[PATCH] x86: __pa and __pa_symbol address space separation

Currently __pa_symbol is for use with symbols in the kernel address
map and __pa is for use with pointers into the physical memory map.
But the code is implemented so you can usually interchange the two.

__pa which is much more common can be implemented much more cheaply
if it is it doesn't have to worry about any other kernel address
spaces.  This is especially true with a relocatable kernel as
__pa_symbol needs to peform an extra variable read to resolve
the address.

There is a third macro that is added for the vsyscall data
__pa_vsymbol for finding the physical addesses of vsyscall pages.

Most of this patch is simply sorting through the references to
__pa or __pa_symbol and using the proper one.  A little of
it is continuing to use a physical address when we have it
instead of recalculating it several times.

swapper_pgd is now NULL.  leave_mm now uses init_mm.pgd
and init_mm.pgd is initialized at boot (instead of compile time)
to the physmem virtual mapping of init_level4_pgd.  The
physical address changed.

Except for the for EMPTY_ZERO page all of the remaining references
to __pa_symbol appear to be during kernel initialization.  So this
should reduce the cost of __pa in the common case, even on a relocated
kernel.

As this is technically a semantic change we need to be on the lookout
for anything I missed.  But it works for me (tm).

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>

2 files changed, 4 insertions, 6 deletions

diff --git a/include/asm-x86_64/page.h b/include/asm-x86_64/page.h
index d554b94..4974433 100644
--- a/include/asm-x86_64/page.h
+++ b/include/asm-x86_64/page.h
@@ -102,17 +102,15 @@ typedef struct { unsigned long pgprot; } pgprot_t;
 
 /* Note: __pa(&symbol_visible_to_c) should be always replaced with __pa_symbol.
    Otherwise you risk miscompilation. */ 
-#define __pa(x)			(((unsigned long)(x)>=__START_KERNEL_map)?(unsigned long)(x) - (unsigned long)__START_KERNEL_map:(unsigned long)(x) - PAGE_OFFSET)
+#define __pa(x)			((unsigned long)(x) - PAGE_OFFSET)
 /* __pa_symbol should be used for C visible symbols.
    This seems to be the official gcc blessed way to do such arithmetic. */ 
 #define __pa_symbol(x)		\
 	({unsigned long v;  \
 	  asm("" : "=r" (v) : "0" (x)); \
-	  __pa(v); })
+	  (v - __START_KERNEL_map); })
 
 #define __va(x)			((void *)((unsigned long)(x)+PAGE_OFFSET))
-#define __boot_va(x)		__va(x)
-#define __boot_pa(x)		__pa(x)
 #ifdef CONFIG_FLATMEM
 #define pfn_valid(pfn)		((pfn) < end_pfn)
 #endif
diff --git a/include/asm-x86_64/pgtable.h b/include/asm-x86_64/pgtable.h
index 703f024..c1865e3 100644
--- a/include/asm-x86_64/pgtable.h
+++ b/include/asm-x86_64/pgtable.h
@@ -19,7 +19,7 @@ extern pmd_t level2_kernel_pgt[512];
 extern pgd_t init_level4_pgt[];
 extern unsigned long __supported_pte_mask;
 
-#define swapper_pg_dir init_level4_pgt
+#define swapper_pg_dir ((pgd_t *)NULL)
 
 extern void paging_init(void);
 extern void clear_kernel_mapping(unsigned long addr, unsigned long size);
@@ -29,7 +29,7 @@ extern void clear_kernel_mapping(unsigned long addr, unsigned long size);
  * for zero-mapped memory areas etc..
  */
 extern unsigned long empty_zero_page[PAGE_SIZE/sizeof(unsigned long)];
-#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
+#define ZERO_PAGE(vaddr) (pfn_to_page(__pa_symbol(&empty_zero_page) >> PAGE_SHIFT))
 
 #endif /* !__ASSEMBLY__ */