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Peter Anvin" , Xin Li , Andy Lutomirski , Peter Zijlstra , Andrew Cooper , Tom Lendacky , Nikunj A Dadhania , Shivansh Dhiman , David Woodhouse , Chao Gao , Zhao Liu , Yosry Ahmed , David Matlack , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260911213659.2025974-1-sohil.mehta@intel.com> <20260911213659.2025974-20-sohil.mehta@intel.com> From: Binbin Wu Content-Language: en-US In-Reply-To: <20260911213659.2025974-20-sohil.mehta@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/12/2026 5:36 AM, Sohil Mehta wrote: > From: "Xin Li (Intel)" > > Advertise support for FRED to userspace after changes required to enable > FRED in a KVM guest are in place. > > Signed-off-by: Xin Li (Intel) > Signed-off-by: Sohil Mehta > Reviewed-by: Chao Gao The code change itself looks good to me. But this patch should be moved after patch 25. X86_CR4_FRED is added to nested.msrs.cr4_fixed1 in patch 25, before that if the L1 guest enables FRED, it will break the nested case when do VMXON, which checks nested_host_cr4_valid() and it will fail during the bisect window before patch 25. > --- > v10: > - kvm_cpu_cap_clear(X86_FEATURE_FRED) in svm_set_cpu_caps() (Chao). > --- > arch/x86/kvm/cpuid.c | 1 + > arch/x86/kvm/svm/svm.c | 3 +++ > 2 files changed, 4 insertions(+) > > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index ddb022cb203a..5682bacdfd32 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -1034,6 +1034,7 @@ void kvm_initialize_cpu_caps(void) > F(FSRS), > F(FSRC), > F(WRMSRNS), > + X86_64_F(FRED), > X86_64_F(LKGS), > F(AMX_FP16), > F(AVX_IFMA), > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index f254a5ff570d..dd19c7b4e904 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -5518,6 +5518,9 @@ static __init void svm_set_cpu_caps(void) > > kvm_cpu_cap_clear(X86_FEATURE_IBT); > > + /* SVM FRED virtualization not implemented yet */ > + kvm_cpu_cap_clear(X86_FEATURE_FRED); > + > /* CPUID 0x80000001 and 0x8000000A (SVM features) */ > if (nested) { > kvm_cpu_cap_set(X86_FEATURE_SVM);