[Qemu-devel] [PATCH v3 1/4] KVM/X86: Fix xsave cpuid exposing bug

[Liu, Jinsong]

>From 3155a190ce6ebb213e6c724240f4e6620ba67a9d Mon Sep 17 00:00:00 2001
From: Liu Jinsong <address@hidden>
Date: Fri, 13 Dec 2013 02:32:03 +0800
Subject: [PATCH v3 1/4] KVM/X86: Fix xsave cpuid exposing bug

EBX of cpuid(0xD, 0) is dynamic per XCR0 features enable/disable.
Bit 63 of XCR0 is reserved for future expansion.

Signed-off-by: Liu Jinsong <address@hidden>
---
 arch/x86/include/asm/xsave.h |    2 ++
 arch/x86/kvm/cpuid.c         |    6 +++---
 arch/x86/kvm/x86.c           |    7 +++++--
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/xsave.h b/arch/x86/include/asm/xsave.h
index 5547389..f6c4e85 100644
--- a/arch/x86/include/asm/xsave.h
+++ b/arch/x86/include/asm/xsave.h
@@ -13,6 +13,8 @@
 #define XSTATE_BNDCSR  0x10
 
 #define XSTATE_FPSSE   (XSTATE_FP | XSTATE_SSE)
+/* Bit 63 of XCR0 is reserved for future expansion */
+#define XSTATE_EXTEND_MASK     (~(XSTATE_FPSSE | (1 << 63)))
 
 #define FXSAVE_SIZE    512
 
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index c697625..2d661e6 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -28,7 +28,7 @@ static u32 xstate_required_size(u64 xstate_bv)
        int feature_bit = 0;
        u32 ret = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
 
-       xstate_bv &= ~XSTATE_FPSSE;
+       xstate_bv &= XSTATE_EXTEND_MASK;
        while (xstate_bv) {
                if (xstate_bv & 0x1) {
                        u32 eax, ebx, ecx, edx;
@@ -74,8 +74,8 @@ void kvm_update_cpuid(struct kvm_vcpu *vcpu)
                vcpu->arch.guest_supported_xcr0 =
                        (best->eax | ((u64)best->edx << 32)) &
                        host_xcr0 & KVM_SUPPORTED_XCR0;
-               vcpu->arch.guest_xstate_size =
-                       xstate_required_size(vcpu->arch.guest_supported_xcr0);
+               vcpu->arch.guest_xstate_size = best->ebx =
+                       xstate_required_size(vcpu->arch.xcr0);
        }
 
        kvm_pmu_cpuid_update(vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 21ef1ba..1657ca2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -576,13 +576,13 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
 
 int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 {
-       u64 xcr0;
+       u64 xcr0 = xcr;
+       u64 old_xcr0 = vcpu->arch.xcr0;
        u64 valid_bits;
 
        /* Only support XCR_XFEATURE_ENABLED_MASK(xcr0) now  */
        if (index != XCR_XFEATURE_ENABLED_MASK)
                return 1;
-       xcr0 = xcr;
        if (!(xcr0 & XSTATE_FP))
                return 1;
        if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE))
@@ -599,6 +599,9 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 
        kvm_put_guest_xcr0(vcpu);
        vcpu->arch.xcr0 = xcr0;
+
+       if ((xcr0 ^ old_xcr0) & XSTATE_EXTEND_MASK)
+               kvm_update_cpuid(vcpu);
        return 0;
 }
 
-- 
1.7.1