[RFC PATCH v2 28/41] arm64: KVM: Treat SVE use by guests as undefined instruction execution

[mark.rutland@arm.com (Mark Rutland)]

Hi,

On Wed, Mar 22, 2017 at 02:50:58PM +0000, Dave Martin wrote:
> We don't currently support context-switching of Scalable Vector
> Extension context between vcpus, and the SVE access exception is
> thus left masked by default at EL2 when running a vcpu.
> 
> However, there's nothing to stop a guest trying to use SVE.  If it
> does, we'll get an SVE access exception to EL2 which will cause KVM
> to panic since this exception isn't yet recognised.
> 
> This patch adds knowledge to KVM about the SVE access exception,
> translating it into an undefined instruction exception injected to
> the vcpu.
> 
> This prevents a malicious guest from panicking the host by
> attempted SVE use.
> 
> SVE-enabled guests will still not work properly for now, but they
> won't take the host down.
> 
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> ---
>  arch/arm64/kvm/handle_exit.c | 8 ++++++++
>  1 file changed, 8 insertions(+)

As a heads-up, this is handled implicitly by kvm_handle_unknown_ec()
since commit ba4dd156eabdca93 ("arm64: KVM: Survive unknown traps from
guests"). That also logs a (ratelimited) warning regarding the
unimplemented trap handling.

Given that, I think we can drop this patch until actual support lands.

Thanks,
Mark.

> 
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index fa1b18e..e43b147 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -146,6 +146,13 @@ static int kvm_handle_unknown_ec(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  	return 1;
>  }
>  
> +static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run)
> +{
> +	/* Until SVE is supported for guests: */
> +	kvm_inject_undefined(vcpu);
> +	return 1;
> +}
> +
>  static exit_handle_fn arm_exit_handlers[] = {
>  	[0 ... ESR_ELx_EC_MAX]	= kvm_handle_unknown_ec,
>  	[ESR_ELx_EC_WFx]	= kvm_handle_wfx,
> @@ -159,6 +166,7 @@ static exit_handle_fn arm_exit_handlers[] = {
>  	[ESR_ELx_EC_HVC64]	= handle_hvc,
>  	[ESR_ELx_EC_SMC64]	= handle_smc,
>  	[ESR_ELx_EC_SYS64]	= kvm_handle_sys_reg,
> +	[ESR_ELx_EC_SVE]	= handle_sve,
>  	[ESR_ELx_EC_IABT_LOW]	= kvm_handle_guest_abort,
>  	[ESR_ELx_EC_DABT_LOW]	= kvm_handle_guest_abort,
>  	[ESR_ELx_EC_SOFTSTP_LOW]= kvm_handle_guest_debug,
> -- 
> 2.1.4
> 
> 
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