2022-06-15 01:29:51

by Kechen Lu

Subject: [RFC PATCH v3 3/7] KVM: x86: Reject disabling of MWAIT interception when not allowed

From: Sean Christopherson <[email protected]>

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 APIC timer.

Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT intercepts")
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/x86.c | 21 ++++++++++++++-------
1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b419b258ed90..f31ebbb1b94f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4199,6 +4199,17 @@ 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_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
+ KVM_X86_DISABLE_EXITS_CSTATE;
+
+ 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)
{
@@ -4318,10 +4329,7 @@ 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:
/* SMBASE is usually relocated above 1M on modern chipsets,
@@ -6003,15 +6011,14 @@ 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;
--
2.32.0

2022-07-20 17:35:59

by Sean Christopherson

Subject: Re: [RFC PATCH v3 3/7] KVM: x86: Reject disabling of MWAIT interception when not allowed

On Tue, Jun 14, 2022, Kechen Lu wrote:
> From: Sean Christopherson <[email protected]>
>
> 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 APIC timer.
>
> Fixes: 4d5422cea3b6 ("KVM: X86: Provide a capability to disable MWAIT intercepts")
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> arch/x86/kvm/x86.c | 21 ++++++++++++++-------
> 1 file changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b419b258ed90..f31ebbb1b94f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4199,6 +4199,17 @@ 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_EXITS_HLT | KVM_X86_DISABLE_EXITS_PAUSE |
> + KVM_X86_DISABLE_EXITS_CSTATE;
> +
> + if(kvm_can_mwait_in_guest())

Probably my fault for not fixing this during copy+paste, but add a space after the if, i.e.

if (kvm_can_mwait_in_guest())

> + r |= KVM_X86_DISABLE_EXITS_MWAIT;
> +
> + return r;
> +}