SHIFT); + /* For each entry in the page, we might need to release it. */ + for (i = 0; i < PTRS_PER_PTE; i++) + release_pte(ptepage[i]); + /* Now we can free the page of PTEs */ + free_page((long)ptepage); + /* And zero out the PGD entry so we never release it twice. */ + *spgd = __pgd(0); + } +} + +/*H:445 We saw flush_user_mappings() twice: once from the flush_user_mappings() + * hypercall and once in new_pgdir() when we re-used a top-level pgdir page. + * It simply releases every PTE page from 0 up to the Guest's kernel address. */ +static void flush_user_mappings(struct lguest *lg, int idx) +{ + unsigned int i; + /* Release every pgd entry up to the kernel's address. */ + for (i = 0; i < pgd_index(lg->kernel_address); i++) + release_pgd(lg, lg->pgdirs[idx].pgdir + i); +} + +/*H:440 (v) Flushing (throwing away) page tables, + * + * The Guest has a hypercall to throw away the page tables: it's used when a + * large number of mappings have been changed. */ +void guest_pagetable_flush_user(struct lg_cpu *cpu) +{ + /* Drop the userspace part of the current page table. */ + flush_user_mappings(cpu->lg, cpu->cpu_pgd); +} +/*:*/ + +/* We walk down the guest page tables to get a guest-physical address */ +unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr) +{ + pgd_t gpgd; + pte_t gpte; + + /* First step: get the top-level Guest page table entry. */ + gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t); + /* Toplevel not present? We can't map it in. */ + if (!(pgd_flags(gpgd) & _PAGE_PRESENT)) + kill_guest(cpu, "Bad address %#lx", vaddr); + + gpte = lgread(cpu, gpte_addr(gpgd, vaddr), pte_t); + if (!(pte_flags(gpte) & _PAGE_PRESENT)) + kill_guest(cpu, "Bad address %#lx", vaddr); + + return pte_pfn(gpte) * PAGE_SIZE | (vaddr & ~PAGE_MASK); +} + +/* We keep several page tables. This is a simple routine to find the page + * table (if any) corresponding to this top-level address the Guest has given + * us. */ +static unsigned int find_pgdir(struct lguest *lg, unsigned long pgtable) +{ + unsigned int i; + for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) + if (lg->pgdirs[i].pgdir && lg->pgdirs[i].gpgdir == pgtable) + break; + return i; +} + +/*H:435 And this is us, creating the new page directory. If we really do + * allocate a new one (and so the kernel parts are not there), we set + * blank_pgdir. */ +static unsigned int new_pgdir(struct lg_cpu *cpu, + unsigned long gpgdir, + int *blank_pgdir) +{ + unsigned int next; + + /* We pick one entry at random to throw out. Choosing the Least + * Recently Used might be better, but this is easy. */ + next = random32() % ARRAY_SIZE(cpu->lg->pgdirs); + /* If it's never been allocated at all before, try now. */ + if (!cpu->lg->pgdirs[next].pgdir) { + cpu->lg->pgdirs[next].pgdir = + (pgd_t *)get_zeroed_page(GFP_KERNEL); + /* If the allocation fails, just keep using the one we have */ + if (!cpu->lg->pgdirs[next].pgdir) + next = cpu->cpu_pgd; + else + /* This is a blank page, so there are no kernel + * mappings: caller must map the stack! */ + *blank_pgdir = 1; + } + /* Record which Guest toplevel this shadows. */ + cpu->lg->pgdirs[next].gpgdir = gpgdir; + /* Release all the non-kernel mappings. */ + flush_user_mappings(cpu->lg, next); + + return next; +} + +/*H:430 (iv) Switching page tables + * + * Now we've seen all the page table setting and manipulation, let's see what + * what happens when the Guest changes page tables (ie. changes the top-level + * pgdir). This occurs on almost every context switch. */ +void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable) +{ + int newpgdir, repin = 0; + + /* Look to see if we have this one already. */ + newpgdir = find_pgdir(cpu->lg, pgtable); + /* If not, we allocate or mug an existing one: if it's a fresh one, + * repin gets set to 1. */ + if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs)) + newpgdir = new_pgdir(cpu, pgtable, &repin); + /* Change the current pgd index to the new one. */ + cpu->cpu_pgd = newpgdir; + /* If it was completely blank, we map in the Guest kernel stack */ + if (repin) + pin_stack_pages(cpu); +} + +/*H:470 Finally, a routine which throws away everything: all PGD entries in all + * the shadow page tables, including the Guest's kernel mappings. This is used + * when we destroy the Guest. */ +static void release_all_pagetables(struct lguest *lg) +{ + unsigned int i, j; + + /* Every shadow pagetable this Guest has */ + for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) + if (lg->pgdirs[i].pgdir) + /* Every PGD entry except the Switcher at the top */ + for (j = 0; j < SWITCHER_PGD_INDEX; j++) + release_pgd(lg, lg->pgdirs[i].pgdir + j); +} + +/* We also throw away everything when a Guest tells us it's changed a kernel + * mapping. Since kernel mappings are in every page table, it's easiest to + * throw them all away. This traps the Guest in amber for a while as + * everything faults back in, but it's rare. */ +void guest_pagetable_clear_all(struct lg_cpu *cpu) +{ + release_all_pagetables(cpu->lg); + /* We need the Guest kernel stack mapped again. */ + pin_stack_pages(cpu); +} +/*:*/ +/*M:009 Since we throw away all mappings when a kernel mapping changes, our + * performance sucks for guests using highmem. In fact, a guest with + * PAGE_OFFSET 0xc0000000 (the default) and more than about 700MB of RAM is + * usually slower than a Guest with less memory. + * + * This, of course, cannot be fixed. It would take some kind of... well, I + * don't know, but the term "puissant code-fu" comes to mind. :*/ + +/*H:420 This is the routine which actually sets the page table entry for then + * "idx"'th shadow page table. + * + * Normally, we can just throw out the old entry and replace it with 0: if they + * use it demand_page() will put the new entry in. We need to do this anyway: + * The Guest expects _PAGE_ACCESSED to be set on its PTE the first time a page + * is read from, and _PAGE_DIRTY when it's written to. + * + * But Avi Kivity pointed out that most Operating Systems (Linux included) set + * these bits on PTEs immediately anyway. This is done to save the CPU from + * having to update them, but it helps us the same way: if they set + * _PAGE_ACCESSED then we can put a read-only PTE entry in immediately, and if + * they set _PAGE_DIRTY then we can put a writable PTE entry in immediately. + */ +static void do_set_pte(struct lg_cpu *cpu, int idx, + unsigned long vaddr, pte_t gpte) +{ + /* Look up the matching shadow page directory entry. */ + pgd_t *spgd = spgd_addr(cpu, idx, vaddr); + + /* If the top level isn't present, there's no entry to update. */ + if (pgd_flags(*spgd) & _PAGE_PRESENT) { + /* Otherwise, we start by releasing the existing entry. */ + pte_t *spte = spte_addr(*spgd, vaddr); + release_pte(*spte); + + /* If they're setting this entry as dirty or accessed, we might + * as well put that entry they've given us in now. This shaves + * 10% off a copy-on-write micro-benchmark. */ + if (pte_flags(gpte) & (_PAGE_DIRTY | _PAGE_ACCESSED)) { + check_gpte(cpu, gpte); + *spte = gpte_to_spte(cpu, gpte, + pte_flags(gpte) & _PAGE_DIRTY); + } else + /* Otherwise kill it and we can demand_page() it in + * later. */ + *spte = __pte(0); + } +} + +/*H:410 Updating a PTE entry is a little trickier. + * + * We keep track of several different page tables (the Guest uses one for each + * process, so it makes sense to cache at least a few). Each of these have + * identical kernel parts: ie. every mapping above PAGE_OFFSET is the same for + * all processes. So when the page table above that address changes, we update + * all the page tables, not just the current one. This is rare. + * + * The benefit is that when we have to track a new page table, we can keep all + * the kernel mappings. This speeds up context switch immensely. */ +void guest_set_pte(struct lg_cpu *cpu, + unsigned long gpgdir, unsigned long vaddr, pte_t gpte) +{ + /* Kernel mappings must be changed on all top levels. Slow, but doesn't + * happen often. */ + if (vaddr >= cpu->lg->kernel_address) { + unsigned int i; + for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++) + if (cpu->lg->pgdirs[i].pgdir) + do_set_pte(cpu, i, vaddr, gpte); + } else { + /* Is this page table one we have a shadow for? */ + int pgdir = find_pgdir(cpu->lg, gpgdir); + if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs)) + /* If so, do the update. */ + do_set_pte(cpu, pgdir, vaddr, gpte); + } +} + +/*H:400 + * (iii) Setting up a page table entry when the Guest tells us one has changed. + * + * Just like we did in interrupts_and_traps.c, it makes sense for us to deal + * with the other side of page tables while we're here: what happens when the + * Guest asks for a page table to be updated? + * + * We already saw that demand_page() will fill in the shadow page tables when + * needed, so we can simply remove shadow page table entries whenever the Guest + * tells us they've changed. When the Guest tries to use the new entry it will + * fault and demand_page() will fix it up. + * + * So with that in mind here's our code to to update a (top-level) PGD entry: + */ +void guest_set_pmd(struct lguest *lg, unsigned long gpgdir, u32 idx) +{ + int pgdir; + + /* The kernel seems to try to initialize this early on: we ignore its + * attempts to map over the Switcher. */ + if (idx >= SWITCHER_PGD_INDEX) + return; + + /* If they're talking about a page table we have a shadow for... */ + pgdir = find_pgdir(lg, gpgdir); + if (pgdir < ARRAY_SIZE(lg->pgdirs)) + /* ... throw it away. */ + release_pgd(lg, lg->pgdirs[pgdir].pgdir + idx); +} + +/*H:500 (vii) Setting up the page tables initially. + * + * When a Guest is first created, the Launcher tells us where the toplevel of + * its first page table is. We set some things up here: */ +int init_guest_pagetable(struct lguest *lg, unsigned long pgtable) +{ + /* We start on the first shadow page table, and give it a blank PGD + * page. */ + lg->pgdirs[0].gpgdir = pgtable; + lg->pgdirs[0].pgdir = (pgd_t *)get_zeroed_page(GFP_KERNEL); + if (!lg->pgdirs[0].pgdir) + return -ENOMEM; + lg->cpus[0].cpu_pgd = 0; + return 0; +} + +/* When the Guest calls LHCALL_LGUEST_INIT we do more setup. */ +void page_table_guest_data_init(struct lg_cpu *cpu) +{ + /* We get the kernel address: above this is all kernel memory. */ + if (get_user(cpu->lg->kernel_address, + &cpu->lg->lguest_data->kernel_address) + /* We tell the Guest that it can't use the top 4MB of virtual + * addresses used by the Switcher. */ + || put_user(4U*1024*1024, &cpu->lg->lguest_data->reserve_mem) + || put_user(cpu->lg->pgdirs[0].gpgdir, &cpu->lg->lguest_data->pgdir)) + kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data); + + /* In flush_user_mappings() we loop from 0 to + * "pgd_index(lg->kernel_address)". This assumes it won't hit the + * Switcher mappings, so check that now. */ + if (pgd_index(cpu->lg->kernel_address) >= SWITCHER_PGD_INDEX) + kill_guest(cpu, "bad kernel address %#lx", + cpu->lg->kernel_address); +} + +/* When a Guest dies, our cleanup is fairly simple. */ +void free_guest_pagetable(struct lguest *lg) +{ + unsigned int i; + + /* Throw away all page table pages. */ + release_all_pagetables(lg); + /* Now free the top levels: free_page() can handle 0 just fine. */ + for (i = 0; i < ARRAY_SIZE(lg->pgdirs); i++) + free_page((long)lg->pgdirs[i].pgdir); +} + +/*H:480 (vi) Mapping the Switcher when the Guest is about to run. + * + * The Switcher and the two pages for this CPU need to be visible in the + * Guest (and not the pages for other CPUs). We have the appropriate PTE pages + * for each CPU already set up, we just need to hook them in now we know which + * Guest is about to run on this CPU. */ +void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages) +{ + pte_t *switcher_pte_page = __get_cpu_var(switcher_pte_pages); + pgd_t switcher_pgd; + pte_t regs_pte; + unsigned long pfn; + + /* Make the last PGD entry for this Guest point to the Switcher's PTE + * page for this CPU (with appropriate flags). */ + switcher_pgd = __pgd(__pa(switcher_pte_page) | __PAGE_KERNEL); + + cpu->lg->pgdirs[cpu->cpu_pgd].pgdir[SWITCHER_PGD_INDEX] = switcher_pgd; + + /* We also change the Switcher PTE page. When we're running the Guest, + * we want the Guest's "regs" page to appear where the first Switcher + * page for this CPU is. This is an optimization: when the Switcher + * saves the Guest registers, it saves them into the first page of this + * CPU's "struct lguest_pages": if we make sure the Guest's register + * page is already mapped there, we don't have to copy them out + * again. */ + pfn = __pa(cpu->regs_page) >> PAGE_SHIFT; + regs_pte = pfn_pte(pfn, __pgprot(__PAGE_KERNEL)); + switcher_pte_page[(unsigned long)pages/PAGE_SIZE%PTRS_PER_PTE] = regs_pte; +} +/*:*/ + +static void free_switcher_pte_pages(void) +{ + unsigned int i; + + for_each_possible_cpu(i) + free_page((long)switcher_pte_page(i)); +} + +/*H:520 Setting up the Switcher PTE page for given CPU is fairly easy, given + * the CPU number and the "struct page"s for the Switcher code itself. + * + * Currently the Switcher is less than a page long, so "pages" is always 1. */ +static __init void populate_switcher_pte_page(unsigned int cpu, + struct page *switcher_page[], + unsigned int pages) +{ + unsigned int i; + pte_t *pte = switcher_pte_page(cpu); + + /* The first entries are easy: they map the Switcher code. */ + for (i = 0; i < pages; i++) { + pte[i] = mk_pte(switcher_page[i], + __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)); + } + + /* The only other thing we map is this CPU's pair of pages. */ + i = pages + cpu*2; + + /* First page (Guest registers) is writable from the Guest */ + pte[i] = pfn_pte(page_to_pfn(switcher_page[i]), + __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED|_PAGE_RW)); + + /* The second page contains the "struct lguest_ro_state", and is + * read-only. */ + pte[i+1] = pfn_pte(page_to_pfn(switcher_page[i+1]), + __pgprot(_PAGE_PRESENT|_PAGE_ACCESSED)); +} + +/* We've made it through the page table code. Perhaps our tired brains are + * still processing the details, or perhaps we're simply glad it's over. + * + * If nothing else, note that all this complexity in juggling shadow page tables + * in sync with the Guest's page tables is for one reason: for most Guests this + * page table dance determines how bad performance will be. This is why Xen + * uses exotic direct Guest pagetable manipulation, and why both Intel and AMD + * have implemented shadow page table support directly into hardware. + * + * There is just one file remaining in the Host. */ + +/*H:510 At boot or module load time, init_pagetables() allocates and populates + * the Switcher PTE page for each CPU. */ +__init int init_pagetables(struct page **switcher_page, unsigned int pages) +{ + unsigned int i; + + for_each_possible_cpu(i) { + switcher_pte_page(i) = (pte_t *)get_zeroed_page(GFP_KERNEL); + if (!switcher_pte_page(i)) { + free_switcher_pte_pages(); + return -ENOMEM; + } + populate_switcher_pte_page(i, switcher_page, pages); + } + return 0; +} +/*:*/ + +/* Cleaning up simply involves freeing the PTE page for each CPU. */ +void free_pagetables(void) +{ + free_switcher_pte_pages(); +} |
