linux-kernel - [RFC PATCH v4 6/8] KVM:x86: Allow Guest to set supported bits in XSS

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Message-Id: <20190318150351.15550-7-weijiang.yang@intel.com>
Date:   Mon, 18 Mar 2019 23:03:49 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     pbonzini@...hat.com, kvm@...r.kernel.org, mst@...hat.com,
        rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, yu-cheng.yu@...el.com
Cc:     Yang Weijiang <weijiang.yang@...el.com>,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: [RFC PATCH v4 6/8] KVM:x86: Allow Guest to set supported bits in XSS

Now that KVM supports setting CET related bits.
Previously, KVM did not support setting any bits in XSS
and so hardcoded its check to inject a #GP if Guest
attempted to write a non-zero value to IA32_XSS.

Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/cpuid.c            | 13 ++++++++++---
 arch/x86/kvm/vmx.c              |  7 ++-----
 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 fc038bf1924a..30dfb5a65d1b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -616,6 +616,7 @@ 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 29d6a5cdc746..e66a0557899c 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -125,9 +125,16 @@ 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 |
-			    kvm_supported_xss(), true);
+	if (best) {
+		if (best->eax & (F(XSAVES) | F(XSAVEC)))
+			best->ebx = xstate_required_size(vcpu->arch.xcr0 |
+				    kvm_supported_xss(), true);
+
+		vcpu->arch.guest_supported_xss = best->ecx &
+			kvm_supported_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.c b/arch/x86/kvm/vmx.c
index 246467c12930..816e11a66557 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4327,12 +4327,9 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_IA32_XSS:
 		if (!vmx_xsaves_supported())
 			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)
 			add_atomic_switch_msr(vmx, MSR_IA32_XSS,
-- 
2.17.1