[v6,07/12] KVM: x86: Refresh CPUID on writes to MSR_IA32_XSS

Commit Message

Yang, Weijiang July 16, 2021, 8:50 a.m. UTC

Updated CPUID.0xD.0x1, which reports the current required storage size
of all features enabled via XCR0 | XSS, when the guest's XSS is modified.

Note, KVM does not yet support any XSS based features, i.e. supported_xss
is guaranteed to be zero at this time.

Co-developed-by: Zhang Yi Z <[e-mail]>
Signed-off-by: Zhang Yi Z <[e-mail]>
Signed-off-by: Yang Weijiang <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/cpuid.c            | 21 ++++++++++++++++++---
 arch/x86/kvm/x86.c              |  7 +++++--
 3 files changed, 24 insertions(+), 5 deletions(-)

Patch

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9c7ced0e3171..a98b15cefc6b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -651,6 +651,7 @@  struct kvm_vcpu_arch {
 
 	u64 xcr0;
 	u64 guest_supported_xcr0;
+	u64 guest_supported_xss;
 
 	struct kvm_pio_request pio;
 	void *pio_data;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b4da665bb892..d6e343809b25 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -131,9 +131,24 @@  void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
 		best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
 
 	best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
-	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
-		     cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
-		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
+	if (best) {
+		if (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
+		    cpuid_entry_has(best, X86_FEATURE_XSAVEC))  {
+			u64 xstate = vcpu->arch.xcr0 | vcpu->arch.ia32_xss;
+
+			best->ebx = xstate_required_size(xstate, true);
+		}
+
+		if (!cpuid_entry_has(best, X86_FEATURE_XSAVES)) {
+			best->ecx = 0;
+			best->edx = 0;
+		}
+		vcpu->arch.guest_supported_xss =
+			(((u64)best->edx << 32) | best->ecx) & supported_xss;
+
+	} else {
+		vcpu->arch.guest_supported_xss = 0;
+	}
 
 	best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
 	if (kvm_hlt_in_guest(vcpu->kvm) && best &&
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b586a45fce2b..5f2e13c9f507 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3265,9 +3265,12 @@  int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		 * IA32_XSS[bit 8]. Guests have to use RDMSR/WRMSR rather than
 		 * XSAVES/XRSTORS to save/restore PT MSRs.
 		 */
-		if (data & ~supported_xss)
+		if (data & ~vcpu->arch.guest_supported_xss)
 			return 1;
-		vcpu->arch.ia32_xss = data;
+		if (vcpu->arch.ia32_xss != data) {
+			vcpu->arch.ia32_xss = data;
+			kvm_update_cpuid_runtime(vcpu);
+		}
 		break;
 	case MSR_SMI_COUNT:
 		if (!msr_info->host_initiated)