[PATCH] arm64: kvm: Prevent restoring stale PMSCR_EL1 for vcpu

[PATCH] arm64: kvm: Prevent restoring stale PMSCR_EL1 for vcpu

[Julien Thierry]

When VHE is not present, KVM needs to save and restores PMSCR_EL1 when
possible. If SPE is used by the host, value of PMSCR_EL1 cannot be saved
for the guest.
If the host starts using SPE between two save+restore on the same vcpu,
restore will write the value of PMSCR_EL1 read during the first save.

Make sure __debug_save_spe_nvhe clears the value of the saved PMSCR_EL1
when the guest cannot use SPE.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: <stable@vger.kernel.org>
---
 arch/arm64/kvm/hyp/debug-sr.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
index 321c9c0..f4363d4 100644
--- a/arch/arm64/kvm/hyp/debug-sr.c
+++ b/arch/arm64/kvm/hyp/debug-sr.c
@@ -74,6 +74,9 @@ static void __hyp_text __debug_save_spe_nvhe(u64 *pmscr_el1)
 {
 	u64 reg;

+	/* Clear pmscr in case of early return */
+	*pmscr_el1 = 0;
+
 	/* SPE present on this CPU? */
 	if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1),
 						  ID_AA64DFR0_PMSVER_SHIFT))
--
1.9.1

[PATCH] arm64: kvm: Prevent restoring stale PMSCR_EL1 for vcpu

[Will Deacon]

On Wed, Dec 06, 2017 at 05:09:49PM +0000, Julien Thierry wrote:
> When VHE is not present, KVM needs to save and restores PMSCR_EL1 when
> possible. If SPE is used by the host, value of PMSCR_EL1 cannot be saved
> for the guest.
> If the host starts using SPE between two save+restore on the same vcpu,
> restore will write the value of PMSCR_EL1 read during the first save.
> 
> Make sure __debug_save_spe_nvhe clears the value of the saved PMSCR_EL1
> when the guest cannot use SPE.

Ok, so the problem is that we have a stale (non-zero) saved pmscr_el1,
and therefore the restore code unconditionally restores that even though
SPE is no longer in use by the host. Well spotted!

> Signed-off-by: Julien Thierry <julien.thierry@arm.com>
> Cc: Christoffer Dall <christoffer.dall@linaro.org>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: <stable@vger.kernel.org>
> ---
>  arch/arm64/kvm/hyp/debug-sr.c | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Will Deacon <will.deacon@arm.com>

Will

[PATCH] arm64: kvm: Prevent restoring stale PMSCR_EL1 for vcpu

[Christoffer Dall]

On Wed, Dec 06, 2017 at 05:09:49PM +0000, Julien Thierry wrote:
> When VHE is not present, KVM needs to save and restores PMSCR_EL1 when
> possible. If SPE is used by the host, value of PMSCR_EL1 cannot be saved
> for the guest.
> If the host starts using SPE between two save+restore on the same vcpu,
> restore will write the value of PMSCR_EL1 read during the first save.
> 
> Make sure __debug_save_spe_nvhe clears the value of the saved PMSCR_EL1
> when the guest cannot use SPE.
> 
> Signed-off-by: Julien Thierry <julien.thierry@arm.com>
> Cc: Christoffer Dall <christoffer.dall@linaro.org>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: <stable@vger.kernel.org>
> ---
>  arch/arm64/kvm/hyp/debug-sr.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
> index 321c9c0..f4363d4 100644
> --- a/arch/arm64/kvm/hyp/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/debug-sr.c
> @@ -74,6 +74,9 @@ static void __hyp_text __debug_save_spe_nvhe(u64 *pmscr_el1)
>  {
>  	u64 reg;
> 
> +	/* Clear pmscr in case of early return */
> +	*pmscr_el1 = 0;
> +
>  	/* SPE present on this CPU? */
>  	if (!cpuid_feature_extract_unsigned_field(read_sysreg(id_aa64dfr0_el1),
>  						  ID_AA64DFR0_PMSVER_SHIFT))
> --
> 1.9.1

Applied, thanks.
-Christoffer