[PATCH v7 5/7] kvm: x86: Add CET CR4 bit and XSS support

[Yang Weijiang]

CR4.CET(bit 23) is master enable bit for CET feature.
Previously, KVM did not support setting any bits in XSS
so it's hardcoded to check and inject a #GP if Guest
attempted to write a non-zero value to XSS, now it supports
CET related bits setting.

Co-developed-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h |  4 +++-
 arch/x86/kvm/cpuid.c            | 11 +++++++++--
 arch/x86/kvm/vmx/vmx.c          |  6 +-----
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d018df8c5f32..8f97269d6d9f 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -90,7 +90,8 @@
 			  | X86_CR4_PGE | X86_CR4_PCE | X86_CR4_OSFXSR | X86_CR4_PCIDE \
 			  | X86_CR4_OSXSAVE | X86_CR4_SMEP | X86_CR4_FSGSBASE \
 			  | X86_CR4_OSXMMEXCPT | X86_CR4_LA57 | X86_CR4_VMXE \
-			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP))
+			  | X86_CR4_SMAP | X86_CR4_PKE | X86_CR4_UMIP \
+			  | X86_CR4_CET))
 
 #define CR8_RESERVED_BITS (~(unsigned long)X86_CR8_TPR)
 
@@ -623,6 +624,7 @@ struct kvm_vcpu_arch {
 
 	u64 xcr0;
 	u64 guest_supported_xcr0;
+	u64 guest_supported_xss;
 	u32 guest_xstate_size;
 
 	struct kvm_pio_request pio;
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0a47b9e565be..dd3ddc6daa58 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -120,8 +120,15 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 	}
 
 	best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
-	if (best && (best->eax & (F(XSAVES) | F(XSAVEC))))
-		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
+	if (best && (best->eax & (F(XSAVES) | F(XSAVEC)))) {
+		u64 kvm_xss = kvm_supported_xss();
+
+		best->ebx =
+			xstate_required_size(vcpu->arch.xcr0 | kvm_xss, true);
+		vcpu->arch.guest_supported_xss = best->ecx & kvm_xss;
+	} else {
+		vcpu->arch.guest_supported_xss = 0;
+	}
 
 	/*
 	 * The existing code assumes virtual address is 48-bit or 57-bit in the
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index ba1a83d11e69..44913e4ab558 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1973,11 +1973,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		     !(guest_cpuid_has(vcpu, X86_FEATURE_XSAVE) &&
 		       guest_cpuid_has(vcpu, X86_FEATURE_XSAVES))))
 			return 1;
-		/*
-		 * The only supported bit as of Skylake is bit 8, but
-		 * it is not supported on KVM.
-		 */
-		if (data != 0)
+		if (data & ~vcpu->arch.guest_supported_xss)
 			return 1;
 		vcpu->arch.ia32_xss = data;
 		if (vcpu->arch.ia32_xss != host_xss)
-- 
2.17.2