linux-kernel - [PATCH 3.16.y-ckt 058/126] KVM: VMX: fix SMEP and SMAP without EPT

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Message-Id: <1449653896-5236-59-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  9 Dec 2015 09:37:08 +0000
From:	Luis Henriques <luis.henriques@...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>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 058/126] KVM: VMX: fix SMEP and SMAP without EPT

3.16.7-ckt21 -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 656ec4a4928a3db7d16e5cb9bce351a478cfd3d5 upstream.

The comment in code had it mostly right, but we enable paging for
emulated real mode regardless of EPT.

Without EPT (which implies emulated real mode), secondary VCPUs won't
start unless we disable SM[AE]P when the guest doesn't use paging.

Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/x86/kvm/vmx.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index aa6bd8cc914c..0502753be5f0 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3523,20 +3523,21 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 		if (!is_paging(vcpu)) {
 			hw_cr4 &= ~X86_CR4_PAE;
 			hw_cr4 |= X86_CR4_PSE;
-			/*
-			 * SMEP/SMAP is disabled if CPU is in non-paging mode
-			 * in hardware. However KVM always uses paging mode to
-			 * emulate guest non-paging mode with TDP.
-			 * To emulate this behavior, SMEP/SMAP needs to be
-			 * manually disabled when guest switches to non-paging
-			 * mode.
-			 */
-			hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP);
 		} else if (!(cr4 & X86_CR4_PAE)) {
 			hw_cr4 &= ~X86_CR4_PAE;
 		}
 	}
 
+	if (!enable_unrestricted_guest && !is_paging(vcpu))
+		/*
+		 * SMEP/SMAP is disabled if CPU is in non-paging mode in
+		 * hardware.  However KVM always uses paging mode without
+		 * unrestricted guest.
+		 * To emulate this behavior, SMEP/SMAP needs to be manually
+		 * disabled when guest switches to non-paging mode.
+		 */
+		hw_cr4 &= ~(X86_CR4_SMEP | X86_CR4_SMAP);
+
 	vmcs_writel(CR4_READ_SHADOW, cr4);
 	vmcs_writel(GUEST_CR4, hw_cr4);
 	return 0;
--
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