| Message ID | 563A5D7D.4080201@wiesinger.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 04/11/2015 20:33, Gerhard Wiesinger wrote: > Signed-off-by: Gerhard Wiesinger <lists@wiesinger.com> > --- > arch/x86/kvm/svm.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > index 2f9ed1f..e0b00fc 100644 > --- a/arch/x86/kvm/svm.c > +++ b/arch/x86/kvm/svm.c > @@ -198,6 +198,10 @@ static bool npt_enabled; > static int npt = true; > module_param(npt, int, S_IRUGO); > +/* allow backward compatibility with e.g. old DOS application */ > +static int npt_task_switch_emulation = true; > +module_param(npt_task_switch_emulation, int, S_IRUGO); > + > /* allow nested virtualization in KVM/SVM */ > static int nested = true; > module_param(nested, int, S_IRUGO); > @@ -1177,6 +1181,9 @@ static void init_vmcb(struct vcpu_svm *svm, bool > init_event) > if (npt_enabled) { > /* Setup VMCB for Nested Paging */ > control->nested_ctl = 1; > + if (!npt_task_switch_emulation) { > + clr_intercept(svm, INTERCEPT_TASK_SWITCH); > + } > clr_intercept(svm, INTERCEPT_INVLPG); > clr_exception_intercept(svm, PF_VECTOR); > clr_cr_intercept(svm, INTERCEPT_CR3_READ); What is the problem you are seeing? KVM can emulate task switches; the intercept is set here because of a processor erratum that can mess them up even though, in theory, AMD supports task switching from guest mode. Paolo -- 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 04.11.2015 22:27, Paolo Bonzini wrote: > > On 04/11/2015 20:33, Gerhard Wiesinger wrote: >> Signed-off-by: Gerhard Wiesinger <lists@wiesinger.com> >> --- >> arch/x86/kvm/svm.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c >> index 2f9ed1f..e0b00fc 100644 >> --- a/arch/x86/kvm/svm.c >> +++ b/arch/x86/kvm/svm.c >> @@ -198,6 +198,10 @@ static bool npt_enabled; >> static int npt = true; >> module_param(npt, int, S_IRUGO); >> +/* allow backward compatibility with e.g. old DOS application */ >> +static int npt_task_switch_emulation = true; >> +module_param(npt_task_switch_emulation, int, S_IRUGO); >> + >> /* allow nested virtualization in KVM/SVM */ >> static int nested = true; >> module_param(nested, int, S_IRUGO); >> @@ -1177,6 +1181,9 @@ static void init_vmcb(struct vcpu_svm *svm, bool >> init_event) >> if (npt_enabled) { >> /* Setup VMCB for Nested Paging */ >> control->nested_ctl = 1; >> + if (!npt_task_switch_emulation) { >> + clr_intercept(svm, INTERCEPT_TASK_SWITCH); >> + } >> clr_intercept(svm, INTERCEPT_INVLPG); >> clr_exception_intercept(svm, PF_VECTOR); >> clr_cr_intercept(svm, INTERCEPT_CR3_READ); > What is the problem you are seeing? KVM can emulate task switches; the > intercept is set here because of a processor erratum that can mess them > up even though, in theory, AMD supports task switching from guest mode. See old thread: https://lists.nongnu.org/archive/html/qemu-devel/2012-04/msg01506.html Ciao, Gerhard -- 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 04/11/2015 22:33, Gerhard Wiesinger wrote: >>> >> What is the problem you are seeing? KVM can emulate task switches; the >> intercept is set here because of a processor erratum that can mess them >> up even though, in theory, AMD supports task switching from guest mode. > > See old thread: > https://lists.nongnu.org/archive/html/qemu-devel/2012-04/msg01506.html Can you obtain the traces you were asked for at the time? Paolo -- 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 04.11.2015 23:04, Paolo Bonzini wrote: > > On 04/11/2015 22:33, Gerhard Wiesinger wrote: >>> What is the problem you are seeing? KVM can emulate task switches; the >>> intercept is set here because of a processor erratum that can mess them >>> up even though, in theory, AMD supports task switching from guest mode. >> See old thread: >> https://lists.nongnu.org/archive/html/qemu-devel/2012-04/msg01506.html > Can you obtain the traces you were asked for at the time? ./trace-cmd record -b 20000 -e kvm ./trace-cmd report | grep -i task_switch qemu-system-x86-6024 [001] 792774.719297: kvm_exit: reason task_switch rip 0x4883 info 158 4000000000 But I can't interpret it. But I know my patch works well. Since it is just a module parameter it is fully backward compatible by default and because of the one liner no side effects are possible. So a intergration would be good. Ciao, Gerhard -- 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 05/11/2015 17:07, Gerhard Wiesinger wrote: >> > > ./trace-cmd record -b 20000 -e kvm > ./trace-cmd report | grep -i task_switch > qemu-system-x86-6024 [001] 792774.719297: kvm_exit: reason task_switch > rip 0x4883 info 158 4000000000 0x158 is the segment selector of the incoming TSS, and the task switch was caused by a far jump. > But I can't interpret it. Neither can I; you have to send the whole trace. > But I know my patch works well. Since it is > just a module parameter it is fully backward compatible by default and > because of the one liner no side effects are possible. So a intergration > would be good. It's also papering over a bug, and likely the bug still triggers on Intel systems. So it's not acceptable. Can you provide reproduction instructions please? Paolo -- 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 05/11/2015 17:15, Paolo Bonzini wrote: > > > On 05/11/2015 17:07, Gerhard Wiesinger wrote: >>> >> >> ./trace-cmd record -b 20000 -e kvm >> ./trace-cmd report | grep -i task_switch >> qemu-system-x86-6024 [001] 792774.719297: kvm_exit: reason task_switch >> rip 0x4883 info 158 4000000000 > > 0x158 is the segment selector of the incoming TSS, and the task switch > was caused by a far jump. > >> But I can't interpret it. > > Neither can I; you have to send the whole trace. > >> But I know my patch works well. Since it is >> just a module parameter it is fully backward compatible by default and >> because of the one liner no side effects are possible. So a intergration >> would be good. > > It's also papering over a bug, and likely the bug still triggers on > Intel systems. So it's not acceptable. > > Can you provide reproduction instructions please? At the very least, does it reproduce without KVM? Paolo -- 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/svm.c b/arch/x86/kvm/svm.c index 2f9ed1f..e0b00fc 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -198,6 +198,10 @@ static bool npt_enabled; static int npt = true; module_param(npt, int, S_IRUGO); +/* allow backward compatibility with e.g. old DOS application */ +static int npt_task_switch_emulation = true; +module_param(npt_task_switch_emulation, int, S_IRUGO); + /* allow nested virtualization in KVM/SVM */ static int nested = true; module_param(nested, int, S_IRUGO); @@ -1177,6 +1181,9 @@ static void init_vmcb(struct vcpu_svm *svm, bool
Signed-off-by: Gerhard Wiesinger <lists@wiesinger.com> --- arch/x86/kvm/svm.c | 7 +++++++ 1 file changed, 7 insertions(+) init_event) if (npt_enabled) { /* Setup VMCB for Nested Paging */ control->nested_ctl = 1; + if (!npt_task_switch_emulation) { + clr_intercept(svm, INTERCEPT_TASK_SWITCH); + } clr_intercept(svm, INTERCEPT_INVLPG); clr_exception_intercept(svm, PF_VECTOR); clr_cr_intercept(svm, INTERCEPT_CR3_READ);