Re: [PATCH v2] KVM: VMX: disable SMEP feature when guest is in non-paging mode

2013-02-05 Thread Marcelo Tosatti 
On Mon, Feb 04, 2013 at 11:50:43AM +0800, Dongxiao Xu wrote:
 Changes from v1 to v2:
  - Modify commit message and comments according to Gleb's suggestions.
 
 SMEP 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 needs to be manually
 disabled when guest switches to non-paging mode.
 
 We met an issue that, SMP Linux guest with recent kernel (enable
 SMEP support, for example, 3.5.3) would crash with triple fault if
 setting unrestricted_guest=0. This is because KVM uses an identity
 mapping page table to emulate the non-paging mode, where the page
 table is set with USER flag. If SMEP is still enabled in this case,
 guest will meet unhandlable page fault and then crash.
 
 Signed-off-by: Dongxiao Xu dongxiao...@intel.com
 Signed-off-by: Xiantao Zhang xiantao.zh...@intel.com
 ---
  arch/x86/kvm/vmx.c |8 
  1 files changed, 8 insertions(+), 0 deletions(-)

Applied, thanks.

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[PATCH v2] KVM: VMX: disable SMEP feature when guest is in non-paging mode

2013-02-03 Thread Dongxiao Xu 
Changes from v1 to v2:
 - Modify commit message and comments according to Gleb's suggestions.

SMEP 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 needs to be manually
disabled when guest switches to non-paging mode.

We met an issue that, SMP Linux guest with recent kernel (enable
SMEP support, for example, 3.5.3) would crash with triple fault if
setting unrestricted_guest=0. This is because KVM uses an identity
mapping page table to emulate the non-paging mode, where the page
table is set with USER flag. If SMEP is still enabled in this case,
guest will meet unhandlable page fault and then crash.

Signed-off-by: Dongxiao Xu dongxiao...@intel.com
Signed-off-by: Xiantao Zhang xiantao.zh...@intel.com
---
 arch/x86/kvm/vmx.c |8 
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 9120ae1..70393e2 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3155,6 +3155,14 @@ 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 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 needs to be manually
+* disabled when guest switches to non-paging mode.
+*/
+   hw_cr4 = ~X86_CR4_SMEP;
} else if (!(cr4  X86_CR4_PAE)) {
hw_cr4 = ~X86_CR4_PAE;
}
-- 
1.7.1

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