linux-kernel - [PATCH 4.2.y-ckt 038/206] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu

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Message-Id: <1465507015-23052-39-git-send-email-kamal@canonical.com>
Date:	Thu,  9 Jun 2016 14:14:07 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Bruce Rogers <brogers@...e.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 4.2.y-ckt 038/206] KVM: x86: fix ordering of cr0 initialization code in vmx_cpu_reset

4.2.8-ckt12 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Bruce Rogers <brogers@...e.com>

commit f24632475d4ffed5626abbfab7ef30a128dd1474 upstream.

Commit d28bc9dd25ce reversed the order of two lines which initialize cr0,
allowing the current (old) cr0 value to mess up vcpu initialization.
This was observed in the checks for cr0 X86_CR0_WP bit in the context of
kvm_mmu_reset_context(). Besides, setting vcpu->arch.cr0 after vmx_set_cr0()
is completely redundant. Change the order back to ensure proper vcpu
initialization.

The combination of booting with ovmf firmware when guest vcpus > 1 and kvm's
ept=N option being set results in a VM-entry failure. This patch fixes that.

Fixes: d28bc9dd25ce ("KVM: x86: INIT and reset sequences are different")
Signed-off-by: Bruce Rogers <brogers@...e.com>
Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.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 c832c7d..8f30efc 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4795,8 +4795,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 		vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
 
 	cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET;
-	vmx_set_cr0(vcpu, cr0); /* enter rmode */
 	vmx->vcpu.arch.cr0 = cr0;
+	vmx_set_cr0(vcpu, cr0); /* enter rmode */
 	vmx_set_cr4(vcpu, 0);
 	vmx_set_efer(vcpu, 0);
 	vmx_fpu_activate(vcpu);
-- 
2.7.4