[PATCH 6.12.y] KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation

[PATCH 6.12.y] KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation

[Hyunwoo Kim]

[ 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() returns void in 6.12.y, so the context
  differs from upstream (return; instead of return ret;). The
  __kvm_find_s1_desc_level() hunk (Fixes: 50f77dc87f13) is dropped, as
  that function is v6.18+ and absent here; only the __kvm_at_s12() /
  kvm_walk_nested_s2() change (Fixes: be04cebf3e78) applies. ]
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
 arch/arm64/kvm/at.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
index 39f0e87a340e..8192bc0bbc87 100644
--- a/arch/arm64/kvm/at.c
+++ b/arch/arm64/kvm/at.c
@@ -1087,7 +1087,8 @@ 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;
 
-- 
2.43.0

Re: [PATCH 6.12.y] KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation

[Marc Zyngier]

On Tue, 09 Jun 2026 11:13:36 +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() returns void in 6.12.y, so the context
>   differs from upstream (return; instead of return ret;). The
>   __kvm_find_s1_desc_level() hunk (Fixes: 50f77dc87f13) is dropped, as
>   that function is v6.18+ and absent here; only the __kvm_at_s12() /
>   kvm_walk_nested_s2() change (Fixes: be04cebf3e78) applies. ]
> Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>

I don't think this is necessary. 6.12 doesn't actually have NV support
(it was enabled only from userspace in 6.17), therefore the ATS12
emulation isn't reachable.

Thanks,

	M.

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

Re: [PATCH 6.12.y] KVM: arm64: Take the SRCU lock for page table walks in fault injection and AT emulation

[Hyunwoo Kim]

On Tue, Jun 09, 2026 at 11:33:09AM +0100, Marc Zyngier wrote:
> On Tue, 09 Jun 2026 11:13:36 +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() returns void in 6.12.y, so the context
> >   differs from upstream (return; instead of return ret;). The
> >   __kvm_find_s1_desc_level() hunk (Fixes: 50f77dc87f13) is dropped, as
> >   that function is v6.18+ and absent here; only the __kvm_at_s12() /
> >   kvm_walk_nested_s2() change (Fixes: be04cebf3e78) applies. ]
> > Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
> 
> I don't think this is necessary. 6.12 doesn't actually have NV support
> (it was enabled only from userspace in 6.17), therefore the ATS12
> emulation isn't reachable.

Ah, I see. Thank you for the review.

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


Best regards,
Hyunwoo Kim