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From: Like Xu <>
To: Paolo Bonzini <>
Cc: Jing Liu <>,
	Sean Christopherson <>,
	Jim Mattson <>,
	Vitaly Kuznetsov <>,
	Wanpeng Li <>,
	Joerg Roedel <>,,
Subject: [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing
Date: Mon, 17 Jan 2022 15:45:31 +0800	[thread overview]
Message-ID: <> (raw)

From: Like Xu <>

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 <>
 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)
+			if (!kvm_cpu_cap_has(X86_FEATURE_XFD))
+				entry->ecx &= ~BIT_ULL(2);
 			entry->edx = 0;

             reply	other threads:[~2022-01-17  7:45 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-17  7:45 Like Xu [this message]
2022-01-17 17:31 ` [PATCH] KVM: x86/cpuid: Clear XFD for component i if the base feature is missing Paolo Bonzini
2022-01-18  6:43   ` Like Xu
2022-01-18  8:42     ` Paolo Bonzini

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