From: Steve Capper <steve.capper@arm.com>
Date: Fri, 1 Dec 2017 17:22:14 +0000
Subject: arm64: mm: Fix pte_mkclean, pte_mkdirty semantics
Git-commit: 8781bcbc5e69d7da69e84c7044ca0284848d5d01
Patch-mainline: v4.15-rc4
References: bsc#1175526
On systems with hardware dirty bit management, the ltp madvise09 unit
test fails due to dirty bit information being lost and pages being
incorrectly freed.
This was bisected to:
arm64: Ignore hardware dirty bit updates in ptep_set_wrprotect()
Reverting this commit leads to a separate problem, that the unit test
retains pages that should have been dropped due to the function
madvise_free_pte_range(.) not cleaning pte's properly.
Currently pte_mkclean only clears the software dirty bit, thus the
following code sequence can appear:
pte = pte_mkclean(pte);
if (pte_dirty(pte))
// this condition can return true with HW DBM!
This patch also adjusts pte_mkclean to set PTE_RDONLY thus effectively
clearing both the SW and HW dirty information.
In order for this to function on systems without HW DBM, we need to
also adjust pte_mkdirty to remove the read only bit from writable pte's
to avoid infinite fault loops.
Cc: <stable@vger.kernel.org>
Fixes: 64c26841b349 ("arm64: Ignore hardware dirty bit updates in ptep_set_wrprotect()")
Reported-by: Bhupinder Thakur <bhupinder.thakur@linaro.org>
Tested-by: Bhupinder Thakur <bhupinder.thakur@linaro.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@suse.com>
---
arch/arm64/include/asm/pgtable.h | 33 +++++++++++++++++---------------
1 file changed, 18 insertions(+), 15 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 149d05fb9421..3ff03a755c32 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -149,12 +149,20 @@ static inline pte_t pte_mkwrite(pte_t pte)
static inline pte_t pte_mkclean(pte_t pte)
{
- return clear_pte_bit(pte, __pgprot(PTE_DIRTY));
+ pte = clear_pte_bit(pte, __pgprot(PTE_DIRTY));
+ pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
+
+ return pte;
}
static inline pte_t pte_mkdirty(pte_t pte)
{
- return set_pte_bit(pte, __pgprot(PTE_DIRTY));
+ pte = set_pte_bit(pte, __pgprot(PTE_DIRTY));
+
+ if (pte_write(pte))
+ pte = clear_pte_bit(pte, __pgprot(PTE_RDONLY));
+
+ return pte;
}
static inline pte_t pte_mkold(pte_t pte)
@@ -641,28 +649,23 @@ static inline pmd_t pmdp_huge_get_and_clear(struct mm_struct *mm,
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
/*
- * ptep_set_wrprotect - mark read-only while preserving the hardware update of
- * the Access Flag.
+ * ptep_set_wrprotect - mark read-only while trasferring potential hardware
+ * dirty status (PTE_DBM && !PTE_RDONLY) to the software PTE_DIRTY bit.
*/
#define __HAVE_ARCH_PTEP_SET_WRPROTECT
static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long address, pte_t *ptep)
{
pte_t old_pte, pte;
- /*
- * ptep_set_wrprotect() is only called on CoW mappings which are
- * private (!VM_SHARED) with the pte either read-only (!PTE_WRITE &&
- * PTE_RDONLY) or writable and software-dirty (PTE_WRITE &&
- * !PTE_RDONLY && PTE_DIRTY); see is_cow_mapping() and
- * protection_map[]. There is no race with the hardware update of the
- * dirty state: clearing of PTE_RDONLY when PTE_WRITE (a.k.a. PTE_DBM)
- * is set.
- */
- VM_WARN_ONCE(pte_write(*ptep) && !pte_dirty(*ptep),
- "%s: potential race with hardware DBM", __func__);
pte = READ_ONCE(*ptep);
do {
old_pte = pte;
+ /*
+ * If hardware-dirty (PTE_WRITE/DBM bit set and PTE_RDONLY
+ * clear), set the PTE_DIRTY bit.
+ */
+ if (pte_hw_dirty(pte))
+ pte = pte_mkdirty(pte);
pte = pte_wrprotect(pte);
pte_val(pte) = cmpxchg_relaxed(&pte_val(*ptep),
pte_val(old_pte), pte_val(pte));
--
2.26.2