[PATCH] KVM-USER: Fix for CPU interrupts in QEMU

[PATCH] KVM-USER: Fix for CPU interrupts in QEMU

[Gregory Haskins]

QEMU-KVM has a bug where the interruptibility of the CPU is predicated on
pending interrupts.  If the reason that a CPU is interrupted is because we
need to inject interrupts, the current code will just keep looping and miss
the event window.

This doesnt seem to cause problems with in-trunk KVM.  However, once we turn
on in-kernel HALTING, QEMU starts to have some serious problems that were
attributed to this bug.

Signed-off-by: Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org>
---

 qemu/qemu-kvm.c |    5 +----
 1 files changed, 1 insertions(+), 4 deletions(-)

diff --git a/qemu/qemu-kvm.c b/qemu/qemu-kvm.c
index 1849997..5b5c739 100644
--- a/qemu/qemu-kvm.c
+++ b/qemu/qemu-kvm.c
@@ -452,11 +452,8 @@ void kvm_save_registers(CPUState *env)
 int kvm_cpu_exec(CPUState *env)
 {
     int r;
-    int pending = (!env->ready_for_interrupt_injection ||
-                   ((env->interrupt_request & CPU_INTERRUPT_HARD) &&
-		   (env->eflags & IF_MASK)));
 
-    if (!pending && (env->interrupt_request & CPU_INTERRUPT_EXIT)) {
+    if (env->interrupt_request & CPU_INTERRUPT_EXIT) {
         env->interrupt_request &= ~CPU_INTERRUPT_EXIT;
         env->exception_index = EXCP_INTERRUPT;
         cpu_loop_exit();


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Re: [PATCH] KVM-USER: Fix for CPU interrupts in QEMU

[Dong, Eddie]

Greg:
	I think you need to do the whole patch for this including kernel
side. Will u ?
eddie

Gregory Haskins wrote:
> QEMU-KVM has a bug where the interruptibility of the CPU is
> predicated on pending interrupts.  If the reason that a CPU is
> interrupted 
> is because we
> need to inject interrupts, the current code will just keep
> looping and miss
> the event window.
> 
> This doesnt seem to cause problems with in-trunk KVM.
> However, once we turn
> on in-kernel HALTING, QEMU starts to have some serious
> problems that were
> attributed to this bug.
> 
> Signed-off-by: Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> ---
> 
> qemu/qemu-kvm.c |    5 +----
> 1 files changed, 1 insertions(+), 4 deletions(-)
> 
> diff --git a/qemu/qemu-kvm.c b/qemu/qemu-kvm.c
> index 1849997..5b5c739 100644
> --- a/qemu/qemu-kvm.c
> +++ b/qemu/qemu-kvm.c
> @@ -452,11 +452,8 @@ void kvm_save_registers(CPUState *env)
> int kvm_cpu_exec(CPUState *env)
> {
>     int r;
> -    int pending = (!env->ready_for_interrupt_injection ||
> -                   ((env->interrupt_request & CPU_INTERRUPT_HARD) &&
> -		   (env->eflags & IF_MASK)));
> 
> -    if (!pending && (env->interrupt_request & CPU_INTERRUPT_EXIT)) {
> +    if (env->interrupt_request & CPU_INTERRUPT_EXIT) {
>         env->interrupt_request &= ~CPU_INTERRUPT_EXIT;
>         env->exception_index = EXCP_INTERRUPT;
>         cpu_loop_exit();

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Re: [PATCH] KVM-USER: Fix for CPU interrupts in QEMU

[Avi Kivity]

Gregory Haskins wrote:
> QEMU-KVM has a bug where the interruptibility of the CPU is predicated on
> pending interrupts.  If the reason that a CPU is interrupted is because we
> need to inject interrupts, the current code will just keep looping and miss
> the event window.
>
> This doesnt seem to cause problems with in-trunk KVM.  However, once we turn
> on in-kernel HALTING, QEMU starts to have some serious problems that were
> attributed to this bug.
>
> Signed-off-by: Gregory Haskins <ghaskins-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org>
> ---
>
>  qemu/qemu-kvm.c |    5 +----
>  1 files changed, 1 insertions(+), 4 deletions(-)
>
> diff --git a/qemu/qemu-kvm.c b/qemu/qemu-kvm.c
> index 1849997..5b5c739 100644
> --- a/qemu/qemu-kvm.c
> +++ b/qemu/qemu-kvm.c
> @@ -452,11 +452,8 @@ void kvm_save_registers(CPUState *env)
>  int kvm_cpu_exec(CPUState *env)
>  {
>      int r;
> -    int pending = (!env->ready_for_interrupt_injection ||
> -                   ((env->interrupt_request & CPU_INTERRUPT_HARD) &&
> -		   (env->eflags & IF_MASK)));
>  
> -    if (!pending && (env->interrupt_request & CPU_INTERRUPT_EXIT)) {
> +    if (env->interrupt_request & CPU_INTERRUPT_EXIT) {
>          env->interrupt_request &= ~CPU_INTERRUPT_EXIT;
>          env->exception_index = EXCP_INTERRUPT;
>          cpu_loop_exit();
>
>   

When applied to current HEAD, this doesn't work.  Booting windows or 
Linux, quite soon during boot everything freezes.


-- 
error compiling committee.c: too many arguments to function


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Re: [PATCH] KVM-USER: Fix for CPU interrupts in QEMU

[Gregory Haskins]

On Thu, 2007-07-12 at 23:39 +0800, Dong, Eddie wrote:
> Greg:
> 	I think you need to do the whole patch for this including kernel
> side. Will u ?

Ya, I can do that.  But I probably wont be able to look at it until this
RT stuff I am working on is done.

-Greg





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Re: [PATCH] KVM-USER: Fix for CPU interrupts in QEMU

[Dong, Eddie]

Gregory Haskins wrote:
> On Thu, 2007-07-12 at 23:39 +0800, Dong, Eddie wrote:
>> Greg:
>> 	I think you need to do the whole patch for this including kernel
>> side. Will u ?
> 
> Ya, I can do that.  But I probably wont be able to look at it until
> this RT stuff I am working on is done.
> 
Then, Avi:
	Will u check that into lapic2 now, or wait for Greg back to do
more regresstion test and then check in more aggressive approach to
kvm.git? i.e. kernel hlt emulation even for user level irq.
thx,eddie

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Re: [PATCH] KVM-USER: Fix for CPU interrupts in QEMU

[Avi Kivity]

Dong, Eddie wrote:
> Gregory Haskins wrote:
>   
>> On Thu, 2007-07-12 at 23:39 +0800, Dong, Eddie wrote:
>>     
>>> Greg:
>>> 	I think you need to do the whole patch for this including kernel
>>> side. Will u ?
>>>       
>> Ya, I can do that.  But I probably wont be able to look at it until
>> this RT stuff I am working on is done.
>>
>>     
> Then, Avi:
> 	Will u check that into lapic2 now, or wait for Greg back to do
> more regresstion test and then check in more aggressive approach to
> kvm.git? i.e. kernel hlt emulation even for user level irq.
> thx,eddie
>   

I'll merge it into mainline and rebase lapic2 on top of that, on Sunday.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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Re: [PATCH] KVM-USER: Fix for CPU interrupts in QEMU

[Gregory Haskins]

On Sun, 2007-07-15 at 10:39 +0300, Avi Kivity wrote:

> When applied to current HEAD, this doesn't work.  Booting windows or 
> Linux, quite soon during boot everything freezes.


Crap.  Not sure whats happening as I definitely tested that during
development.  Ill have to take a look.

-Greg


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