[Qemu-devel] [PATCH v1 for-2.12] s390x/kvm: call cpu_synchronize_state() on every kvm_arch_handle_exit()

[Qemu-devel] [PATCH v1 for-2.12] s390x/kvm: call cpu_synchronize_state() on every kvm_arch_handle_exit()

[David Hildenbrand]

Manually having to use cpu_synchronize_state() is error prone. And as
Christian Borntraeger discovered, e.g. handle_diag() is currently
missing a cpu_synchronize_state(), as decode_basedisp_s() uses a
general purpose register value internally.

So let's do an overall cpu_synchronize_state(), which fixes at least the
one mentioned BUG. We will clean up the superfluous cpu_synchronize_state()
calls later.

We now also call it (although maybe not neded) for
- KVM_EXIT_S390_RESET -> s390_reipl_request()
- KVM_EXIT_DEBUG -> kvm_arch_handle_debug_exit()
- unmanagable/unimplemented intercepts
- ICPT_CPU_STOP -> do_stop_interrupt() -> cpu gets halted
- Scenarios where we inject an operation exception
- handle_stsi()

I don't think any of these are performance critical. Especially as we
have all information directly contained in kvm_run, there are no
additional IOCTLs to issue on modern kernels.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 target/s390x/kvm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
index f570896dc1..fb59d92def 100644
--- a/target/s390x/kvm.c
+++ b/target/s390x/kvm.c
@@ -1778,6 +1778,8 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
 
     qemu_mutex_lock_iothread();
 
+    cpu_synchronize_state(cs);
+
     switch (run->exit_reason) {
         case KVM_EXIT_S390_SIEIC:
             ret = handle_intercept(cpu);
-- 
2.14.3

Re: [Qemu-devel] [PATCH v1 for-2.12] s390x/kvm: call cpu_synchronize_state() on every kvm_arch_handle_exit()

[Thomas Huth]

On 06.04.2018 11:35, David Hildenbrand wrote:
> Manually having to use cpu_synchronize_state() is error prone. And as
> Christian Borntraeger discovered, e.g. handle_diag() is currently
> missing a cpu_synchronize_state(), as decode_basedisp_s() uses a
> general purpose register value internally.
> 
> So let's do an overall cpu_synchronize_state(), which fixes at least the
> one mentioned BUG. We will clean up the superfluous cpu_synchronize_state()
> calls later.
> 
> We now also call it (although maybe not neded) for
> - KVM_EXIT_S390_RESET -> s390_reipl_request()
> - KVM_EXIT_DEBUG -> kvm_arch_handle_debug_exit()
> - unmanagable/unimplemented intercepts
> - ICPT_CPU_STOP -> do_stop_interrupt() -> cpu gets halted
> - Scenarios where we inject an operation exception
> - handle_stsi()
> 
> I don't think any of these are performance critical. Especially as we
> have all information directly contained in kvm_run, there are no
> additional IOCTLs to issue on modern kernels.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  target/s390x/kvm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index f570896dc1..fb59d92def 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -1778,6 +1778,8 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
>  
>      qemu_mutex_lock_iothread();
>  
> +    cpu_synchronize_state(cs);

Since we're in kvm.c here, maybe rather call kvm_cpu_synchronize_state()
directly to avoid the wrapper function?

 Thomas

Re: [Qemu-devel] [PATCH v1 for-2.12] s390x/kvm: call cpu_synchronize_state() on every kvm_arch_handle_exit()

[David Hildenbrand]

On 06.04.2018 11:40, Thomas Huth wrote:
> On 06.04.2018 11:35, David Hildenbrand wrote:
>> Manually having to use cpu_synchronize_state() is error prone. And as
>> Christian Borntraeger discovered, e.g. handle_diag() is currently
>> missing a cpu_synchronize_state(), as decode_basedisp_s() uses a
>> general purpose register value internally.
>>
>> So let's do an overall cpu_synchronize_state(), which fixes at least the
>> one mentioned BUG. We will clean up the superfluous cpu_synchronize_state()
>> calls later.
>>
>> We now also call it (although maybe not neded) for
>> - KVM_EXIT_S390_RESET -> s390_reipl_request()
>> - KVM_EXIT_DEBUG -> kvm_arch_handle_debug_exit()
>> - unmanagable/unimplemented intercepts
>> - ICPT_CPU_STOP -> do_stop_interrupt() -> cpu gets halted
>> - Scenarios where we inject an operation exception
>> - handle_stsi()
>>
>> I don't think any of these are performance critical. Especially as we
>> have all information directly contained in kvm_run, there are no
>> additional IOCTLs to issue on modern kernels.
>>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  target/s390x/kvm.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
>> index f570896dc1..fb59d92def 100644
>> --- a/target/s390x/kvm.c
>> +++ b/target/s390x/kvm.c
>> @@ -1778,6 +1778,8 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
>>  
>>      qemu_mutex_lock_iothread();
>>  
>> +    cpu_synchronize_state(cs);
> 
> Since we're in kvm.c here, maybe rather call kvm_cpu_synchronize_state()
> directly to avoid the wrapper function?
> 
>  Thomas
> 

No strong opinion. I can see that kvm_cpu_synchronize_state()
- is not used in target/s390x/kvm.c yet
- is very rarely used in kvm code in general

-- 

Thanks,

David / dhildenb

Re: [Qemu-devel] [PATCH v1 for-2.12] s390x/kvm: call cpu_synchronize_state() on every kvm_arch_handle_exit()

[Cornelia Huck]

On Fri, 6 Apr 2018 11:46:22 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 06.04.2018 11:40, Thomas Huth wrote:
> > On 06.04.2018 11:35, David Hildenbrand wrote:  
> >> Manually having to use cpu_synchronize_state() is error prone. And as
> >> Christian Borntraeger discovered, e.g. handle_diag() is currently
> >> missing a cpu_synchronize_state(), as decode_basedisp_s() uses a
> >> general purpose register value internally.
> >>
> >> So let's do an overall cpu_synchronize_state(), which fixes at least the
> >> one mentioned BUG. We will clean up the superfluous cpu_synchronize_state()
> >> calls later.
> >>
> >> We now also call it (although maybe not neded) for
> >> - KVM_EXIT_S390_RESET -> s390_reipl_request()
> >> - KVM_EXIT_DEBUG -> kvm_arch_handle_debug_exit()
> >> - unmanagable/unimplemented intercepts
> >> - ICPT_CPU_STOP -> do_stop_interrupt() -> cpu gets halted
> >> - Scenarios where we inject an operation exception
> >> - handle_stsi()
> >>
> >> I don't think any of these are performance critical. Especially as we
> >> have all information directly contained in kvm_run, there are no
> >> additional IOCTLs to issue on modern kernels.
> >>
> >> Signed-off-by: David Hildenbrand <david@redhat.com>
> >> ---
> >>  target/s390x/kvm.c | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> >> index f570896dc1..fb59d92def 100644
> >> --- a/target/s390x/kvm.c
> >> +++ b/target/s390x/kvm.c
> >> @@ -1778,6 +1778,8 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
> >>  
> >>      qemu_mutex_lock_iothread();
> >>  
> >> +    cpu_synchronize_state(cs);  
> > 
> > Since we're in kvm.c here, maybe rather call kvm_cpu_synchronize_state()
> > directly to avoid the wrapper function?
> > 
> >  Thomas
> >   
> 
> No strong opinion. I can see that kvm_cpu_synchronize_state()
> - is not used in target/s390x/kvm.c yet
> - is very rarely used in kvm code in general
> 

Let's just go with this one for 2.12? If we want to switch to the kvm_*
variant, we can still do it for 2.13.

Re: [Qemu-devel] [PATCH v1 for-2.12] s390x/kvm: call cpu_synchronize_state() on every kvm_arch_handle_exit()

[Christian Borntraeger]

On 04/06/2018 11:35 AM, David Hildenbrand wrote:
> Manually having to use cpu_synchronize_state() is error prone. And as
> Christian Borntraeger discovered, e.g. handle_diag() is currently
> missing a cpu_synchronize_state(), as decode_basedisp_s() uses a
> general purpose register value internally.
> 
> So let's do an overall cpu_synchronize_state(), which fixes at least the
> one mentioned BUG. We will clean up the superfluous cpu_synchronize_state()
> calls later.
> 
> We now also call it (although maybe not neded) for
> - KVM_EXIT_S390_RESET -> s390_reipl_request()
> - KVM_EXIT_DEBUG -> kvm_arch_handle_debug_exit()
> - unmanagable/unimplemented intercepts
> - ICPT_CPU_STOP -> do_stop_interrupt() -> cpu gets halted
> - Scenarios where we inject an operation exception
> - handle_stsi()
> 
> I don't think any of these are performance critical. Especially as we
> have all information directly contained in kvm_run, there are no
> additional IOCTLs to issue on modern kernels.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>

ok for 2.12.
> ---
>  target/s390x/kvm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index f570896dc1..fb59d92def 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -1778,6 +1778,8 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
> 
>      qemu_mutex_lock_iothread();
> 
> +    cpu_synchronize_state(cs);
> +
>      switch (run->exit_reason) {
>          case KVM_EXIT_S390_SIEIC:
>              ret = handle_intercept(cpu);
> 

Re: [Qemu-devel] [PATCH v1 for-2.12] s390x/kvm: call cpu_synchronize_state() on every kvm_arch_handle_exit()

[Cornelia Huck]

On Fri,  6 Apr 2018 11:35:52 +0200
David Hildenbrand <david@redhat.com> wrote:

> Manually having to use cpu_synchronize_state() is error prone. And as
> Christian Borntraeger discovered, e.g. handle_diag() is currently
> missing a cpu_synchronize_state(), as decode_basedisp_s() uses a
> general purpose register value internally.
> 
> So let's do an overall cpu_synchronize_state(), which fixes at least the
> one mentioned BUG. We will clean up the superfluous cpu_synchronize_state()
> calls later.
> 
> We now also call it (although maybe not neded) for
> - KVM_EXIT_S390_RESET -> s390_reipl_request()
> - KVM_EXIT_DEBUG -> kvm_arch_handle_debug_exit()
> - unmanagable/unimplemented intercepts
> - ICPT_CPU_STOP -> do_stop_interrupt() -> cpu gets halted
> - Scenarios where we inject an operation exception
> - handle_stsi()
> 
> I don't think any of these are performance critical. Especially as we
> have all information directly contained in kvm_run, there are no
> additional IOCTLs to issue on modern kernels.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>  target/s390x/kvm.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index f570896dc1..fb59d92def 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -1778,6 +1778,8 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
>  
>      qemu_mutex_lock_iothread();
>  
> +    cpu_synchronize_state(cs);
> +
>      switch (run->exit_reason) {
>          case KVM_EXIT_S390_SIEIC:
>              ret = handle_intercept(cpu);

Thanks, queued to s390-fixes.