Re: [PATCH 6.18.y] KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation

[Marc Zyngier <maz@kernel.org>]

On Tue, 09 Jun 2026 10:48:08 +0100,
Hyunwoo Kim <imv4bel@gmail.com> wrote:
> 
> [ Upstream commit f2ca45b50d4216c9cc7ffabf50d9ad1932209251 ]
> 
> walk_s1() and kvm_walk_nested_s2() expect to be called while holding
> kvm->srcu to guard against memslot changes. While this is generally
> the case, __kvm_at_s12() and __kvm_find_s1_desc_level() call into the
> respective walkers without taking kvm->srcu.
> 
> Fix by acquiring kvm->srcu prior to the table walk in both instances.
> 
> Cc: stable@vger.kernel.org
> Fixes: 50f77dc87f13 ("KVM: arm64: Populate level on S1PTW SEA injection")
> Fixes: be04cebf3e78 ("KVM: arm64: nv: Add emulation of AT S12E{0,1}{R,W}")
> Suggested-by: Oliver Upton <oupton@kernel.org>
> Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
> Reviewed-by: Oliver Upton <oupton@kernel.org>
> Link: https://patch.msgid.link/aiAZfdeyanIvP8SD@v4bel
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> [ Hyunwoo Kim: __kvm_at_s12() still returns void in 6.18.y, so the
>   surrounding context differs from upstream (return; instead of
>   return ret;); the added scoped_guard() is unchanged. ]
> Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
> ---
>  arch/arm64/kvm/at.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
> index be26d5aa668c..e6de6aac6ede 100644
> --- a/arch/arm64/kvm/at.c
> +++ b/arch/arm64/kvm/at.c
> @@ -1528,7 +1528,8 @@ void __kvm_at_s12(struct kvm_vcpu *vcpu, u32 op, u64 vaddr)
>  	/* Do the stage-2 translation */
>  	ipa = (par & GENMASK_ULL(47, 12)) | (vaddr & GENMASK_ULL(11, 0));
>  	out.esr = 0;
> -	ret = kvm_walk_nested_s2(vcpu, ipa, &out);
> +	scoped_guard(srcu, &vcpu->kvm->srcu)
> +		ret = kvm_walk_nested_s2(vcpu, ipa, &out);
>  	if (ret < 0)
>  		return;
>  
> @@ -1623,7 +1624,8 @@ int __kvm_find_s1_desc_level(struct kvm_vcpu *vcpu, u64 va, u64 ipa, int *level)
>  	}
>  
>  	/* Walk the guest's PT, looking for a match along the way */
> -	ret = walk_s1(vcpu, &wi, &wr, va);
> +	scoped_guard(srcu, &vcpu->kvm->srcu)
> +		ret = walk_s1(vcpu, &wi, &wr, va);
>  	switch (ret) {
>  	case -EINTR:
>  		/* We interrupted the walk on a match, return the level */

Thanks for going the extra mile and doing the backport, much
appreciated.

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

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