From: Sean Christopherson seanjc@google.com Sent: Wednesday, January 5, 2022 3:33 AM
On Wed, Dec 29, 2021, Yang Zhong wrote:
From: Jing Liu jing2.liu@intel.com
Intel's eXtended Feature Disable (XFD) feature allows the software to dynamically adjust fpstate buffer size for XSAVE features which have large state.
Because fpstate has been expanded for all possible dynamic xstates at KVM_SET_CPUID2, emulation of the IA32_XFD MSR is straightforward. For write just call fpu_update_guest_xfd() to update the guest fpu container once all the sanity checks are passed. For read then return the cached value in the container.
Signed-off-by: Zeng Guang guang.zeng@intel.com Signed-off-by: Wei Wang wei.w.wang@intel.com Signed-off-by: Jing Liu jing2.liu@intel.com Signed-off-by: Yang Zhong yang.zhong@intel.com
arch/x86/kvm/x86.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index e50e97ac4408..36677b754ac9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1359,6 +1359,7 @@ static const u32 msrs_to_save_all[] = { MSR_F15H_PERF_CTL3, MSR_F15H_PERF_CTL4,
MSR_F15H_PERF_CTL5,
MSR_F15H_PERF_CTR0, MSR_F15H_PERF_CTR1,
MSR_F15H_PERF_CTR2,
MSR_F15H_PERF_CTR3, MSR_F15H_PERF_CTR4,
MSR_F15H_PERF_CTR5,
- MSR_IA32_XFD,
};
static u32 msrs_to_save[ARRAY_SIZE(msrs_to_save_all)]; @@ -3669,6 +3670,19 @@ int kvm_set_msr_common(struct kvm_vcpu
*vcpu, struct msr_data *msr_info)
return 1; vcpu->arch.msr_misc_features_enables = data; break;+#ifdef CONFIG_X86_64
- case MSR_IA32_XFD:
if (!msr_info->host_initiated &&!guest_cpuid_has(vcpu, X86_FEATURE_XFD))return 1;if (data & ~(XFEATURE_MASK_USER_DYNAMIC &vcpu->arch.guest_supported_xcr0))return 1;fpu_update_guest_xfd(&vcpu->arch.guest_fpu, data);break;+#endif default: if (kvm_pmu_is_valid_msr(vcpu, msr)) return kvm_pmu_set_msr(vcpu, msr_info); @@ -3989,6 +4003,15 @@ int kvm_get_msr_common(struct kvm_vcpu
*vcpu, struct msr_data *msr_info)
case MSR_K7_HWCR: msr_info->data = vcpu->arch.msr_hwcr; break; +#ifdef CONFIG_X86_64
- case MSR_IA32_XFD:
if (!msr_info->host_initiated &&!guest_cpuid_has(vcpu, X86_FEATURE_XFD))return 1;msr_info->data = vcpu->arch.guest_fpu.fpstate->xfd;break;+#endif default: if (kvm_pmu_is_valid_msr(vcpu, msr_info->index)) return kvm_pmu_get_msr(vcpu, msr_info); @@ -6422,6 +6445,10 @@ static void kvm_init_msr_list(void) min(INTEL_PMC_MAX_GENERIC,
x86_pmu.num_counters_gp))
continue; break;
case MSR_IA32_XFD:if (!kvm_cpu_cap_has(X86_FEATURE_XFD))continue;I suspect the 32-bit host support is wrong. The kernel's handle_xfd_event() checks for 64-bit support in addition to the CPU feature itself, which implies that the feature can be reported in boot_cpu_data for 32-bit kernels.
static bool handle_xfd_event(struct pt_regs *regs) { u64 xfd_err; int err;
if (!IS_ENABLED(CONFIG_X86_64) || !cpu_feature_enabled(X86_FEATURE_XFD)) return false;
... }
In this specific case, that means KVM will tell userspace it needs to mgirate MSR_IA32_XFD, and then reject attempts to read/write the MSR.
If 32-bit host kernels do not explicitly suppress X86_FEATURE_XFD, then KVM
I didn't find explicit suppress
needs to do:
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 556555537a18..156ce332d55b 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -455,9 +455,11 @@ void kvm_set_cpu_caps(void) #ifdef CONFIG_X86_64 unsigned int f_gbpages = F(GBPAGES); unsigned int f_lm = F(LM);
unsigned int f_xfd = F(XFD);#else unsigned int f_gbpages = 0; unsigned int f_lm = 0;
unsigned int f_xfd = 0;#endif memset(kvm_cpu_caps, 0, sizeof(kvm_cpu_caps));
@@ -545,7 +547,7 @@ void kvm_set_cpu_caps(void) );
kvm_cpu_cap_mask(CPUID_D_1_EAX,
F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | F(XSAVES) | F(XFD)
F(XSAVEOPT) | F(XSAVEC) | F(XGETBV1) | F(XSAVES) | f_xfd ); kvm_cpu_cap_init_scattered(CPUID_12_EAX,
so this change makes sense. will incorporate it in next version.
Thanks Kevin