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powerpc: Prevent gcc to re-read the pagetables

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GCC is very likely to read the pagetables just once and cache them in
the local stack or in a register, but it is can also decide to re-read
the pagetables. The problem is that the pagetable in those places can
change from under gcc.

With THP/hugetlbfs the pmd (and pgd for hugetlbfs giga pages) can
change under gup_fast. The pages won't be freed untill we finish
gup fast because we have irq disabled and we free these pages via
rcu callback.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Aneesh Kumar K.V 2013-06-20 14:30:23 +05:30 committed by Benjamin Herrenschmidt
parent 0ac52dd766
commit 7888b4ddb4
2 changed files with 5 additions and 5 deletions
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8
arch/powerpc/mm/gup.c
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@ -34,7 +34,7 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
ptep = pte_offset_kernel(&pmd, addr);
do {
pte_t pte = *ptep;
pte_t pte = ACCESS_ONCE(*ptep);
struct page *page;
if ((pte_val(pte) & mask) != result)
@ -63,7 +63,7 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
pmdp = pmd_offset(&pud, addr);
do {
pmd_t pmd = *pmdp;
pmd_t pmd = ACCESS_ONCE(*pmdp);
next = pmd_addr_end(addr, end);
/*
@ -97,7 +97,7 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
pudp = pud_offset(&pgd, addr);
do {
pud_t pud = *pudp;
pud_t pud = ACCESS_ONCE(*pudp);
next = pud_addr_end(addr, end);
if (pud_none(pud))
@ -160,7 +160,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
pgdp = pgd_offset(mm, addr);
do {
pgd_t pgd = *pgdp;
pgd_t pgd = ACCESS_ONCE(*pgdp);
pr_devel(" %016lx: normal pgd %p\n", addr,
(void *)pgd_val(pgd));

2
arch/powerpc/mm/hugetlbpage.c
View File

@ -1024,7 +1024,7 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr,
if (pte_end < end)
end = pte_end;
pte = *ptep;
pte = ACCESS_ONCE(*ptep);
mask = _PAGE_PRESENT | _PAGE_USER;
if (write)
mask |= _PAGE_RW;