On Fri, 02 Apr 2010, NIIBE Yutaka wrote:
> NIIBE Yutaka wrote:
>> To have same semantics as other archs, I think that VIPT-WB cache
>> machine should have cache flush at ptep_set_wrprotect, so that memory
>> of the page has up-to-date data. Yes, it will be huge performance
>> impact for fork. But I don't find any good solution other than this
>> yet.
>
> I think we could do something like (only for VIPT-WB cache machine):
>
> - static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long
> address, pte_t *ptep)
>
> + static inline void ptep_set_wrprotect(struct vm_area_struct *vma, struct
> mm_struct *mm, unsigned long addr, pte_t *ptep)
> {
> pte_t old_pte = *ptep;
> + if (atomic_read(&mm->mm_users) > 1)
> + flush_cache_page(vma, addr, pte_pfn(old_pte));
> set_pte_at(mm, addr, ptep, pte_wrprotect(old_pte));
> }
I tested the hack below on two machines currently running 2.6.33.2
UP kernels. The change seems to fix Debian #561203 (minifail bug)!
Thus, I definitely think you are on the right track. I'll continue
to test.
I suspect the same issue is present for SMP kernels.
Thanks,
Dave
--
J. David Anglin dave.anglin@xxxxxxxxxxxxxx
National Research Council of Canada (613) 990-0752 (FAX: 952-6602)
diff --git a/arch/parisc/include/asm/pgtable.h b/arch/parisc/include/asm/pgtable.h
index a27d2e2..a5d730f 100644
--- a/arch/parisc/include/asm/pgtable.h
+++ b/arch/parisc/include/asm/pgtable.h
@@ -14,6 +14,7 @@
#include <linux/bitops.h>
#include <asm/processor.h>
#include <asm/cache.h>
+extern void flush_cache_page(struct vm_area_struct *vma, unsigned long vmaddr, unsigned long pfn);
/*
* kern_addr_valid(ADDR) tests if ADDR is pointing to valid kernel
@@ -456,7 +457,7 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm, unsigned long addr,
return old_pte;
}
-static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
+static inline void ptep_set_wrprotect(struct vm_area_struct *vma, struct mm_struct *mm, unsigned long addr, pte_t *ptep)
{
#ifdef CONFIG_SMP
unsigned long new, old;
@@ -467,6 +468,8 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
} while (cmpxchg((unsigned long *) ptep, old, new) != old);
#else
pte_t old_pte = *ptep;
+ if (atomic_read(&mm->mm_users) > 1)
+ flush_cache_page(vma, addr, pte_pfn(old_pte));
set_pte_at(mm, addr, ptep, pte_wrprotect(old_pte));
#endif
}
diff --git a/mm/memory.c b/mm/memory.c
index 09e4b1b..21c2916 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -616,7 +616,7 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
* in the parent and the child
*/
if (is_cow_mapping(vm_flags)) {
- ptep_set_wrprotect(src_mm, addr, src_pte);
+ ptep_set_wrprotect(vma, src_mm, addr, src_pte);
pte = pte_wrprotect(pte);
}
--
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