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SubjectRe: [PATCH 04/11] KVM: x86: Disable MCE related stuff for TDX
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On 11/13/2021 1:01 AM, Sean Christopherson wrote:
> On Fri, Nov 12, 2021, Xiaoyao Li wrote:
>> From: Sean Christopherson <sean.j.christopherson@intel.com>
>>
>> MCE is not supported for TDX VM and KVM cannot inject #MC to TDX VM.
>>
>> Introduce kvm_guest_mce_disallowed() which actually reports the MCE
>> availability based on vm_type. And use it to guard all the MCE related
>> CAPs and IOCTLs.
>>
>> Note: KVM_X86_GET_MCE_CAP_SUPPORTED is KVM scope so that what it reports
>> may not match the behavior of specific VM (e.g., here for TDX VM). The
>> same for KVM_CAP_MCE when queried from /dev/kvm. To qeuery the precise
>> KVM_CAP_MCE of the VM, it should use VM's fd.
>>
>> [ Xiaoyao: Guard MCE related CAPs ]
>>
>> Co-developed-by: Kai Huang <kai.huang@linux.intel.com>
>> Signed-off-by: Kai Huang <kai.huang@linux.intel.com>
>> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> ---
>> arch/x86/kvm/x86.c | 10 ++++++++++
>> arch/x86/kvm/x86.h | 5 +++++
>> 2 files changed, 15 insertions(+)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index b02088343d80..2b21c5169f32 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -4150,6 +4150,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> break;
>> case KVM_CAP_MCE:
>> r = KVM_MAX_MCE_BANKS;
>> + if (kvm)
>> + r = kvm_guest_mce_disallowed(kvm) ? 0 : r;
>
> r = KVM_MAX_MCE_BANKS;
> if (kvm && kvm_guest_mce_disallowed(kvm))
> r = 0;
>
> or
>
> r = (kvm && kvm_guest_mce_disallowed(kvm)) ? 0 : KVM_MAX_MCE_BANKS;

I will use this one in next submission.

>> break;
>> case KVM_CAP_XCRS:
>> r = boot_cpu_has(X86_FEATURE_XSAVE);
>> @@ -5155,6 +5157,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>> case KVM_X86_SETUP_MCE: {
>> u64 mcg_cap;
>>
>> + r = EINVAL;
>> + if (kvm_guest_mce_disallowed(vcpu->kvm))
>> + goto out;
>> +
>> r = -EFAULT;
>> if (copy_from_user(&mcg_cap, argp, sizeof(mcg_cap)))
>> goto out;
>> @@ -5164,6 +5170,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>> case KVM_X86_SET_MCE: {
>> struct kvm_x86_mce mce;
>>
>> + r = EINVAL;
>> + if (kvm_guest_mce_disallowed(vcpu->kvm))
>> + goto out;
>> +
>> r = -EFAULT;
>> if (copy_from_user(&mce, argp, sizeof(mce)))
>> goto out;
>> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
>> index a2813892740d..69c60297bef2 100644
>> --- a/arch/x86/kvm/x86.h
>> +++ b/arch/x86/kvm/x86.h
>> @@ -441,6 +441,11 @@ static __always_inline bool kvm_irq_injection_disallowed(struct kvm_vcpu *vcpu)
>> return vcpu->kvm->arch.vm_type == KVM_X86_TDX_VM;
>> }
>>
>> +static __always_inline bool kvm_guest_mce_disallowed(struct kvm *kvm)
>
> The "guest" part is potentially confusing and incosistent with e.g.
> kvm_irq_injection_disallowed. And given the current ridiculous spec, CR4.MCE=1
> is _required_, so saying "mce disallowed" is arguably wrong from that perspective.
>
> kvm_mce_injection_disallowed() would be more appropriate.

Good advice, I'll rename to it.

>> +{
>> + return kvm->arch.vm_type == KVM_X86_TDX_VM;
>> +}
>> +
>> void kvm_load_guest_xsave_state(struct kvm_vcpu *vcpu);
>> void kvm_load_host_xsave_state(struct kvm_vcpu *vcpu);
>> int kvm_spec_ctrl_test_value(u64 value);
>> --
>> 2.27.0
>>

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