linux-kernel - [PATCH] kvm, vmx: Really fix lazy FPU on nested guest

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Date:	Thu, 27 Feb 2014 23:01:06 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kchamart@...hat.com, stefan.bader@...onical.com,
	bourgeois@...tin.fr, kvm@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH] kvm, vmx: Really fix lazy FPU on nested guest

Commit e504c9098ed6 (kvm, vmx: Fix lazy FPU on nested guest, 2013-11-13)
highlighted a real problem, but the fix was subtly wrong.

nested_read_cr0 is the CR0 as read by L2, but here we want to look at
the CR0 value reflecting L1's setup.  In other words, L2 might think
that TS=0 (so nested_read_cr0 has the bit clear); but if L1 is actually
running it with TS=1, we should inject the fault into L1.

The effective value of CR0 in L2 is contained in vmcs12->guest_cr0, use
it.

Fixes: e504c9098ed6acd9e1079c5e10e4910724ad429f
Reported-by: Kashyap Chamarty <kchamart@...hat.com>
Reported-by: Stefan Bader <stefan.bader@...onical.com>
Tested-by: Kashyap Chamarty <kchamart@...hat.com>
Tested-by: Anthoine Bourgeois <bourgeois@...tin.fr>
Cc: stable@...r.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/vmx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index a06f101ef64b..392752834751 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -6688,7 +6688,7 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
 		else if (is_page_fault(intr_info))
 			return enable_ept;
 		else if (is_no_device(intr_info) &&
-			 !(nested_read_cr0(vmcs12) & X86_CR0_TS))
+			 !(vmcs12->guest_cr0 & X86_CR0_TS))
 			return 0;
 		return vmcs12->exception_bitmap &
 				(1u << (intr_info & INTR_INFO_VECTOR_MASK));
-- 
1.8.3.1

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