3.16.60-rc1 review patch. If anyone has any objections, please let me know.
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From: Wei Huang wei@redhat.com
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 Signed-off-by: Radim Krčmář rkrcmar@redhat.com [bwh: Backported to 3.16: PKE is not supported] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/x86/kvm/x86.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6668,6 +6668,7 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct { 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;
@@ -6702,8 +6703,10 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct 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); kvm_x86_ops->set_cr4(vcpu, sregs->cr4); - if (sregs->cr4 & X86_CR4_OSXSAVE) + if (cpuid_update_needed) kvm_update_cpuid(vcpu);
idx = srcu_read_lock(&vcpu->kvm->srcu);