linux-kernel - [PATCH 3.19.y-ckt 075/107] KVM: VMX: fix vmwrite to invalid VMCS

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Date:	Wed,  5 Aug 2015 14:49:07 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Radim Krčmář <rkrcmar@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 075/107] KVM: VMX: fix vmwrite to invalid VMCS

3.19.8-ckt5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@...hat.com>

commit 370777daab3f024f1645177039955088e2e9ae73 upstream.

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")
Reported-by: Vlastimil Holer <vlastimil.holer@...il.com>
Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 arch/x86/kvm/cpuid.c | 2 ++
 arch/x86/kvm/x86.c   | 5 -----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 307f9ec..f3e5375 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -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 = 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 4725957..a692f1c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7028,11 +7028,6 @@ 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;
 }
 
-- 
1.9.1

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