From 3d28ebceaffab40f30afa87e33331560148d7b8b Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Sun, 28 May 2017 10:00:15 -0700 Subject: x86/mm: Rework lazy TLB to track the actual loaded mm Lazy TLB state is currently managed in a rather baroque manner. AFAICT, there are three possible states: - Non-lazy. This means that we're running a user thread or a kernel thread that has called use_mm(). current->mm == current->active_mm == cpu_tlbstate.active_mm and cpu_tlbstate.state == TLBSTATE_OK. - Lazy with user mm. We're running a kernel thread without an mm and we're borrowing an mm_struct. We have current->mm == NULL, current->active_mm == cpu_tlbstate.active_mm, cpu_tlbstate.state != TLBSTATE_OK (i.e. TLBSTATE_LAZY or 0). The current cpu is set in mm_cpumask(current->active_mm). CR3 points to current->active_mm->pgd. The TLB is up to date. - Lazy with init_mm. This happens when we call leave_mm(). We have current->mm == NULL, current->active_mm == cpu_tlbstate.active_mm, but that mm is only relelvant insofar as the scheduler is tracking it for refcounting. cpu_tlbstate.state != TLBSTATE_OK. The current cpu is clear in mm_cpumask(current->active_mm). CR3 points to swapper_pg_dir, i.e. init_mm->pgd. This patch simplifies the situation. Other than perf, x86 stops caring about current->active_mm at all. We have cpu_tlbstate.loaded_mm pointing to the mm that CR3 references. The TLB is always up to date for that mm. leave_mm() just switches us to init_mm. There are no longer any special cases for mm_cpumask, and switch_mm() switches mms without worrying about laziness. After this patch, cpu_tlbstate.state serves only to tell the TLB flush code whether it may switch to init_mm instead of doing a normal flush. This makes fairly extensive changes to xen_exit_mmap(), which used to look a bit like black magic. Perf is unchanged. With or without this change, perf may behave a bit erratically if it tries to read user memory in kernel thread context. We should build on this patch to teach perf to never look at user memory when cpu_tlbstate.loaded_mm != current->mm. Signed-off-by: Andy Lutomirski Cc: Andrew Morton Cc: Arjan van de Ven Cc: Borislav Petkov Cc: Dave Hansen Cc: Linus Torvalds Cc: Mel Gorman Cc: Michal Hocko Cc: Nadav Amit Cc: Nadav Amit Cc: Peter Zijlstra Cc: Rik van Riel Cc: Thomas Gleixner Cc: linux-mm@kvack.org Signed-off-by: Ingo Molnar --- arch/x86/events/core.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'arch/x86/events') diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 580b60f..77a3309 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2101,8 +2101,7 @@ static int x86_pmu_event_init(struct perf_event *event) static void refresh_pce(void *ignored) { - if (current->active_mm) - load_mm_cr4(current->active_mm); + load_mm_cr4(this_cpu_read(cpu_tlbstate.loaded_mm)); } static void x86_pmu_event_mapped(struct perf_event *event) -- cgit v1.1 From bbf79d21bd4627a01ca8721c9373752819f8e4cc Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Tue, 6 Jun 2017 19:31:16 +0200 Subject: x86/ldt: Rename ldt_struct::size to ::nr_entries ... because this is exactly what it is: the number of entries in the LDT. Calling it "size" is simply confusing and it is actually begging to be called "nr_entries" or somesuch, especially if you see constructs like: alloc_size = size * LDT_ENTRY_SIZE; since LDT_ENTRY_SIZE is the size of a single entry. There should be no functionality change resulting from this patch, as the before/after output from tools/testing/selftests/x86/ldt_gdt.c shows. Signed-off-by: Borislav Petkov Acked-by: Andy Lutomirski Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170606173116.13977-1-bp@alien8.de [ Renamed 'n_entries' to 'nr_entries' ] Signed-off-by: Ingo Molnar --- arch/x86/events/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/events') diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 77a3309..d4d5e1e 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2333,7 +2333,7 @@ static unsigned long get_segment_base(unsigned int segment) /* IRQs are off, so this synchronizes with smp_store_release */ ldt = lockless_dereference(current->active_mm->context.ldt); - if (!ldt || idx > ldt->size) + if (!ldt || idx > ldt->nr_entries) return 0; desc = &ldt->entries[idx]; -- cgit v1.1