Commit 370777da authored Jul 03, 2015 by Radim Krčmář Committed by Paolo Bonzini Jul 10, 2015

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: c447e76b ("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>

parent d1fe9219

arch/x86/kvm/cpuid.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -98,6 +98,8 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);

		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

arch/x86/kvm/x86.c

+0 −5

Original line number	Diff line number	Diff line
		@@ -7315,11 +7315,6 @@ 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;
		}

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