x86: Flush TLB if PGD entry is changed in i386 PAE mode

According to intel CPU manual, every time PGD entry is changed in i386 PAE mode, we need do a full TLB flush. Current code follows this and there is comment for this too in the code. But current code misses the multi-threaded case. A changed page table might be used by several CPUs, every such CPU should flush TLB. Usually this isn't a problem, because we prepopulate all PGD entries at process fork. But when the process does munmap and follows new mmap, this issue will be triggered. When it happens, some CPUs keep doing page faults: http://marc.info/?l=linux-kernel&m=129915020508238&w=2 Reported-by: Yasunori Goto<[email protected]> Tested-by: Yasunori Goto<[email protected]> Reviewed-by: Rik van Riel <[email protected]> Signed-off-by: Shaohua Li<[email protected]> Cc: Mallick Asit K <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Andrew Morton <[email protected]> Cc: linux-mm <[email protected]> Cc: stable <[email protected]> LKML-Reference: <1300246649.2337.95.camel@sli10-conroe> Signed-off-by: Ingo Molnar <[email protected]>
gunnarahlberg · Mar 18, 2011 · 4981d01 · 4981d01
1 parent e8e999c
commit 4981d01
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diff --git a/arch/x86/include/asm/pgtable-3level.h b/arch/x86/include/asm/pgtable-3level.h
@@ -69,8 +69,6 @@ static inline void native_pmd_clear(pmd_t *pmd)
 
 static inline void pud_clear(pud_t *pudp)
 {
-	unsigned long pgd;
-
 	set_pud(pudp, __pud(0));
 
 	/*
@@ -79,13 +77,10 @@ static inline void pud_clear(pud_t *pudp)
 	 * section 8.1: in PAE mode we explicitly have to flush the
 	 * TLB via cr3 if the top-level pgd is changed...
 	 *
-	 * Make sure the pud entry we're updating is within the
-	 * current pgd to avoid unnecessary TLB flushes.
+	 * Currently all places where pud_clear() is called either have
+	 * flush_tlb_mm() followed or don't need TLB flush (x86_64 code or
+	 * pud_clear_bad()), so we don't need TLB flush here.
 	 */
-	pgd = read_cr3();
-	if (__pa(pudp) >= pgd && __pa(pudp) <
-	    (pgd + sizeof(pgd_t)*PTRS_PER_PGD))
-		write_cr3(pgd);
 }
 
 #ifdef CONFIG_SMP

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
@@ -168,8 +168,7 @@ void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd)
 	 * section 8.1: in PAE mode we explicitly have to flush the
 	 * TLB via cr3 if the top-level pgd is changed...
 	 */
-	if (mm == current->active_mm)
-		write_cr3(read_cr3());
+	flush_tlb_mm(mm);
 }
 #else  /* !CONFIG_X86_PAE */