Re: [PATCH 0/2] KVM: arm64: Fix for mapping incorrect PA at stage-2

[Marc Zyngier <maz@kernel.org>]

On Fri, 21 Apr 2023 08:16:04 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> Ugh.
> 
> So it appears that there is a race between two parallel stage-2 map
> walkers that could lead to mapping the incorrect PA for a given IPA, as
> the IPA -> PA relationship picks up an unintended offset. This series
> eliminates the problem by using the current IPA of the walk as the
> source-of-truth regarding where we are in a map operation. If you're
> curious about the race, it is spelled out in the first patch.

Ugh indeed.

> 
> While there is no such race to update hyp's stage-1, the second patch
> applies the same rationale to hyp stage-1 walks for the sake of
> consistency.
> 
> Applies to 6.3-rc3, and merges w/o conflict into kvmarm/next. Took this
> for a ride with selftests, kvm-unit-tests, QEMU, and our internal VMM
> (affectionately referred to as Vanadium on the list from time to time).
> I also ran through the gamut of nVHE, VHE, and pKVM given the effects on
> hyp stage-1.
> 
> Marc, the bug can have some rather ugly (albeit rare) consequences, so
> I'd like to get this in ASAP. The door is shut on 6.3, but it'd be nice
> to squeeze in the 6.4 pull request if possible.

This is a pretty invasive change, and I'd really like to give it some
-next exposure. I'm not doubting your testing, but experience shows
that there is always someone with a more tricky setup...

What I'd suggest is to not include it in the pull request that I'm
about to send today, but to let it simmer in -next for a week. This
will give us some confidence that we're OK, and also avoid being
shouted at for sending stuff that hasn't been in -next at all.

If everything checks out after a week, I'll send another PR with this
fix (and whatever will have landed in the meantime).

Would that work for you?

	M.

-- 
Without deviation from the norm, progress is not possible.