[PATCH] KVM: arm64: Skip instruction after emulating write to TCR_EL1

[PATCH] KVM: arm64: Skip instruction after emulating write to TCR_EL1

[Oliver Upton]

Whelp, this is embarrassing. Since commit 082fdfd13841 ("KVM: arm64:
Prevent guests from enabling HA/HD on Ampere1") KVM traps writes to
TCR_EL1 on AmpereOne to work around an erratum in the unadvertised
HAFDBS implementation, preventing the guest from enabling the feature.
Unfortunately, I failed virtualization 101 when working on that change,
and forgot to advance PC after instruction emulation.

Do the right thing and skip the MSR instruction after emulating the
write.

Fixes: 082fdfd13841 ("KVM: arm64: Prevent guests from enabling HA/HD on Ampere1")
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/hyp/include/hyp/switch.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index 4bddb8541bec..34f222af6165 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -457,6 +457,7 @@ static bool handle_ampere1_tcr(struct kvm_vcpu *vcpu)
 	 */
 	val &= ~(TCR_HD | TCR_HA);
 	write_sysreg_el1(val, SYS_TCR);
+	__kvm_skip_instr(vcpu);
 	return true;
 }
 

base-commit: 01b94b0f3922039f7d3e0d1eeb33b8891746b65f
-- 
2.41.0.487.g6d72f3e995-goog

Re: [PATCH] KVM: arm64: Skip instruction after emulating write to TCR_EL1

[Marc Zyngier]

On Fri, 28 Jul 2023 01:08:24 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> Whelp, this is embarrassing. Since commit 082fdfd13841 ("KVM: arm64:
> Prevent guests from enabling HA/HD on Ampere1") KVM traps writes to
> TCR_EL1 on AmpereOne to work around an erratum in the unadvertised
> HAFDBS implementation, preventing the guest from enabling the feature.
> Unfortunately, I failed virtualization 101 when working on that change,
> and forgot to advance PC after instruction emulation.
> 
> Do the right thing and skip the MSR instruction after emulating the
> write.
> 
> Fixes: 082fdfd13841 ("KVM: arm64: Prevent guests from enabling HA/HD on Ampere1")
> Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

Oh hum... I think it is high time for a new PR to Paolo!

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

	M.

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

Re: [PATCH] KVM: arm64: Skip instruction after emulating write to TCR_EL1

[Oliver Upton]

On Fri, Jul 28, 2023 at 09:14:14AM +0100, Marc Zyngier wrote:
> On Fri, 28 Jul 2023 01:08:24 +0100,
> Oliver Upton <oliver.upton@linux.dev> wrote:
> > 
> > Whelp, this is embarrassing. Since commit 082fdfd13841 ("KVM: arm64:
> > Prevent guests from enabling HA/HD on Ampere1") KVM traps writes to
> > TCR_EL1 on AmpereOne to work around an erratum in the unadvertised
> > HAFDBS implementation, preventing the guest from enabling the feature.
> > Unfortunately, I failed virtualization 101 when working on that change,
> > and forgot to advance PC after instruction emulation.
> > 
> > Do the right thing and skip the MSR instruction after emulating the
> > write.
> > 
> > Fixes: 082fdfd13841 ("KVM: arm64: Prevent guests from enabling HA/HD on Ampere1")
> > Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> 
> Oh hum... I think it is high time for a new PR to Paolo!

Definitely, now let's sweep this mess under the rug :)

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

Appreciated!

-- 
Thanks,
Oliver

Re: [PATCH] KVM: arm64: Skip instruction after emulating write to TCR_EL1

[Oliver Upton]

On Fri, 28 Jul 2023 00:08:24 +0000, Oliver Upton wrote:
> Whelp, this is embarrassing. Since commit 082fdfd13841 ("KVM: arm64:
> Prevent guests from enabling HA/HD on Ampere1") KVM traps writes to
> TCR_EL1 on AmpereOne to work around an erratum in the unadvertised
> HAFDBS implementation, preventing the guest from enabling the feature.
> Unfortunately, I failed virtualization 101 when working on that change,
> and forgot to advance PC after instruction emulation.
> 
> [...]

Applied to kvmarm/fixes, thanks!

[1/1] KVM: arm64: Skip instruction after emulating write to TCR_EL1
      https://git.kernel.org/kvmarm/kvmarm/c/74158a8cad79

--
Best,
Oliver