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Groups > linux.kernel > #1684827 > unrolled thread
| Started by | Wanpeng Li <kernellwp@gmail.com> |
|---|---|
| First post | 2017-07-11 09:20 +0200 |
| Last post | 2017-07-12 16:00 +0200 |
| Articles | 4 — 3 participants |
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[PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation Wanpeng Li <kernellwp@gmail.com> - 2017-07-11 09:20 +0200
Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation Radim Krčmář <rkrcmar@redhat.com> - 2017-07-11 18:00 +0200
Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation Paolo Bonzini <pbonzini@redhat.com> - 2017-07-11 18:10 +0200
Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation Wanpeng Li <kernellwp@gmail.com> - 2017-07-12 16:00 +0200
| From | Wanpeng Li <kernellwp@gmail.com> |
|---|---|
| Date | 2017-07-11 09:20 +0200 |
| Subject | [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation |
| Message-ID | <u1XCF-7G3-5@gated-at.bofh.it> |
From: Wanpeng Li <wanpeng.li@hotmail.com> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries to emulate invalid guest state task-switch: kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 kvm_emulate_insn: 42000:0:0f 0b (0x2) kvm_emulate_insn: 42000:0:0f 0b (0x2) failed kvm_inj_exception: #UD (0x0) kvm_entry: vcpu 0 kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 kvm_emulate_insn: 42000:0:0f 0b (0x2) kvm_emulate_insn: 42000:0:0f 0b (0x2) failed kvm_inj_exception: #UD (0x0) ...................... It appears that the task-switch emulation updates rflags (and vm86 flag) only after the segments are loaded, causing vmx->emulation_required to be set, when in fact invalid guest state emulation is not needed. This patch fixes it by updating vmx->emulation_required after the rflags (and vm86 flag) is updated in task-switch emulation. Suggested-by: Nadav Amit <nadav.amit@gmail.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> --- arch/x86/kvm/vmx.c | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index f50cbfd..70270a2 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6255,6 +6255,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu) * TODO: What about debug traps on tss switch? * Are we supposed to inject them and update dr6? */ + vmx->emulation_required = emulation_required(vcpu); return 1; } -- 2.7.4
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| From | Radim Krčmář <rkrcmar@redhat.com> |
|---|---|
| Date | 2017-07-11 18:00 +0200 |
| Subject | Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation |
| Message-ID | <u25JU-4bX-19@gated-at.bofh.it> |
| In reply to | #1684827 |
2017-07-11 00:13-0700, Wanpeng Li: > From: Wanpeng Li <wanpeng.li@hotmail.com> > > This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y > or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries > to emulate invalid guest state task-switch: > > kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 > kvm_emulate_insn: 42000:0:0f 0b (0x2) > kvm_emulate_insn: 42000:0:0f 0b (0x2) failed > kvm_inj_exception: #UD (0x0) > kvm_entry: vcpu 0 > kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 > kvm_emulate_insn: 42000:0:0f 0b (0x2) > kvm_emulate_insn: 42000:0:0f 0b (0x2) failed > kvm_inj_exception: #UD (0x0) > ...................... > > It appears that the task-switch emulation updates rflags (and vm86 > flag) only after the segments are loaded, causing vmx->emulation_required > to be set, when in fact invalid guest state emulation is not needed. > > This patch fixes it by updating vmx->emulation_required after the > rflags (and vm86 flag) is updated in task-switch emulation. > > Suggested-by: Nadav Amit <nadav.amit@gmail.com> > Cc: Paolo Bonzini <pbonzini@redhat.com> > Cc: Radim Krčmář <rkrcmar@redhat.com> > Cc: Nadav Amit <nadav.amit@gmail.com> > Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> > --- > arch/x86/kvm/vmx.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index f50cbfd..70270a2 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -6255,6 +6255,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu) > * TODO: What about debug traps on tss switch? > * Are we supposed to inject them and update dr6? > */ > + vmx->emulation_required = emulation_required(vcpu); Hm, so the problem happened because changes to rflags can flip the value of emulation_required(). I would add this line to vmx_set_rflags() to make sure that we fixed everything, thanks.
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| From | Paolo Bonzini <pbonzini@redhat.com> |
|---|---|
| Date | 2017-07-11 18:10 +0200 |
| Subject | Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation |
| Message-ID | <u25Tz-4wz-1@gated-at.bofh.it> |
| In reply to | #1685172 |
On 11/07/2017 17:54, Radim Krčmář wrote: > 2017-07-11 00:13-0700, Wanpeng Li: >> From: Wanpeng Li <wanpeng.li@hotmail.com> >> >> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y >> or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries >> to emulate invalid guest state task-switch: >> >> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 >> kvm_emulate_insn: 42000:0:0f 0b (0x2) >> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed >> kvm_inj_exception: #UD (0x0) >> kvm_entry: vcpu 0 >> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 >> kvm_emulate_insn: 42000:0:0f 0b (0x2) >> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed >> kvm_inj_exception: #UD (0x0) >> ...................... >> >> It appears that the task-switch emulation updates rflags (and vm86 >> flag) only after the segments are loaded, causing vmx->emulation_required >> to be set, when in fact invalid guest state emulation is not needed. >> >> This patch fixes it by updating vmx->emulation_required after the >> rflags (and vm86 flag) is updated in task-switch emulation. >> >> Suggested-by: Nadav Amit <nadav.amit@gmail.com> >> Cc: Paolo Bonzini <pbonzini@redhat.com> >> Cc: Radim Krčmář <rkrcmar@redhat.com> >> Cc: Nadav Amit <nadav.amit@gmail.com> >> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >> --- >> arch/x86/kvm/vmx.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index f50cbfd..70270a2 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -6255,6 +6255,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu) >> * TODO: What about debug traps on tss switch? >> * Are we supposed to inject them and update dr6? >> */ >> + vmx->emulation_required = emulation_required(vcpu); > > Hm, so the problem happened because changes to rflags can flip the value > of emulation_required(). I would add this line to vmx_set_rflags() to > make sure that we fixed everything, thanks. Note that there is some extra complication, because emulation_required is expensive and you'll want to run it only when EFLAGS.VM changes. Paolo
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| From | Wanpeng Li <kernellwp@gmail.com> |
|---|---|
| Date | 2017-07-12 16:00 +0200 |
| Subject | Re: [PATCH] KVM: VMX: Fix invalid guest state detection after task-switch emulation |
| Message-ID | <u2qlj-t8-7@gated-at.bofh.it> |
| In reply to | #1685173 |
2017-07-12 0:09 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>: > On 11/07/2017 17:54, Radim Krčmář wrote: >> 2017-07-11 00:13-0700, Wanpeng Li: >>> From: Wanpeng Li <wanpeng.li@hotmail.com> >>> >>> This can be reproduced by EPT=1, unrestricted_guest=N, emulate_invalid_state=Y >>> or EPT=0, the trace of kvm-unit-tests/taskswitch2.flat is like below, it tries >>> to emulate invalid guest state task-switch: >>> >>> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 >>> kvm_emulate_insn: 42000:0:0f 0b (0x2) >>> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed >>> kvm_inj_exception: #UD (0x0) >>> kvm_entry: vcpu 0 >>> kvm_exit: reason TASK_SWITCH rip 0x0 info 40000058 0 >>> kvm_emulate_insn: 42000:0:0f 0b (0x2) >>> kvm_emulate_insn: 42000:0:0f 0b (0x2) failed >>> kvm_inj_exception: #UD (0x0) >>> ...................... >>> >>> It appears that the task-switch emulation updates rflags (and vm86 >>> flag) only after the segments are loaded, causing vmx->emulation_required >>> to be set, when in fact invalid guest state emulation is not needed. >>> >>> This patch fixes it by updating vmx->emulation_required after the >>> rflags (and vm86 flag) is updated in task-switch emulation. >>> >>> Suggested-by: Nadav Amit <nadav.amit@gmail.com> >>> Cc: Paolo Bonzini <pbonzini@redhat.com> >>> Cc: Radim Krčmář <rkrcmar@redhat.com> >>> Cc: Nadav Amit <nadav.amit@gmail.com> >>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >>> --- >>> arch/x86/kvm/vmx.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>> index f50cbfd..70270a2 100644 >>> --- a/arch/x86/kvm/vmx.c >>> +++ b/arch/x86/kvm/vmx.c >>> @@ -6255,6 +6255,7 @@ static int handle_task_switch(struct kvm_vcpu *vcpu) >>> * TODO: What about debug traps on tss switch? >>> * Are we supposed to inject them and update dr6? >>> */ >>> + vmx->emulation_required = emulation_required(vcpu); >> >> Hm, so the problem happened because changes to rflags can flip the value >> of emulation_required(). I would add this line to vmx_set_rflags() to >> make sure that we fixed everything, thanks. > > Note that there is some extra complication, because emulation_required > is expensive and you'll want to run it only when EFLAGS.VM changes. Agreed. Regards, Wanpeng Li
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