Commit 779ed055 authored by Yang Weijiang's avatar Yang Weijiang Committed by Sean Christopherson
Browse files

KVM: x86: Initialize kvm_caps.supported_xss 



Set original kvm_caps.supported_xss to (host_xss & KVM_SUPPORTED_XSS) if
XSAVES is supported. host_xss contains the host supported xstate feature
bits for thread FPU context switch, KVM_SUPPORTED_XSS includes all KVM
enabled XSS feature bits, the resulting value represents the supervisor
xstates that are available to guest and are backed by host FPU framework
for swapping {guest,host} XSAVE-managed registers/MSRs.

[sean: relocate and enhance comment about PT / XSS[8] ]

Signed-off-by: default avatarYang Weijiang <weijiang.yang@intel.com>
Reviewed-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: default avatarChao Gao <chao.gao@intel.com>
Tested-by: default avatarMathias Krause <minipli@grsecurity.net>
Tested-by: default avatarJohn Allen <john.allen@amd.com>
Tested-by: default avatarRick Edgecombe <rick.p.edgecombe@intel.com>
Reviewed-by: default avatarXiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: default avatarChao Gao <chao.gao@intel.com>
Reviewed-by: default avatarBinbin Wu <binbin.wu@linux.intel.com>
Link: https://lore.kernel.org/r/20250919223258.1604852-9-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 9622e116

arch/x86/kvm/x86.c

+15 −8
Original line number Diff line number Diff line
@@ -217,6 +217,14 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs; 
				| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \

				| XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)



/*

 * Note, KVM supports exposing PT to the guest, but does not support context

 * switching PT via XSTATE (KVM's PT virtualization relies on perf; swapping

 * PT via guest XSTATE would clobber perf state), i.e. KVM doesn't support

 * IA32_XSS[bit 8] (guests can/must use RDMSR/WRMSR to save/restore PT MSRs).

 */

#define KVM_SUPPORTED_XSS     0



bool __read_mostly allow_smaller_maxphyaddr = 0;

EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
@@ -3986,11 +3994,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 
	case MSR_IA32_XSS:

		if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))

			return KVM_MSR_RET_UNSUPPORTED;

		/*

		 * KVM supports exposing PT to the guest, but does not support

		 * IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than

		 * XSAVES/XRSTORS to save/restore PT MSRs.

		 */



		if (data & ~vcpu->arch.guest_supported_xss)

			return 1;

		if (vcpu->arch.ia32_xss == data)
@@ -9822,14 +9826,17 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops) 
		kvm_host.xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);

		kvm_caps.supported_xcr0 = kvm_host.xcr0 & KVM_SUPPORTED_XCR0;

	}



	if (boot_cpu_has(X86_FEATURE_XSAVES)) {

		rdmsrq(MSR_IA32_XSS, kvm_host.xss);

		kvm_caps.supported_xss = kvm_host.xss & KVM_SUPPORTED_XSS;

	}



	kvm_caps.supported_quirks = KVM_X86_VALID_QUIRKS;

	kvm_caps.inapplicable_quirks = KVM_X86_CONDITIONAL_QUIRKS;



	rdmsrq_safe(MSR_EFER, &kvm_host.efer);



	if (boot_cpu_has(X86_FEATURE_XSAVES))

		rdmsrq(MSR_IA32_XSS, kvm_host.xss);



	kvm_init_pmu_capability(ops->pmu_ops);



	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))