Re: [PATCH v1 4/7] mm/ksm: fix KSM COW breaking with userfaultfd-wp via FAULT_FLAG_UNSHARE

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On Fri, 30 Sep 2022 16:19:28 +0200 David Hildenbrand <david@xxxxxxxxxx> wrote:

> Let's stop breaking COW via a fake write fault and let's use
> FAULT_FLAG_UNSHARE instead. This avoids any wrong side effects of the fake
> write fault, such as mapping the PTE writable and marking the pte
> dirty/softdirty.
> 
> Also, this fixes KSM interaction with userfaultfd-wp: when we have a KSM
> page that's write-protected by userfaultfd, break_ksm()->handle_mm_fault()
> will fail with VM_FAULT_SIGBUS and will simpy return in break_ksm() with 0.
> The warning in dmesg indicates this wrong handling:

We're at -rc7.  I'd prefer to avoid merging larger patchsets at this
time.

Is there some minimal fix for 6.0 and -stable?  Or is the problem
non-serious enough to only fix it in 6.1 and later?



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