| Message ID | 1359707407-12981-1-git-send-email-dongxiao.xu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Il 01/02/2013 09:30, Dongxiao Xu ha scritto: > 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. > > 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@intel.com> > Signed-off-by: Xiantao Zhang <xiantao.zhang@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..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; > } > Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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@intel.com> > Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com> Reviewed-by: Gleb Natapov <gleb@redhat.com> 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. > > --- > 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
> -----Original Message----- > From: Gleb Natapov [mailto:gleb@redhat.com] > Sent: Sunday, February 03, 2013 9:57 PM > To: Xu, Dongxiao > Cc: kvm@vger.kernel.org > 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@intel.com> > > Signed-off-by: Xiantao Zhang <xiantao.zhang@intel.com> > Reviewed-by: Gleb Natapov <gleb@redhat.com> > > 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; }