KVM: VMX: fix vmwrite to invalid VMCS

fpu_activate is called outside of vcpu_load(), which means it should not
touch VMCS, but fpu_activate needs to.  Avoid the call by moving it to a
point where we know that the guest needs eager FPU and VMCS is loaded.

This will get rid of the following trace

 vmwrite error: reg 6800 value 0 (err 1)
  [<ffffffff8162035b>] dump_stack+0x19/0x1b
  [<ffffffffa046c701>] vmwrite_error+0x2c/0x2e [kvm_intel]
  [<ffffffffa045f26f>] vmcs_writel+0x1f/0x30 [kvm_intel]
  [<ffffffffa04617e5>] vmx_fpu_activate.part.61+0x45/0xb0 [kvm_intel]
  [<ffffffffa0461865>] vmx_fpu_activate+0x15/0x20 [kvm_intel]
  [<ffffffffa0560b91>] kvm_arch_vcpu_create+0x51/0x70 [kvm]
  [<ffffffffa0548011>] kvm_vm_ioctl+0x1c1/0x760 [kvm]
  [<ffffffff8118b55a>] ? handle_mm_fault+0x49a/0xec0
  [<ffffffff811e47d5>] do_vfs_ioctl+0x2e5/0x4c0
  [<ffffffff8127abbe>] ? file_has_perm+0xae/0xc0
  [<ffffffff811e4a51>] SyS_ioctl+0xa1/0xc0
  [<ffffffff81630949>] system_call_fastpath+0x16/0x1b

(Note: we also unconditionally activate FPU in vmx_vcpu_reset(), so the
 removed code added nothing.)

Fixes: c447e76b4cab ("kvm/fpu: Enable eager restore kvm FPU for MPX")
Cc: <stable@vger.kernel.org>
Reported-by: Vlastimil Holer <vlastimil.holer@gmail.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 370777daab3f024f1645177039955088e2e9ae73)
OraBug: 25956028
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 1d08ad3582d07fd61cd03302eba547e3a997058b..479dd5eb13072ed8e8e430417c5d6e5aed71c5c3 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -97,7 +97,9 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
        if (best && (best->eax & (F(XSAVES) | F(XSAVEC))))
                best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
 
-       vcpu->arch.eager_fpu = guest_cpuid_has_mpx(vcpu);
+       vcpu->arch.eager_fpu = use_eager_fpu() || guest_cpuid_has_mpx(vcpu);
+       if (vcpu->arch.eager_fpu)
+               kvm_x86_ops->fpu_activate(vcpu);
 
        /*
         * The existing code assumes virtual address is 48-bit in the canonical

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ea306adbbc13603591d46d3f062cc20cf1bc37d1..35b5ec44285ad20752906e9eff00cc05ae8c2cd2 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7087,11 +7087,6 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
 
        vcpu = kvm_x86_ops->vcpu_create(kvm, id);
 
-       /*
-        * Activate fpu unconditionally in case the guest needs eager FPU.  It will be
-        * deactivated soon if it doesn't.
-        */
-       kvm_x86_ops->fpu_activate(vcpu);
        return vcpu;
 }