* [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing
@ 2022-01-17 7:45 Like Xu
2022-01-17 17:31 ` Paolo Bonzini
0 siblings, 1 reply; 4+ messages in thread
From: Like Xu @ 2022-01-17 7:45 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Jing Liu, Sean Christopherson, Jim Mattson, Vitaly Kuznetsov,
Wanpeng Li, Joerg Roedel, kvm, linux-kernel
From: Like Xu <likexu@tencent.com>
According to Intel extended feature disable (XFD) spec, the sub-function i
(i > 1) of CPUID function 0DH enumerates "details for state component i.
ECX[2] enumerates support for XFD support for this state component."
If KVM does not report F(XFD) feature (e.g. due to CONFIG_X86_64),
then the corresponding XFD support for any state component i
should also be removed. Translate this dependency into KVM terms.
Fixes: 690a757d610e ("kvm: x86: Add CPUID support for Intel AMX")
Signed-off-by: Like Xu <likexu@tencent.com>
---
arch/x86/kvm/cpuid.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index c55e57b30e81..e96efef4f048 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -886,6 +886,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
--array->nent;
continue;
}
+
+ if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
+ entry->ecx &= ~BIT_ULL(2);
entry->edx = 0;
}
break;
--
2.33.1
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing
2022-01-17 7:45 [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing Like Xu
@ 2022-01-17 17:31 ` Paolo Bonzini
2022-01-18 6:43 ` Like Xu
0 siblings, 1 reply; 4+ messages in thread
From: Paolo Bonzini @ 2022-01-17 17:31 UTC (permalink / raw)
To: Like Xu
Cc: Jing Liu, Sean Christopherson, Jim Mattson, Vitaly Kuznetsov,
Wanpeng Li, Joerg Roedel, kvm, linux-kernel
On 1/17/22 08:45, Like Xu wrote:
> From: Like Xu <likexu@tencent.com>
>
> According to Intel extended feature disable (XFD) spec, the sub-function i
> (i > 1) of CPUID function 0DH enumerates "details for state component i.
> ECX[2] enumerates support for XFD support for this state component."
>
> If KVM does not report F(XFD) feature (e.g. due to CONFIG_X86_64),
> then the corresponding XFD support for any state component i
> should also be removed. Translate this dependency into KVM terms.
>
> Fixes: 690a757d610e ("kvm: x86: Add CPUID support for Intel AMX")
> Signed-off-by: Like Xu <likexu@tencent.com>
> ---
> arch/x86/kvm/cpuid.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index c55e57b30e81..e96efef4f048 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -886,6 +886,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> --array->nent;
> continue;
> }
> +
> + if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
> + entry->ecx &= ~BIT_ULL(2);
> entry->edx = 0;
> }
> break;
Generally this is something that is left to userspace. Apart from the
usecase of "call KVM_GET_SUPPORTED_CPUID and pass it to KVM_SET_CPUID2",
userspace should know what any changed bits mean.
Paolo
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing
2022-01-17 17:31 ` Paolo Bonzini
@ 2022-01-18 6:43 ` Like Xu
2022-01-18 8:42 ` Paolo Bonzini
0 siblings, 1 reply; 4+ messages in thread
From: Like Xu @ 2022-01-18 6:43 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Jing Liu, Sean Christopherson, Jim Mattson, Vitaly Kuznetsov,
Wanpeng Li, Joerg Roedel, kvm, linux-kernel
On 18/1/2022 1:31 am, Paolo Bonzini wrote:
> On 1/17/22 08:45, Like Xu wrote:
>> From: Like Xu <likexu@tencent.com>
>>
>> According to Intel extended feature disable (XFD) spec, the sub-function i
>> (i > 1) of CPUID function 0DH enumerates "details for state component i.
>> ECX[2] enumerates support for XFD support for this state component."
>>
>> If KVM does not report F(XFD) feature (e.g. due to CONFIG_X86_64),
>> then the corresponding XFD support for any state component i
>> should also be removed. Translate this dependency into KVM terms.
>>
>> Fixes: 690a757d610e ("kvm: x86: Add CPUID support for Intel AMX")
>> Signed-off-by: Like Xu <likexu@tencent.com>
>> ---
>> arch/x86/kvm/cpuid.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index c55e57b30e81..e96efef4f048 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -886,6 +886,9 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array
>> *array, u32 function)
>> --array->nent;
>> continue;
>> }
>> +
>> + if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
>> + entry->ecx &= ~BIT_ULL(2);
>> entry->edx = 0;
>> }
>> break;
>
> Generally this is something that is left to userspace. Apart from the usecase
> of "call KVM_GET_SUPPORTED_CPUID and pass it to KVM_SET_CPUID2", userspace
> should know what any changed bits mean.
>
> Paolo
>
I totally agree that setting the appropriate CPUID bits for a feature is a user
space thing.
But this patch is more focused on fixing a different type of problem, which is
that the capabilities exposed by KVM should not *contradict each other* :
a user space may be confused with the current code base :
- why KVM does not have F(XFD) feature (MSR_IA32_XFD and XFD_ERR non-exit),
- but KVM reports XFD support for state component i individually;
This is like KVM reporting PEBS when no PMU capacity is reported (due to module
param).
Does this clarification help ?
Thanks,
Like Xu
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing
2022-01-18 6:43 ` Like Xu
@ 2022-01-18 8:42 ` Paolo Bonzini
0 siblings, 0 replies; 4+ messages in thread
From: Paolo Bonzini @ 2022-01-18 8:42 UTC (permalink / raw)
To: Like Xu
Cc: Jing Liu, Sean Christopherson, Jim Mattson, Vitaly Kuznetsov,
Wanpeng Li, Joerg Roedel, kvm, linux-kernel
On 1/18/22 07:43, Like Xu wrote:
> On 18/1/2022 1:31 am, Paolo Bonzini wrote:
>> On 1/17/22 08:45, Like Xu wrote:
>>> From: Like Xu <likexu@tencent.com>
>>>
>>> According to Intel extended feature disable (XFD) spec, the
>>> sub-function i
>>> (i > 1) of CPUID function 0DH enumerates "details for state component i.
>>> ECX[2] enumerates support for XFD support for this state component."
>>>
>>> If KVM does not report F(XFD) feature (e.g. due to CONFIG_X86_64),
>>> then the corresponding XFD support for any state component i
>>> should also be removed. Translate this dependency into KVM terms.
>>>
>>> Fixes: 690a757d610e ("kvm: x86: Add CPUID support for Intel AMX")
>>> Signed-off-by: Like Xu <likexu@tencent.com>
>>> ---
>>> arch/x86/kvm/cpuid.c | 3 +++
>>> 1 file changed, 3 insertions(+)
>>>
>>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>>> index c55e57b30e81..e96efef4f048 100644
>>> --- a/arch/x86/kvm/cpuid.c
>>> +++ b/arch/x86/kvm/cpuid.c
>>> @@ -886,6 +886,9 @@ static inline int __do_cpuid_func(struct
>>> kvm_cpuid_array *array, u32 function)
>>> --array->nent;
>>> continue;
>>> }
>>> +
>>> + if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
>>> + entry->ecx &= ~BIT_ULL(2);
>>> entry->edx = 0;
>>> }
>>> break;
>>
>> Generally this is something that is left to userspace. Apart from the
>> usecase of "call KVM_GET_SUPPORTED_CPUID and pass it to
>> KVM_SET_CPUID2", userspace should know what any changed bits mean.
>>
>> Paolo
>>
>
> I totally agree that setting the appropriate CPUID bits for a feature is
> a user space thing.
>
> But this patch is more focused on fixing a different type of problem,
> which is
> that the capabilities exposed by KVM should not *contradict each other* :
>
> a user space may be confused with the current code base :
> - why KVM does not have F(XFD) feature (MSR_IA32_XFD and XFD_ERR
> non-exit),
> - but KVM reports XFD support for state component i individually;
Got it. Yeah, the patch makes sense for the sake of CONFIG_X86_64.
Paolo
> This is like KVM reporting PEBS when no PMU capacity is reported (due to
> module param).
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-01-18 8:42 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-01-17 7:45 [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing Like Xu
2022-01-17 17:31 ` Paolo Bonzini
2022-01-18 6:43 ` Like Xu
2022-01-18 8:42 ` Paolo Bonzini
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).