From c08800a56cb8622bb61577abb4a120c6fdc4b9be Mon Sep 17 00:00:00 2001 From: Dongxiao Xu Date: Mon, 4 Feb 2013 11:50:43 +0800 Subject: [PATCH] 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 Reviewed-by: Paolo Bonzini Signed-off-by: Dongxiao Xu Signed-off-by: Xiantao Zhang Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/vmx.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 0cf74a641dec..fe9a9cfadbd6 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -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; }