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SubjectRe: [PATCH 3/3] mm/uffd: Detect pgtable allocation failures
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On 04.01.23 23:52, Peter Xu wrote:
> Before this patch, when there's any pgtable allocation issues happened
> during change_protection(), the error will be ignored from the syscall.
> For shmem, there will be an error dumped into the host dmesg. Two issues
> with that:
>
> (1) Doing a trace dump when allocation fails is not anything close to
> grace..

s/..//

>
> (2) The user should be notified with any kind of such error, so the user
> can trap it and decide what to do next, either by retrying, or stop
> the process properly, or anything else.
>
> For userfault users, this will change the API of UFFDIO_WRITEPROTECT when
> pgtable allocation failure happened. It should not normally break anyone,
> though. If it breaks, then in good ways.
>
> One man-page update will be on the way to introduce the new -ENOMEM for
> UFFDIO_WRITEPROTECT. Not marking stable so we keep the old behavior on the
> 5.19-till-now kernels.

We'd now fail after already having modified some state (protected some
PTEs). I assume that can already happen when protecting across multiple
VMAs and is expected, right?

--
Thanks,

David / dhildenb

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