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From a41340930388022d17c5acfa7c00edc80fa486f6 Mon Sep 17 00:00:00 2001
From: Wei Huang <wei@redhat.com>
Date: Tue, 1 May 2018 09:49:54 -0500
Subject: [PATCH 81/93] KVM: x86: Update cpuid properly when CR4.OSXAVE or
CR4.PKE is changed
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
commit c4d2188206bafa177ea58e9a25b952baa0bf7712 upstream.
The CPUID bits of OSXSAVE (function=0x1) and OSPKE (func=0x7, leaf=0x0)
allows user apps to detect if OS has set CR4.OSXSAVE or CR4.PKE. KVM is
supposed to update these CPUID bits when CR4 is updated. Current KVM
code doesn't handle some special cases when updates come from emulator.
Here is one example:
Step 1: guest boots
Step 2: guest OS enables XSAVE ==> CR4.OSXSAVE=1 and CPUID.OSXSAVE=1
Step 3: guest hot reboot ==> QEMU reset CR4 to 0, but CPUID.OSXAVE==1
Step 4: guest os checks CPUID.OSXAVE, detects 1, then executes xgetbv
Step 4 above will cause an #UD and guest crash because guest OS hasn't
turned on OSXAVE yet. This patch solves the problem by comparing the the
old_cr4 with cr4. If the related bits have been changed,
kvm_update_cpuid() needs to be called.
Signed-off-by: Wei Huang <wei@redhat.com>
Reviewed-by: Bandan Das <bsd@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/x86.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c531231..27e6cf0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7201,6 +7201,7 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
{
struct msr_data apic_base_msr;
int mmu_reset_needed = 0;
+ int cpuid_update_needed = 0;
int pending_vec, max_bits, idx;
struct desc_ptr dt;
@@ -7232,8 +7233,10 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
vcpu->arch.cr0 = sregs->cr0;
mmu_reset_needed |= kvm_read_cr4(vcpu) != sregs->cr4;
+ cpuid_update_needed |= ((kvm_read_cr4(vcpu) ^ sregs->cr4) &
+ (X86_CR4_OSXSAVE | X86_CR4_PKE));
kvm_x86_ops->set_cr4(vcpu, sregs->cr4);
- if (sregs->cr4 & (X86_CR4_OSXSAVE | X86_CR4_PKE))
+ if (cpuid_update_needed)
kvm_update_cpuid(vcpu);
idx = srcu_read_lock(&vcpu->kvm->srcu);
--
2.7.4
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