linux-kernel - [PATCH v5 6/8] KVM: x86: Allow Guest to set supported bits in XSS

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Message-Id: <20190522070101.7636-7-weijiang.yang@intel.com>
Date:   Wed, 22 May 2019 15:00:59 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     pbonzini@...hat.com, sean.j.christopherson@...el.com,
        mst@...hat.com, rkrcmar@...hat.com, jmattson@...gle.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        yu-cheng.yu@...el.com
Cc:     weijiang.yang@...el.com
Subject: [PATCH v5 6/8] KVM: x86: Allow Guest to set supported bits in XSS

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

Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Co-developed-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/cpuid.c            | 13 ++++++++++---
 arch/x86/kvm/vmx/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 8c3f0ddc7676..035367694056 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -620,6 +620,7 @@ 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 7be16ef0ea4a..b645a143584f 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -122,9 +122,16 @@ 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/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 1c0d487a4037..dec6bda20235 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1945,12 +1945,9 @@ 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,
-- 
2.17.2