On 18/1/2022 1:31 am, Paolo Bonzini wrote:
On 1/17/22 08:45, Like Xu wrote:
From: Like Xu <likexu@xxxxxxxxxxx>
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@xxxxxxxxxxx>
---
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
