Re: [RFC PATCH v6 3/6] KVM: x86: Reject disabling of MWAIT interception when not allowed

Zhao Liu
2023-01-31T12:04:33Z

On Sat, Jan 21, 2023 at 02:07:35AM +0000, Kechen Lu wrote:
> Date: Sat, 21 Jan 2023 02:07:35 +0000
> From: Kechen Lu <kechenl@nvidia.com>
> Subject: [RFC PATCH v6 3/6] KVM: x86: Reject disabling of MWAIT
> interception when not allowed
> X-Mailer: git-send-email 2.34.1
>
> From: Sean Christopherson <seanjc@google.com>
>
> Reject KVM_CAP_X86_DISABLE_EXITS if userspace attempts to disable MWAIT
> exits and KVM previously reported (via KVM_CHECK_EXTENSION) that MWAIT is
> not allowed in guest, e.g. because it's not supported or the CPU doesn't
> have an aways-running

nit: always-running?

> APIC timer.
>
> Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT intercepts")
>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Kechen Lu <kechenl@nvidia.com>
> ---
> arch/x86/kvm/x86.c | 20 +++++++++++++-------
> 1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a77b55142c6..60caa3fd40e5 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4326,6 +4326,16 @@ static inline bool kvm_can_mwait_in_guest(void)
> boot_cpu_has(X86_FEATURE_ARAT);
> }
>
> +static u64 kvm_get_allowed_disable_exits(void)
> +{
> + u64 r = KVM_X86_DISABLE_VALID_EXITS;
> +
> + if (!kvm_can_mwait_in_guest())
> + r &= ~KVM_X86_DISABLE_EXITS_MWAIT;
> +
> + return r;
> +}
> +
> static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
> struct kvm_cpuid2 __user *cpuid_arg)
> {
> @@ -4448,10 +4458,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> r = KVM_CLOCK_VALID_FLAGS;
> break;
> case KVM_CAP_X86_DISABLE_EXITS:
> - r |= KVM_X86_DISABLE_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
> - KVM_X86_DISABLE_EXITS_CSTATE;
> - if(kvm_can_mwait_in_guest())
> - r |= KVM_X86_DISABLE_EXITS_MWAIT;
> + r |= kvm_get_allowed_disable_exits();
> break;
> case KVM_CAP_X86_SMM:
> if (!IS_ENABLED(CONFIG_KVM_SMM))
> @@ -6224,15 +6231,14 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
> break;
> case KVM_CAP_X86_DISABLE_EXITS:
> r = -EINVAL;
> - if (cap->args[0] & ~KVM_X86_DISABLE_VALID_EXITS)
> + if (cap->args[0] & ~kvm_get_allowed_disable_exits())
> break;
>
> mutex_lock(&kvm->lock);
> if (kvm->created_vcpus)
> goto disable_exits_unlock;
>
> - if ((cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT) &&
> - kvm_can_mwait_in_guest())
> + if (cap->args[0] & KVM_X86_DISABLE_EXITS_MWAIT)
> kvm->arch.mwait_in_guest = true;
> if (cap->args[0] & KVM_X86_DISABLE_EXITS_HLT)
> kvm->arch.hlt_in_guest = true;
> --
> 2.34.1
>