Public bug reported:
[Impact]
With hardware dirty bit management enabled calling pte_wrprotect() on a
dirty PTE will clean the dirty state without flushing the content of the
page to the backing store.
[Test case]
Bug reported by Amazon, a specific test case is not provided. This
problem has been hit by a customer.
[Fix]
Apply commit:
ff1712f953e27f0b0718762ec17d0adb15c9fd0b ("arm64: pgtable: Ensure dirty bit is
preserved across pte_wrprotect()")
Backport activity is minimal, it only requires to adjust the context a
bit to remove the previous pte_wrprotect() implementation.
[Regression potential]
The fix is specific for arm64 pgtable, it is an upstream fix also marked
for stable. The only potential downside could be the extra overhead
introduced by the additional call to pte_mkdirty() in pte_wrprotect(),
so worst case scenario it could introduce a performance regression. It
doesn't seem to potentially introduce any other kind of regression /
breakage.
** Affects: linux-aws (Ubuntu)
Importance: Undecided
Status: New
** Affects: linux-aws (Ubuntu Bionic)
Importance: Undecided
Status: New
** Affects: linux-aws (Ubuntu Focal)
Importance: Undecided
Status: New
** Affects: linux-aws (Ubuntu Groovy)
Importance: Undecided
Status: New
** Affects: linux-aws (Ubuntu Hirsute)
Importance: Undecided
Status: New
** Also affects: linux-aws (Ubuntu Groovy)
Importance: Undecided
Status: New
** Also affects: linux-aws (Ubuntu Hirsute)
Importance: Undecided
Status: New
** Also affects: linux-aws (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: linux-aws (Ubuntu Focal)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1908503
Title:
arm64: prevent losing page dirty state
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