From: Wanpeng Li <[email protected]>
------------[ cut here ]------------
WARNING: CPU: 5 PID: 2288 at arch/x86/kvm/vmx.c:11124 nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
CPU: 5 PID: 2288 Comm: qemu-system-x86 Not tainted 4.13.0-rc2+ #7
RIP: 0010:nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
Call Trace:
vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
? vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
kvm_arch_vcpu_ioctl_run+0x5dd/0x1be0 [kvm]
? vmx_vcpu_load+0x1be/0x220 [kvm_intel]
? kvm_arch_vcpu_load+0x62/0x230 [kvm]
kvm_vcpu_ioctl+0x340/0x700 [kvm]
? kvm_vcpu_ioctl+0x340/0x700 [kvm]
? __fget+0xfc/0x210
do_vfs_ioctl+0xa4/0x6a0
? __fget+0x11d/0x210
SyS_ioctl+0x79/0x90
do_syscall_64+0x8f/0x750
? trace_hardirqs_on_thunk+0x1a/0x1c
entry_SYSCALL64_slow_path+0x25/0x25
This can be reproduced by booting L1 guest w/ 'noapic' grub parameter, which
means that tells the kernel to not make use of any IOAPICs that may be present
in the system.
Actually external_intr variable in nested_vmx_vmexit() is the req_int_win
variable passed from vcpu_enter_guest() which means that the L0's userspace
requests an irq window. I observed the scenario (!kvm_cpu_has_interrupt(vcpu) &&
L0's userspace reqeusts an irq window) is true, so there is no interrupt which
L1 requires to inject to L2, we should not attempt to emualte "Acknowledge
interrupt on exit" for the irq window requirement in this scenario.
This patch fixes it by not attempt to emulate "Acknowledge interrupt on exit"
if there is no L1 requirement to inject an interrupt to L2.
Cc: Paolo Bonzini <[email protected]>
Cc: Radim Krčmář <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
v1 -> v2:
* update patch description
* check nested_exit_intr_ack_set() first
arch/x86/kvm/vmx.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2737343..c5a0ab5 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -11118,8 +11118,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
vmx_switch_vmcs(vcpu, &vmx->vmcs01);
- if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
- && nested_exit_intr_ack_set(vcpu)) {
+ if (nested_exit_intr_ack_set(vcpu) &&
+ exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
+ kvm_cpu_has_interrupt(vcpu)) {
int irq = kvm_cpu_get_interrupt(vcpu);
WARN_ON(irq < 0);
vmcs12->vm_exit_intr_info = irq |
--
2.7.4
2017-07-31 19:25-0700, Wanpeng Li:
> From: Wanpeng Li <[email protected]>
>
> ------------[ cut here ]------------
> WARNING: CPU: 5 PID: 2288 at arch/x86/kvm/vmx.c:11124 nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
> CPU: 5 PID: 2288 Comm: qemu-system-x86 Not tainted 4.13.0-rc2+ #7
> RIP: 0010:nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
> Call Trace:
> vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
> ? vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
> kvm_arch_vcpu_ioctl_run+0x5dd/0x1be0 [kvm]
> ? vmx_vcpu_load+0x1be/0x220 [kvm_intel]
> ? kvm_arch_vcpu_load+0x62/0x230 [kvm]
> kvm_vcpu_ioctl+0x340/0x700 [kvm]
> ? kvm_vcpu_ioctl+0x340/0x700 [kvm]
> ? __fget+0xfc/0x210
> do_vfs_ioctl+0xa4/0x6a0
> ? __fget+0x11d/0x210
> SyS_ioctl+0x79/0x90
> do_syscall_64+0x8f/0x750
> ? trace_hardirqs_on_thunk+0x1a/0x1c
> entry_SYSCALL64_slow_path+0x25/0x25
>
> This can be reproduced by booting L1 guest w/ 'noapic' grub parameter, which
> means that tells the kernel to not make use of any IOAPICs that may be present
> in the system.
>
> Actually external_intr variable in nested_vmx_vmexit() is the req_int_win
> variable passed from vcpu_enter_guest() which means that the L0's userspace
> requests an irq window. I observed the scenario (!kvm_cpu_has_interrupt(vcpu) &&
> L0's userspace reqeusts an irq window) is true, so there is no interrupt which
> L1 requires to inject to L2, we should not attempt to emualte "Acknowledge
> interrupt on exit" for the irq window requirement in this scenario.
>
> This patch fixes it by not attempt to emulate "Acknowledge interrupt on exit"
> if there is no L1 requirement to inject an interrupt to L2.
>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> v1 -> v2:
> * update patch description
> * check nested_exit_intr_ack_set() first
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> @@ -11118,8 +11118,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>
> vmx_switch_vmcs(vcpu, &vmx->vmcs01);
>
> - if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
> - && nested_exit_intr_ack_set(vcpu)) {
> + if (nested_exit_intr_ack_set(vcpu) &&
> + exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
> + kvm_cpu_has_interrupt(vcpu)) {
This would work as a solution, but I don't think it's the correct
behavior.
SDM says that with acknowledge interrupt on exit, bit 31 of the VM-exit
interrupt information (valid interrupt) is always set to 1 on
EXIT_REASON_EXTERNAL_INTERRUPT. We don't want to break hypervisors
expecting an interrupt in that case, so we should do a userspace VM exit
when the window is open and then inject the userspace interrupt with a
VM exit.
The simplest thing that came to my mind is to:
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 39a6222bf968..9ad0c882c4f5 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -10687,7 +10687,8 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
return 0;
}
- if ((kvm_cpu_has_interrupt(vcpu) || external_intr) &&
+ if ((kvm_cpu_has_interrupt(vcpu) ||
+ (external_intr && !nested_exit_intr_ack_set(vcpu))) &&
nested_exit_on_intr(vcpu)) {
if (vmx->nested.nested_run_pending)
return -EBUSY;
but I think it could break more ... actually, why was the window closed?
kvm_vcpu_ready_for_interrupt_injection() checks vmx_interrupt_allowed()
in order to decide need for the window, but vmx_check_nested_events()
doesn't care about that at all, so the window might just appear closed.
Would the following hunk help too?
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 39a6222bf968..7e6caa9c225d 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -5567,8 +5567,10 @@ static int vmx_nmi_allowed(struct kvm_vcpu *vcpu)
static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu)
{
- return (!to_vmx(vcpu)->nested.nested_run_pending &&
- vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF) &&
+ if (is_guest_mode(vcpu))
+ return !to_vmx(vcpu)->nested.nested_run_pending;
+
+ return vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF &&
!(vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) &
(GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS));
}
(It doesn't prevent malicious userspace from hitting the WARN, though.)
Thanks.
2017-08-02 3:59 GMT+08:00 Radim Krčmář <[email protected]>:
> 2017-07-31 19:25-0700, Wanpeng Li:
>> From: Wanpeng Li <[email protected]>
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 5 PID: 2288 at arch/x86/kvm/vmx.c:11124 nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
>> CPU: 5 PID: 2288 Comm: qemu-system-x86 Not tainted 4.13.0-rc2+ #7
>> RIP: 0010:nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
>> Call Trace:
>> vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
>> ? vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
>> kvm_arch_vcpu_ioctl_run+0x5dd/0x1be0 [kvm]
>> ? vmx_vcpu_load+0x1be/0x220 [kvm_intel]
>> ? kvm_arch_vcpu_load+0x62/0x230 [kvm]
>> kvm_vcpu_ioctl+0x340/0x700 [kvm]
>> ? kvm_vcpu_ioctl+0x340/0x700 [kvm]
>> ? __fget+0xfc/0x210
>> do_vfs_ioctl+0xa4/0x6a0
>> ? __fget+0x11d/0x210
>> SyS_ioctl+0x79/0x90
>> do_syscall_64+0x8f/0x750
>> ? trace_hardirqs_on_thunk+0x1a/0x1c
>> entry_SYSCALL64_slow_path+0x25/0x25
>>
>> This can be reproduced by booting L1 guest w/ 'noapic' grub parameter, which
>> means that tells the kernel to not make use of any IOAPICs that may be present
>> in the system.
>>
>> Actually external_intr variable in nested_vmx_vmexit() is the req_int_win
>> variable passed from vcpu_enter_guest() which means that the L0's userspace
>> requests an irq window. I observed the scenario (!kvm_cpu_has_interrupt(vcpu) &&
>> L0's userspace reqeusts an irq window) is true, so there is no interrupt which
>> L1 requires to inject to L2, we should not attempt to emualte "Acknowledge
>> interrupt on exit" for the irq window requirement in this scenario.
>>
>> This patch fixes it by not attempt to emulate "Acknowledge interrupt on exit"
>> if there is no L1 requirement to inject an interrupt to L2.
>>
>> Cc: Paolo Bonzini <[email protected]>
>> Cc: Radim Krčmář <[email protected]>
>> Signed-off-by: Wanpeng Li <[email protected]>
>> ---
>> v1 -> v2:
>> * update patch description
>> * check nested_exit_intr_ack_set() first
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> @@ -11118,8 +11118,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>>
>> vmx_switch_vmcs(vcpu, &vmx->vmcs01);
>>
>> - if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
>> - && nested_exit_intr_ack_set(vcpu)) {
>> + if (nested_exit_intr_ack_set(vcpu) &&
>> + exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
>> + kvm_cpu_has_interrupt(vcpu)) {
>
> This would work as a solution, but I don't think it's the correct
> behavior.
>
> SDM says that with acknowledge interrupt on exit, bit 31 of the VM-exit
> interrupt information (valid interrupt) is always set to 1 on
> EXIT_REASON_EXTERNAL_INTERRUPT. We don't want to break hypervisors
> expecting an interrupt in that case, so we should do a userspace VM exit
> when the window is open and then inject the userspace interrupt with a
> VM exit.
Agreed.
>
> The simplest thing that came to my mind is to:
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 39a6222bf968..9ad0c882c4f5 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -10687,7 +10687,8 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
> return 0;
> }
>
> - if ((kvm_cpu_has_interrupt(vcpu) || external_intr) &&
> + if ((kvm_cpu_has_interrupt(vcpu) ||
> + (external_intr && !nested_exit_intr_ack_set(vcpu))) &&
> nested_exit_on_intr(vcpu)) {
> if (vmx->nested.nested_run_pending)
> return -EBUSY;
>
Agreed.
> but I think it could break more ... actually, why was the window closed?
>
> kvm_vcpu_ready_for_interrupt_injection() checks vmx_interrupt_allowed()
> in order to decide need for the window, but vmx_check_nested_events()
> doesn't care about that at all, so the window might just appear closed.
> Would the following hunk help too?
In addition, the request window can be requested by L0's userspace
(kvm_arch_pre_run), and the idea below still can't fix in my testing.
Regards,
Wanpeng Li
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 39a6222bf968..7e6caa9c225d 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5567,8 +5567,10 @@ static int vmx_nmi_allowed(struct kvm_vcpu *vcpu)
>
> static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu)
> {
> - return (!to_vmx(vcpu)->nested.nested_run_pending &&
> - vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF) &&
> + if (is_guest_mode(vcpu))
> + return !to_vmx(vcpu)->nested.nested_run_pending;
> +
> + return vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF &&
> !(vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) &
> (GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS));
> }
>
> (It doesn't prevent malicious userspace from hitting the WARN, though.)
>
> Thanks.
2017-08-02 6:42 GMT+08:00 Wanpeng Li <[email protected]>:
> 2017-08-02 3:59 GMT+08:00 Radim Krčmář <[email protected]>:
>> 2017-07-31 19:25-0700, Wanpeng Li:
>>> From: Wanpeng Li <[email protected]>
>>>
>>> ------------[ cut here ]------------
>>> WARNING: CPU: 5 PID: 2288 at arch/x86/kvm/vmx.c:11124 nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
>>> CPU: 5 PID: 2288 Comm: qemu-system-x86 Not tainted 4.13.0-rc2+ #7
>>> RIP: 0010:nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
>>> Call Trace:
>>> vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
>>> ? vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
>>> kvm_arch_vcpu_ioctl_run+0x5dd/0x1be0 [kvm]
>>> ? vmx_vcpu_load+0x1be/0x220 [kvm_intel]
>>> ? kvm_arch_vcpu_load+0x62/0x230 [kvm]
>>> kvm_vcpu_ioctl+0x340/0x700 [kvm]
>>> ? kvm_vcpu_ioctl+0x340/0x700 [kvm]
>>> ? __fget+0xfc/0x210
>>> do_vfs_ioctl+0xa4/0x6a0
>>> ? __fget+0x11d/0x210
>>> SyS_ioctl+0x79/0x90
>>> do_syscall_64+0x8f/0x750
>>> ? trace_hardirqs_on_thunk+0x1a/0x1c
>>> entry_SYSCALL64_slow_path+0x25/0x25
>>>
>>> This can be reproduced by booting L1 guest w/ 'noapic' grub parameter, which
>>> means that tells the kernel to not make use of any IOAPICs that may be present
>>> in the system.
>>>
>>> Actually external_intr variable in nested_vmx_vmexit() is the req_int_win
>>> variable passed from vcpu_enter_guest() which means that the L0's userspace
>>> requests an irq window. I observed the scenario (!kvm_cpu_has_interrupt(vcpu) &&
>>> L0's userspace reqeusts an irq window) is true, so there is no interrupt which
>>> L1 requires to inject to L2, we should not attempt to emualte "Acknowledge
>>> interrupt on exit" for the irq window requirement in this scenario.
>>>
>>> This patch fixes it by not attempt to emulate "Acknowledge interrupt on exit"
>>> if there is no L1 requirement to inject an interrupt to L2.
>>>
>>> Cc: Paolo Bonzini <[email protected]>
>>> Cc: Radim Krčmář <[email protected]>
>>> Signed-off-by: Wanpeng Li <[email protected]>
>>> ---
>>> v1 -> v2:
>>> * update patch description
>>> * check nested_exit_intr_ack_set() first
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> @@ -11118,8 +11118,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>>>
>>> vmx_switch_vmcs(vcpu, &vmx->vmcs01);
>>>
>>> - if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
>>> - && nested_exit_intr_ack_set(vcpu)) {
>>> + if (nested_exit_intr_ack_set(vcpu) &&
>>> + exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
>>> + kvm_cpu_has_interrupt(vcpu)) {
>>
>> This would work as a solution, but I don't think it's the correct
>> behavior.
>>
>> SDM says that with acknowledge interrupt on exit, bit 31 of the VM-exit
>> interrupt information (valid interrupt) is always set to 1 on
>> EXIT_REASON_EXTERNAL_INTERRUPT. We don't want to break hypervisors
>> expecting an interrupt in that case, so we should do a userspace VM exit
>> when the window is open and then inject the userspace interrupt with a
>> VM exit.
>
> Agreed.
>
>>
>> The simplest thing that came to my mind is to:
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 39a6222bf968..9ad0c882c4f5 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -10687,7 +10687,8 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
>> return 0;
>> }
>>
>> - if ((kvm_cpu_has_interrupt(vcpu) || external_intr) &&
>> + if ((kvm_cpu_has_interrupt(vcpu) ||
>> + (external_intr && !nested_exit_intr_ack_set(vcpu))) &&
>> nested_exit_on_intr(vcpu)) {
>> if (vmx->nested.nested_run_pending)
>> return -EBUSY;
>>
>
> Agreed.
What's your opinion, Paolo? :) Actually I considered the above idea
before, it is what SDM defined.
Regards,
Wanpeng Li
>
>> but I think it could break more ... actually, why was the window closed?
>>
>> kvm_vcpu_ready_for_interrupt_injection() checks vmx_interrupt_allowed()
>> in order to decide need for the window, but vmx_check_nested_events()
>> doesn't care about that at all, so the window might just appear closed.
>> Would the following hunk help too?
>
> In addition, the request window can be requested by L0's userspace
> (kvm_arch_pre_run), and the idea below still can't fix in my testing.
>
> Regards,
> Wanpeng Li
>
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 39a6222bf968..7e6caa9c225d 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -5567,8 +5567,10 @@ static int vmx_nmi_allowed(struct kvm_vcpu *vcpu)
>>
>> static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu)
>> {
>> - return (!to_vmx(vcpu)->nested.nested_run_pending &&
>> - vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF) &&
>> + if (is_guest_mode(vcpu))
>> + return !to_vmx(vcpu)->nested.nested_run_pending;
>> +
>> + return vmcs_readl(GUEST_RFLAGS) & X86_EFLAGS_IF &&
>> !(vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) &
>> (GUEST_INTR_STATE_STI | GUEST_INTR_STATE_MOV_SS));
>> }
>>
>> (It doesn't prevent malicious userspace from hitting the WARN, though.)
>>
>> Thanks.
On 02/08/2017 10:05, Wanpeng Li wrote:
>>>
>>> SDM says that with acknowledge interrupt on exit, bit 31 of the VM-exit
>>> interrupt information (valid interrupt) is always set to 1 on
>>> EXIT_REASON_EXTERNAL_INTERRUPT. We don't want to break hypervisors
>>> expecting an interrupt in that case, so we should do a userspace VM exit
>>> when the window is open and then inject the userspace interrupt with a
>>> VM exit.
>> Agreed.
>>
>>> The simplest thing that came to my mind is to:
>>>
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index 39a6222bf968..9ad0c882c4f5 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -10687,7 +10687,8 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr)
>>> return 0;
>>> }
>>>
>>> - if ((kvm_cpu_has_interrupt(vcpu) || external_intr) &&
>>> + if ((kvm_cpu_has_interrupt(vcpu) ||
>>> + (external_intr && !nested_exit_intr_ack_set(vcpu))) &&
>>> nested_exit_on_intr(vcpu)) {
>>> if (vmx->nested.nested_run_pending)
>>> return -EBUSY;
>>>
>> Agreed.
>
> What's your opinion, Paolo? :) Actually I considered the above idea
> before, it is what SDM defined.
Radim and I always agree. :)
Paolo
2017-07-31 19:25-0700, Wanpeng Li:
> From: Wanpeng Li <[email protected]>
>
> ------------[ cut here ]------------
> WARNING: CPU: 5 PID: 2288 at arch/x86/kvm/vmx.c:11124 nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
> CPU: 5 PID: 2288 Comm: qemu-system-x86 Not tainted 4.13.0-rc2+ #7
> RIP: 0010:nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
> Call Trace:
> vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
> ? vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
> kvm_arch_vcpu_ioctl_run+0x5dd/0x1be0 [kvm]
> ? vmx_vcpu_load+0x1be/0x220 [kvm_intel]
> ? kvm_arch_vcpu_load+0x62/0x230 [kvm]
> kvm_vcpu_ioctl+0x340/0x700 [kvm]
> ? kvm_vcpu_ioctl+0x340/0x700 [kvm]
> ? __fget+0xfc/0x210
> do_vfs_ioctl+0xa4/0x6a0
> ? __fget+0x11d/0x210
> SyS_ioctl+0x79/0x90
> do_syscall_64+0x8f/0x750
> ? trace_hardirqs_on_thunk+0x1a/0x1c
> entry_SYSCALL64_slow_path+0x25/0x25
>
> This can be reproduced by booting L1 guest w/ 'noapic' grub parameter, which
> means that tells the kernel to not make use of any IOAPICs that may be present
> in the system.
>
> Actually external_intr variable in nested_vmx_vmexit() is the req_int_win
> variable passed from vcpu_enter_guest() which means that the L0's userspace
> requests an irq window. I observed the scenario (!kvm_cpu_has_interrupt(vcpu) &&
> L0's userspace reqeusts an irq window) is true, so there is no interrupt which
> L1 requires to inject to L2, we should not attempt to emualte "Acknowledge
> interrupt on exit" for the irq window requirement in this scenario.
>
> This patch fixes it by not attempt to emulate "Acknowledge interrupt on exit"
> if there is no L1 requirement to inject an interrupt to L2.
>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> v1 -> v2:
> * update patch description
> * check nested_exit_intr_ack_set() first
>
> arch/x86/kvm/vmx.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 2737343..c5a0ab5 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -11118,8 +11118,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>
> vmx_switch_vmcs(vcpu, &vmx->vmcs01);
>
> - if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
> - && nested_exit_intr_ack_set(vcpu)) {
I've added a TODO comment so it's clearer that we should not be here if
there is no interrupt.
> + if (nested_exit_intr_ack_set(vcpu) &&
> + exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
> + kvm_cpu_has_interrupt(vcpu)) {
> int irq = kvm_cpu_get_interrupt(vcpu);
> WARN_ON(irq < 0);
> vmcs12->vm_exit_intr_info = irq |
Changed the indentation to the original alignment.
Please don't use 1 tab -- the condition and body meld, which makes it
harder to read. (2 tabs would be ok too.)
And the subject was way too long, so I changed it to
KVM: nVMX: Fix interrupt window request with "Acknowledge interrupt on exit"
Applied as it results in better behavior, even if it still is incorrect,
thanks.
2017-08-03 21:46 GMT+08:00 Radim Krčmář <[email protected]>:
> 2017-07-31 19:25-0700, Wanpeng Li:
>> From: Wanpeng Li <[email protected]>
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 5 PID: 2288 at arch/x86/kvm/vmx.c:11124 nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
>> CPU: 5 PID: 2288 Comm: qemu-system-x86 Not tainted 4.13.0-rc2+ #7
>> RIP: 0010:nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
>> Call Trace:
>> vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
>> ? vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
>> kvm_arch_vcpu_ioctl_run+0x5dd/0x1be0 [kvm]
>> ? vmx_vcpu_load+0x1be/0x220 [kvm_intel]
>> ? kvm_arch_vcpu_load+0x62/0x230 [kvm]
>> kvm_vcpu_ioctl+0x340/0x700 [kvm]
>> ? kvm_vcpu_ioctl+0x340/0x700 [kvm]
>> ? __fget+0xfc/0x210
>> do_vfs_ioctl+0xa4/0x6a0
>> ? __fget+0x11d/0x210
>> SyS_ioctl+0x79/0x90
>> do_syscall_64+0x8f/0x750
>> ? trace_hardirqs_on_thunk+0x1a/0x1c
>> entry_SYSCALL64_slow_path+0x25/0x25
>>
>> This can be reproduced by booting L1 guest w/ 'noapic' grub parameter, which
>> means that tells the kernel to not make use of any IOAPICs that may be present
>> in the system.
>>
>> Actually external_intr variable in nested_vmx_vmexit() is the req_int_win
>> variable passed from vcpu_enter_guest() which means that the L0's userspace
>> requests an irq window. I observed the scenario (!kvm_cpu_has_interrupt(vcpu) &&
>> L0's userspace reqeusts an irq window) is true, so there is no interrupt which
>> L1 requires to inject to L2, we should not attempt to emualte "Acknowledge
>> interrupt on exit" for the irq window requirement in this scenario.
>>
>> This patch fixes it by not attempt to emulate "Acknowledge interrupt on exit"
>> if there is no L1 requirement to inject an interrupt to L2.
>>
>> Cc: Paolo Bonzini <[email protected]>
>> Cc: Radim Krčmář <[email protected]>
>> Signed-off-by: Wanpeng Li <[email protected]>
>> ---
>> v1 -> v2:
>> * update patch description
>> * check nested_exit_intr_ack_set() first
>>
>> arch/x86/kvm/vmx.c | 5 +++--
>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 2737343..c5a0ab5 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -11118,8 +11118,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>>
>> vmx_switch_vmcs(vcpu, &vmx->vmcs01);
>>
>> - if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
>> - && nested_exit_intr_ack_set(vcpu)) {
>
> I've added a TODO comment so it's clearer that we should not be here if
> there is no interrupt.
>
>> + if (nested_exit_intr_ack_set(vcpu) &&
>> + exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
>> + kvm_cpu_has_interrupt(vcpu)) {
>> int irq = kvm_cpu_get_interrupt(vcpu);
>> WARN_ON(irq < 0);
>> vmcs12->vm_exit_intr_info = irq |
>
> Changed the indentation to the original alignment.
> Please don't use 1 tab -- the condition and body meld, which makes it
> harder to read. (2 tabs would be ok too.)
>
> And the subject was way too long, so I changed it to
> KVM: nVMX: Fix interrupt window request with "Acknowledge interrupt on exit"
>
> Applied as it results in better behavior, even if it still is incorrect,
> thanks.
Thanks Radim. :) In addition, I will think more about it and figure
out a finial solution.
Regards,
Wanpeng Li
On Thu, Aug 3, 2017 at 6:23 PM Wanpeng Li <[email protected]> wrote:
> Thanks Radim. :) In addition, I will think more about it and figure
> out a finial solution.
Have you had any thoughts on a final solution? We're seeing incorrect
behavior with an L1 hypervisor running under qemu with "-machine
q35,kernel-irqchip=split", and I believe this may be the cause.
In particular, VMCS12 has ACK_INTERRUPT_ON_EXIT set, but L1 is seeing
an L2 exit for "external interrupt" with the VMCS12 VM-exit
interruption information cleared to 0.