> -----Original Message----- > From: Gleb Natapov [mailto:gleb@xxxxxxxxxx] > Sent: Sunday, February 03, 2013 9:57 PM > To: Xu, Dongxiao > Cc: kvm@xxxxxxxxxxxxxxx > Subject: Re: KVM: VMX: disable SMEP feature when guest is in non-paging > mode > > On Fri, Feb 01, 2013 at 08:30:07AM -0000, Xu wrote: > > 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 HAP. > Not always, only if unrestricted mode is disabled, since vm86 mode, that > is used otherwise, requires paging. > > > 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.xu@xxxxxxxxx> > > Signed-off-by: Xiantao Zhang <xiantao.zhang@xxxxxxxxx> > Reviewed-by: Gleb Natapov <gleb@xxxxxxxxxx> > > But HAP is XEN terminology AFAIK. KVM speak is tdp (two dimensional > paging). If would be nice to change it in the commit message and the > comment before committing. Thanks for reminding this. I've sent out the v2 patch to address this issue. Thanks, Dongxiao > > > > > --- > > 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..e82f20d 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 HAP. > > + * 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; > > } > > -- > Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
