Re: [PATCH] KVM: arm64: Filter out HCR_EL2.VSE when running in hypervisor context

[Marc Zyngier <maz@kernel.org>]

On 2025-07-20 12:33, Marc Zyngier wrote:
> HCR_EL2.VSE is delivering a virtual SError to the guest, and does not
> affect EL2 itself. However, when computing the host's HCR_EL2 value,
> we take the guest's view of HCR_EL2.VSE at face value, and apply it
> irrespective of the guest's exception level we are returning to.
> 
> The result is that a L1 hypervisor injecting a virtual SError to an L2
> by setting its HCR_EL2.VSE to 1 results in itself getting the SError
> as if it was a physical one if it traps for any reason before returning
> to L2.
> 
> Fix it by filtering HCR_EL2.VSE out when entering the L1 host context.
> 
> Fixes: 04ab519bb86df ("KVM: arm64: nv: Configure HCR_EL2 for FEAT_NV2")
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Cc: stable@vger.kernel.org
> ---
>  arch/arm64/kvm/hyp/vhe/switch.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/kvm/hyp/vhe/switch.c 
> b/arch/arm64/kvm/hyp/vhe/switch.c
> index 477f1580ffeaa..eddda649d9ee1 100644
> --- a/arch/arm64/kvm/hyp/vhe/switch.c
> +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> @@ -68,6 +68,9 @@ static u64 __compute_hcr(struct kvm_vcpu *vcpu)
>  		if (!vcpu_el2_e2h_is_set(vcpu))
>  			hcr |= HCR_NV1;
> 
> +		/* Virtual SErrors only apply to L2, not L1 */
> +		guest_hcr &= ~HCR_VSE;
> +
>  		write_sysreg_s(vcpu->arch.ctxt.vncr_array, SYS_VNCR_EL2);
>  	} else {
>  		host_data_clear_flag(VCPU_IN_HYP_CONTEXT);

Actually, a better fix would be just nuke any bit that doesn't affect
the HYP context. And that's almost all of them, bar the RES1 bits.

I'll repost something once I am done dealing with the rest of the RAS
enabling stuff.

         M.
-- 
Jazz is not dead. It just smells funny...