From: Wanpeng Li <[email protected]>
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 <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Nadav Amit <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
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
2017-07-11 00:13-0700, Wanpeng Li:
> From: Wanpeng Li <[email protected]>
>
> 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 <[email protected]>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Cc: Nadav Amit <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> 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.
On 11/07/2017 17:54, Radim Krčmář wrote:
> 2017-07-11 00:13-0700, Wanpeng Li:
>> From: Wanpeng Li <[email protected]>
>>
>> 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 <[email protected]>
>> Cc: Paolo Bonzini <[email protected]>
>> Cc: Radim Krčmář <[email protected]>
>> Cc: Nadav Amit <[email protected]>
>> Signed-off-by: Wanpeng Li <[email protected]>
>> ---
>> 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
2017-07-12 0:09 GMT+08:00 Paolo Bonzini <[email protected]>:
> On 11/07/2017 17:54, Radim Krčmář wrote:
>> 2017-07-11 00:13-0700, Wanpeng Li:
>>> From: Wanpeng Li <[email protected]>
>>>
>>> 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 <[email protected]>
>>> Cc: Paolo Bonzini <[email protected]>
>>> Cc: Radim Krčmář <[email protected]>
>>> Cc: Nadav Amit <[email protected]>
>>> Signed-off-by: Wanpeng Li <[email protected]>
>>> ---
>>> 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
Ping, :)
2017-07-11 15:13 GMT+08:00 Wanpeng Li <[email protected]>:
> From: Wanpeng Li <[email protected]>
>
> 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 <[email protected]>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Cc: Nadav Amit <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> 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
>
2017-07-19 13:34+0800, Wanpeng Li:
> Ping, :)
I misunderstood where the ball is ... is the patch below ok?
---8<---
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.
Suggested-by: Nadav Amit <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
[Wanpeng wrote the commit message with initial patch and Radim moved the
update to vmx_set_rflags and added Paolo's suggestion for the check.]
Signed-off-by: Radim Krčmář <[email protected]>
---
arch/x86/kvm/vmx.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 84e62acf2dd8..a776aea0043a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
__vmx_load_host_state(to_vmx(vcpu));
}
+static bool emulation_required(struct kvm_vcpu *vcpu)
+{
+ return emulate_invalid_guest_state && !guest_state_valid(vcpu);
+}
+
static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
/*
@@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
{
+ unsigned long old_rflags = to_vmx(vcpu)->rflags;
+
__set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
to_vmx(vcpu)->rflags = rflags;
if (to_vmx(vcpu)->rmode.vm86_active) {
@@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
}
vmcs_writel(GUEST_RFLAGS, rflags);
+
+ if ((old_rflags ^ rflags) & X86_EFLAGS_VM)
+ to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
}
static u32 vmx_get_pkru(struct kvm_vcpu *vcpu)
@@ -3857,11 +3867,6 @@ static __init int alloc_kvm_area(void)
return 0;
}
-static bool emulation_required(struct kvm_vcpu *vcpu)
-{
- return emulate_invalid_guest_state && !guest_state_valid(vcpu);
-}
-
static void fix_pmode_seg(struct kvm_vcpu *vcpu, int seg,
struct kvm_segment *save)
{
--
2.13.2
Radim Krčmář <[email protected]> wrote:
> 2017-07-19 13:34+0800, Wanpeng Li:
>> Ping, :)
>
> I misunderstood where the ball is ... is the patch below ok?
>
> ---8<---
> 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.
>
> Suggested-by: Nadav Amit <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> [Wanpeng wrote the commit message with initial patch and Radim moved the
> update to vmx_set_rflags and added Paolo's suggestion for the check.]
> Signed-off-by: Radim Krčmář <[email protected]>
> ---
> arch/x86/kvm/vmx.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 84e62acf2dd8..a776aea0043a 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
> __vmx_load_host_state(to_vmx(vcpu));
> }
>
> +static bool emulation_required(struct kvm_vcpu *vcpu)
> +{
> + return emulate_invalid_guest_state && !guest_state_valid(vcpu);
> +}
> +
> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>
> /*
> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>
> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
> {
> + unsigned long old_rflags = to_vmx(vcpu)->rflags;
It assumes rflags was decached from the VMCS before. Probably it is true, but…
2017-07-19 08:14-0700, Nadav Amit:
> Radim Krčmář <[email protected]> wrote:
> > @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
> >
> > static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
> > {
> > + unsigned long old_rflags = to_vmx(vcpu)->rflags;
>
> It assumes rflags was decached from the VMCS before. Probably it is true, but…
Right, it's better to use accessors everywhere, thanks.
The line should read:
+ unsigned long old_rflags = vmx_get_rflags(vcpu);
---8<---
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.
Suggested-by: Nadav Amit <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
[Wanpeng wrote the commit message with initial patch and Radim moved the
update to vmx_set_rflags and added Paolo's suggestion for the check.]
Signed-off-by: Radim Krčmář <[email protected]>
---
arch/x86/kvm/vmx.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 84e62acf2dd8..a776aea0043a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
__vmx_load_host_state(to_vmx(vcpu));
}
+static bool emulation_required(struct kvm_vcpu *vcpu)
+{
+ return emulate_invalid_guest_state && !guest_state_valid(vcpu);
+}
+
static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
/*
@@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
{
+ unsigned long old_rflags = vmx_get_rflags(vcpu);
+
__set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
to_vmx(vcpu)->rflags = rflags;
if (to_vmx(vcpu)->rmode.vm86_active) {
@@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
}
vmcs_writel(GUEST_RFLAGS, rflags);
+
+ if ((old_rflags ^ rflags) & X86_EFLAGS_VM)
+ to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
}
static u32 vmx_get_pkru(struct kvm_vcpu *vcpu)
@@ -3857,11 +3867,6 @@ static __init int alloc_kvm_area(void)
return 0;
}
-static bool emulation_required(struct kvm_vcpu *vcpu)
-{
- return emulate_invalid_guest_state && !guest_state_valid(vcpu);
-}
-
static void fix_pmode_seg(struct kvm_vcpu *vcpu, int seg,
struct kvm_segment *save)
{
--
2.13.2
Radim Krčmář <[email protected]> wrote:
> 2017-07-19 08:14-0700, Nadav Amit:
>> Radim Krčmář <[email protected]> wrote:
>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>
>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>> {
>>> + unsigned long old_rflags = to_vmx(vcpu)->rflags;
>>
>> It assumes rflags was decached from the VMCS before. Probably it is true, but…
>
> Right, it's better to use accessors everywhere, thanks.
> The line should read:
>
> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>
> ---8<---
> 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.
>
> Suggested-by: Nadav Amit <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> [Wanpeng wrote the commit message with initial patch and Radim moved the
> update to vmx_set_rflags and added Paolo's suggestion for the check.]
> Signed-off-by: Radim Krčmář <[email protected]>
> ---
> arch/x86/kvm/vmx.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 84e62acf2dd8..a776aea0043a 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
> __vmx_load_host_state(to_vmx(vcpu));
> }
>
> +static bool emulation_required(struct kvm_vcpu *vcpu)
> +{
> + return emulate_invalid_guest_state && !guest_state_valid(vcpu);
> +}
> +
> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>
> /*
> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>
> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
> {
> + unsigned long old_rflags = vmx_get_rflags(vcpu);
> +
> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
> to_vmx(vcpu)->rflags = rflags;
> if (to_vmx(vcpu)->rmode.vm86_active) {
> @@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
> }
> vmcs_writel(GUEST_RFLAGS, rflags);
> +
> + if ((old_rflags ^ rflags) & X86_EFLAGS_VM)
> + to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
Sorry for not pointing it before, but here you compare the old_rflags with
the new rflags but after you already “massaged” it. So the value you compare
with is not what the guest “sees”.
2017-07-20 0:25 GMT+08:00 Nadav Amit <[email protected]>:
> Radim Krčmář <[email protected]> wrote:
>
>> 2017-07-19 08:14-0700, Nadav Amit:
>>> Radim Krčmář <[email protected]> wrote:
>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>>
>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>> {
>>>> + unsigned long old_rflags = to_vmx(vcpu)->rflags;
>>>
>>> It assumes rflags was decached from the VMCS before. Probably it is true, but…
>>
>> Right, it's better to use accessors everywhere, thanks.
>> The line should read:
>>
>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>
>> ---8<---
>> 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.
>>
>> Suggested-by: Nadav Amit <[email protected]>
>> Signed-off-by: Wanpeng Li <[email protected]>
>> [Wanpeng wrote the commit message with initial patch and Radim moved the
>> update to vmx_set_rflags and added Paolo's suggestion for the check.]
>> Signed-off-by: Radim Krčmář <[email protected]>
>> ---
>> arch/x86/kvm/vmx.c | 15 ++++++++++-----
>> 1 file changed, 10 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 84e62acf2dd8..a776aea0043a 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>> __vmx_load_host_state(to_vmx(vcpu));
>> }
>>
>> +static bool emulation_required(struct kvm_vcpu *vcpu)
>> +{
>> + return emulate_invalid_guest_state && !guest_state_valid(vcpu);
>> +}
>> +
>> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>>
>> /*
>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>
>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>> {
>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>> +
>> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
>> to_vmx(vcpu)->rflags = rflags;
>> if (to_vmx(vcpu)->rmode.vm86_active) {
>> @@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
>> }
>> vmcs_writel(GUEST_RFLAGS, rflags);
>> +
>> + if ((old_rflags ^ rflags) & X86_EFLAGS_VM)
>> + to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
>
> Sorry for not pointing it before, but here you compare the old_rflags with
> the new rflags but after you already “massaged” it. So the value you compare
> with is not what the guest “sees”.
So you mean we should use unsigned long old_rflags =
vmcs_readl(GUEST_RFLAGS); right?
Regards,
Wanpeng Li
Wanpeng Li <[email protected]> wrote:
> 2017-07-20 0:25 GMT+08:00 Nadav Amit <[email protected]>:
>> Radim Krčmář <[email protected]> wrote:
>>
>>> 2017-07-19 08:14-0700, Nadav Amit:
>>>> Radim Krčmář <[email protected]> wrote:
>>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>>>
>>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>>> {
>>>>> + unsigned long old_rflags = to_vmx(vcpu)->rflags;
>>>>
>>>> It assumes rflags was decached from the VMCS before. Probably it is true, but…
>>>
>>> Right, it's better to use accessors everywhere, thanks.
>>> The line should read:
>>>
>>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>>
>>> ---8<---
>>> 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.
>>>
>>> Suggested-by: Nadav Amit <[email protected]>
>>> Signed-off-by: Wanpeng Li <[email protected]>
>>> [Wanpeng wrote the commit message with initial patch and Radim moved the
>>> update to vmx_set_rflags and added Paolo's suggestion for the check.]
>>> Signed-off-by: Radim Krčmář <[email protected]>
>>> ---
>>> arch/x86/kvm/vmx.c | 15 ++++++++++-----
>>> 1 file changed, 10 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index 84e62acf2dd8..a776aea0043a 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>>> __vmx_load_host_state(to_vmx(vcpu));
>>> }
>>>
>>> +static bool emulation_required(struct kvm_vcpu *vcpu)
>>> +{
>>> + return emulate_invalid_guest_state && !guest_state_valid(vcpu);
>>> +}
>>> +
>>> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>>>
>>> /*
>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>
>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>> {
>>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>> +
>>> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
>>> to_vmx(vcpu)->rflags = rflags;
>>> if (to_vmx(vcpu)->rmode.vm86_active) {
>>> @@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
>>> }
>>> vmcs_writel(GUEST_RFLAGS, rflags);
>>> +
>>> + if ((old_rflags ^ rflags) & X86_EFLAGS_VM)
>>> + to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
>>
>> Sorry for not pointing it before, but here you compare the old_rflags with
>> the new rflags but after you already “massaged” it. So the value you compare
>> with is not what the guest “sees”.
>
> So you mean we should use unsigned long old_rflags =
> vmcs_readl(GUEST_RFLAGS); right?
No. The problem is not with old_rflags now, but with rflags. If vm86_active,
then rflags is changed and you don’t compare the guest-visible rflags
anymore.
2017-07-20 6:53 GMT+08:00 Nadav Amit <[email protected]>:
> Wanpeng Li <[email protected]> wrote:
>
>> 2017-07-20 0:25 GMT+08:00 Nadav Amit <[email protected]>:
>>> Radim Krčmář <[email protected]> wrote:
>>>
>>>> 2017-07-19 08:14-0700, Nadav Amit:
>>>>> Radim Krčmář <[email protected]> wrote:
>>>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>>>>
>>>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>>>> {
>>>>>> + unsigned long old_rflags = to_vmx(vcpu)->rflags;
>>>>>
>>>>> It assumes rflags was decached from the VMCS before. Probably it is true, but…
>>>>
>>>> Right, it's better to use accessors everywhere, thanks.
>>>> The line should read:
>>>>
>>>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>>>
>>>> ---8<---
>>>> 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.
>>>>
>>>> Suggested-by: Nadav Amit <[email protected]>
>>>> Signed-off-by: Wanpeng Li <[email protected]>
>>>> [Wanpeng wrote the commit message with initial patch and Radim moved the
>>>> update to vmx_set_rflags and added Paolo's suggestion for the check.]
>>>> Signed-off-by: Radim Krčmář <[email protected]>
>>>> ---
>>>> arch/x86/kvm/vmx.c | 15 ++++++++++-----
>>>> 1 file changed, 10 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>> index 84e62acf2dd8..a776aea0043a 100644
>>>> --- a/arch/x86/kvm/vmx.c
>>>> +++ b/arch/x86/kvm/vmx.c
>>>> @@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>>>> __vmx_load_host_state(to_vmx(vcpu));
>>>> }
>>>>
>>>> +static bool emulation_required(struct kvm_vcpu *vcpu)
>>>> +{
>>>> + return emulate_invalid_guest_state && !guest_state_valid(vcpu);
>>>> +}
>>>> +
>>>> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>>>>
>>>> /*
>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>>
>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>> {
>>>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>>> +
>>>> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
>>>> to_vmx(vcpu)->rflags = rflags;
>>>> if (to_vmx(vcpu)->rmode.vm86_active) {
>>>> @@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
>>>> }
>>>> vmcs_writel(GUEST_RFLAGS, rflags);
>>>> +
>>>> + if ((old_rflags ^ rflags) & X86_EFLAGS_VM)
>>>> + to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
>>>
>>> Sorry for not pointing it before, but here you compare the old_rflags with
>>> the new rflags but after you already “massaged” it. So the value you compare
>>> with is not what the guest “sees”.
>>
>> So you mean we should use unsigned long old_rflags =
>> vmcs_readl(GUEST_RFLAGS); right?
>
> No. The problem is not with old_rflags now, but with rflags. If vm86_active,
> then rflags is changed and you don’t compare the guest-visible rflags
> anymore.
Ah, I see. So we should compare the old_flags with the
rmode->save_rflags(guest-visible rflags) instead of the rflags (shadow
rflags), right?
Regards,
Wanpeng Li
Wanpeng Li <[email protected]> wrote:
> 2017-07-20 6:53 GMT+08:00 Nadav Amit <[email protected]>:
>> Wanpeng Li <[email protected]> wrote:
>>
>>> 2017-07-20 0:25 GMT+08:00 Nadav Amit <[email protected]>:
>>>> Radim Krčmář <[email protected]> wrote:
>>>>
>>>>> 2017-07-19 08:14-0700, Nadav Amit:
>>>>>> Radim Krčmář <[email protected]> wrote:
>>>>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>>>>>
>>>>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>>>>> {
>>>>>>> + unsigned long old_rflags = to_vmx(vcpu)->rflags;
>>>>>>
>>>>>> It assumes rflags was decached from the VMCS before. Probably it is true, but…
>>>>>
>>>>> Right, it's better to use accessors everywhere, thanks.
>>>>> The line should read:
>>>>>
>>>>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>>>>
>>>>> ---8<---
>>>>> 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.
>>>>>
>>>>> Suggested-by: Nadav Amit <[email protected]>
>>>>> Signed-off-by: Wanpeng Li <[email protected]>
>>>>> [Wanpeng wrote the commit message with initial patch and Radim moved the
>>>>> update to vmx_set_rflags and added Paolo's suggestion for the check.]
>>>>> Signed-off-by: Radim Krčmář <[email protected]>
>>>>> ---
>>>>> arch/x86/kvm/vmx.c | 15 ++++++++++-----
>>>>> 1 file changed, 10 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>>> index 84e62acf2dd8..a776aea0043a 100644
>>>>> --- a/arch/x86/kvm/vmx.c
>>>>> +++ b/arch/x86/kvm/vmx.c
>>>>> @@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>>>>> __vmx_load_host_state(to_vmx(vcpu));
>>>>> }
>>>>>
>>>>> +static bool emulation_required(struct kvm_vcpu *vcpu)
>>>>> +{
>>>>> + return emulate_invalid_guest_state && !guest_state_valid(vcpu);
>>>>> +}
>>>>> +
>>>>> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>>>>>
>>>>> /*
>>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>>>
>>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>>> {
>>>>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>>>> +
>>>>> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
>>>>> to_vmx(vcpu)->rflags = rflags;
>>>>> if (to_vmx(vcpu)->rmode.vm86_active) {
>>>>> @@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>>> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
>>>>> }
>>>>> vmcs_writel(GUEST_RFLAGS, rflags);
>>>>> +
>>>>> + if ((old_rflags ^ rflags) & X86_EFLAGS_VM)
>>>>> + to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
>>>>
>>>> Sorry for not pointing it before, but here you compare the old_rflags with
>>>> the new rflags but after you already “massaged” it. So the value you compare
>>>> with is not what the guest “sees”.
>>>
>>> So you mean we should use unsigned long old_rflags =
>>> vmcs_readl(GUEST_RFLAGS); right?
>>
>> No. The problem is not with old_rflags now, but with rflags. If vm86_active,
>> then rflags is changed and you don’t compare the guest-visible rflags
>> anymore.
>
> Ah, I see. So we should compare the old_flags with the
> rmode->save_rflags(guest-visible rflags) instead of the rflags (shadow
> rflags), right?
Not exactly, since rmode->save_rflags are invalid if !vm86_active. Instead,
I think you should have a save_rflags variable on the stack that would hold
the rflags before “massaging” and use it instead.
2017-07-20 7:06 GMT+08:00 Nadav Amit <[email protected]>:
> Wanpeng Li <[email protected]> wrote:
>
>> 2017-07-20 6:53 GMT+08:00 Nadav Amit <[email protected]>:
>>> Wanpeng Li <[email protected]> wrote:
>>>
>>>> 2017-07-20 0:25 GMT+08:00 Nadav Amit <[email protected]>:
>>>>> Radim Krčmář <[email protected]> wrote:
>>>>>
>>>>>> 2017-07-19 08:14-0700, Nadav Amit:
>>>>>>> Radim Krčmář <[email protected]> wrote:
>>>>>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>>>>>>
>>>>>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>>>>>> {
>>>>>>>> + unsigned long old_rflags = to_vmx(vcpu)->rflags;
>>>>>>>
>>>>>>> It assumes rflags was decached from the VMCS before. Probably it is true, but…
>>>>>>
>>>>>> Right, it's better to use accessors everywhere, thanks.
>>>>>> The line should read:
>>>>>>
>>>>>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>>>>>
>>>>>> ---8<---
>>>>>> 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.
>>>>>>
>>>>>> Suggested-by: Nadav Amit <[email protected]>
>>>>>> Signed-off-by: Wanpeng Li <[email protected]>
>>>>>> [Wanpeng wrote the commit message with initial patch and Radim moved the
>>>>>> update to vmx_set_rflags and added Paolo's suggestion for the check.]
>>>>>> Signed-off-by: Radim Krčmář <[email protected]>
>>>>>> ---
>>>>>> arch/x86/kvm/vmx.c | 15 ++++++++++-----
>>>>>> 1 file changed, 10 insertions(+), 5 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>>>> index 84e62acf2dd8..a776aea0043a 100644
>>>>>> --- a/arch/x86/kvm/vmx.c
>>>>>> +++ b/arch/x86/kvm/vmx.c
>>>>>> @@ -2326,6 +2326,11 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
>>>>>> __vmx_load_host_state(to_vmx(vcpu));
>>>>>> }
>>>>>>
>>>>>> +static bool emulation_required(struct kvm_vcpu *vcpu)
>>>>>> +{
>>>>>> + return emulate_invalid_guest_state && !guest_state_valid(vcpu);
>>>>>> +}
>>>>>> +
>>>>>> static void vmx_decache_cr0_guest_bits(struct kvm_vcpu *vcpu);
>>>>>>
>>>>>> /*
>>>>>> @@ -2363,6 +2368,8 @@ static unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
>>>>>>
>>>>>> static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>>>> {
>>>>>> + unsigned long old_rflags = vmx_get_rflags(vcpu);
>>>>>> +
>>>>>> __set_bit(VCPU_EXREG_RFLAGS, (ulong *)&vcpu->arch.regs_avail);
>>>>>> to_vmx(vcpu)->rflags = rflags;
>>>>>> if (to_vmx(vcpu)->rmode.vm86_active) {
>>>>>> @@ -2370,6 +2377,9 @@ static void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
>>>>>> rflags |= X86_EFLAGS_IOPL | X86_EFLAGS_VM;
>>>>>> }
>>>>>> vmcs_writel(GUEST_RFLAGS, rflags);
>>>>>> +
>>>>>> + if ((old_rflags ^ rflags) & X86_EFLAGS_VM)
>>>>>> + to_vmx(vcpu)->emulation_required = emulation_required(vcpu);
>>>>>
>>>>> Sorry for not pointing it before, but here you compare the old_rflags with
>>>>> the new rflags but after you already “massaged” it. So the value you compare
>>>>> with is not what the guest “sees”.
>>>>
>>>> So you mean we should use unsigned long old_rflags =
>>>> vmcs_readl(GUEST_RFLAGS); right?
>>>
>>> No. The problem is not with old_rflags now, but with rflags. If vm86_active,
>>> then rflags is changed and you don’t compare the guest-visible rflags
>>> anymore.
>>
>> Ah, I see. So we should compare the old_flags with the
>> rmode->save_rflags(guest-visible rflags) instead of the rflags (shadow
>> rflags), right?
>
> Not exactly, since rmode->save_rflags are invalid if !vm86_active. Instead,
> I think you should have a save_rflags variable on the stack that would hold
> the rflags before “massaging” and use it instead.
Thanks for pointing out :) I will send out a new version, in addition,
thanks Radim's help for these two versions. :)
Regards,
Wanpeng Li