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KVM: VMX: disable SMEP feature when guest is in non-paging mode 

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.

Reviewed-by: Gleb Natapov <gleb@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Dongxiao Xu 2013-02-04 11:50:43 +08:00 committed by Marcelo Tosatti
parent 4293b5e5a6
commit c08800a56c
1 changed files with 8 additions and 0 deletions
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8
arch/x86/kvm/vmx.c
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@ -3227,6 +3227,14 @@ 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;
}