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Message-ID: <Zlog5Yk_Pjq0jQhC@linux.dev>
Date: Fri, 31 May 2024 12:11:33 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: James Houghton <jthoughton@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH v4 6/7] KVM: arm64: Relax locking for kvm_test_age_gfn
and kvm_age_gfn
On Wed, May 29, 2024 at 06:05:09PM +0000, James Houghton wrote:
[...]
> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 9e2bbee77491..eabb07c66a07 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c
> @@ -1319,10 +1319,8 @@ static int stage2_age_walker(const struct kvm_pgtable_visit_ctx *ctx,
> data->young = true;
>
> /*
> - * stage2_age_walker() is always called while holding the MMU lock for
> - * write, so this will always succeed. Nonetheless, this deliberately
> - * follows the race detection pattern of the other stage-2 walkers in
> - * case the locking mechanics of the MMU notifiers is ever changed.
> + * This walk may not be exclusive; the PTE is permitted to change
> + * from under us.
> */
> if (data->mkold && !stage2_try_set_pte(ctx, new))
> return -EAGAIN;
It is probably worth mentioning that if there was a race to update the
PTE then the GFN is most likely young, so failing to clear AF probably
isn't even consequential.
--
Thanks,
Oliver
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