Re: [PATCH v6 04/64] KVM: arm64: nv: Allow userspace to set PSR_MODE_EL2x

Alexandru Elisei
2022-02-02T11:53:34Z

Hi Marc,

On Fri, Jan 28, 2022 at 12:18:12PM +0000, Marc Zyngier wrote:
> From: Christoffer Dall <christoffer.dall@linaro.org>
>
> We were not allowing userspace to set a more privileged mode for the VCPU
> than EL1, but we should allow this when nested virtualization is enabled
> for the VCPU.
>
> Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/guest.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index e116c7767730..db6209622be9 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -24,6 +24,7 @@
> #include <asm/fpsimd.h>
> #include <asm/kvm.h>
> #include <asm/kvm_emulate.h>
> +#include <asm/kvm_nested.h>
> #include <asm/sigcontext.h>
>
> #include "trace.h"
> @@ -259,6 +260,11 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
> if (vcpu_el1_is_32bit(vcpu))
> return -EINVAL;
> break;
> + case PSR_MODE_EL2h:
> + case PSR_MODE_EL2t:
> + if (vcpu_el1_is_32bit(vcpu) || !vcpu_has_nv(vcpu))

I'm a bit confused about the vcpu_el1_is_32bit() check. The function tests
that HCR_EL2.RW is not set. HCR_EL2.RW is cleared when the
KVM_ARM_VCPU_EL1_32BIT feature is preset for the VCPU. But the EL2 and the
32BIT features are incompatible (kvm_reset_vcpu() returns an error when
both are set). Wouldn't checking only !vcpu_has_nv() be enough here?

Thanks,
Alex

> + return -EINVAL;
> + break;
> default:
> err = -EINVAL;
> goto out;
> --
> 2.30.2
>