Re: [PATCH 4/4] KVM: arm64: Check HCR_EL2 instead of shadow copy to swap PtrAuth registers

Mark Rutland
2020-06-15T10:25:57Z

On Mon, Jun 15, 2020 at 09:19:54AM +0100, Marc Zyngier wrote:
> When save/restoring PtrAuth registers between host and guest, it is
> pretty useless to fetch the in-memory state, while we have the right
> state in the HCR_EL2 system register. Use that instead.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>

It took me a while to spot that we switched the guest/host hcr_el2 value
in the __activate_traps() and __deactivate_traps() paths, but given that
this is only called in the __kvm_vcpu_run_*() paths called between
those, I agree this is sound. Given that:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> arch/arm64/include/asm/kvm_ptrauth.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_ptrauth.h b/arch/arm64/include/asm/kvm_ptrauth.h
> index 6301813dcace..f1830173fa9e 100644
> --- a/arch/arm64/include/asm/kvm_ptrauth.h
> +++ b/arch/arm64/include/asm/kvm_ptrauth.h
> @@ -74,7 +74,7 @@ alternative_if_not ARM64_HAS_ADDRESS_AUTH_IMP_DEF
> b 1001f
> alternative_else_nop_endif
> 1000:
> - ldr \reg1, [\g_ctxt, #(VCPU_HCR_EL2 - VCPU_CONTEXT)]
> + mrs \reg1, hcr_el2
> and \reg1, \reg1, #(HCR_API | HCR_APK)
> cbz \reg1, 1001f
> add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1
> @@ -90,7 +90,7 @@ alternative_if_not ARM64_HAS_ADDRESS_AUTH_IMP_DEF
> b 2001f
> alternative_else_nop_endif
> 2000:
> - ldr \reg1, [\g_ctxt, #(VCPU_HCR_EL2 - VCPU_CONTEXT)]
> + mrs \reg1, hcr_el2
> and \reg1, \reg1, #(HCR_API | HCR_APK)
> cbz \reg1, 2001f
> add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1
> --
> 2.27.0
>
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