Re: [Qemu-devel] [PATCH v2 21/42] ivshmem: Clean up MSI-X conditions

[Markus Armbruster]

Marc-André Lureau <address@hidden> writes:

> Hi
>
> On Mon, Mar 7, 2016 at 8:25 PM, Markus Armbruster <address@hidden> wrote:
>> There are three predicates related to MSI-X:
>>
>> * ivshmem_has_feature(s, IVSHMEM_MSI) is true unless the non-MSI-X
>>   variant of the device is selected with msi=off.
>>
>> * msix_present() is true when the device has the PCI capability MSI-X.
>>   It's initially false, and becomes true during successful realize of
>>   the MSI-X variant of the device.  Thus, it's the same as
>>   ivshmem_has_feature(s, IVSHMEM_MSI) for realized devices.
>>
>> * msix_enabled() is true when msix_present() is true and guest software
>>   has enabled MSI-X.
>>
>> Code that differs between the non-MSI-X and the MSI-X variant of the
>> device needs to be guarded by ivshmem_has_feature(s, IVSHMEM_MSI) or
>> by msix_present(), except the latter works only for realized devices.
>>
>> Code that depends on whether MSI-X is in use needs to be guarded with
>> msix_enabled().
>>
>> Code review led me to two minor messes:
>>
>> * ivshmem_vector_notify() calls msix_notify() even when
>>   !msix_enabled(), unlike most other MSI-X-capable devices.  As far as
>>   I can tell, msix_notify() does nothing when !msix_enabled().  Add
>>   the guard anyway.
>>
>> * Most callers of ivshmem_use_msix() guard it with
>>   ivshmem_has_feature(s, IVSHMEM_MSI).  Not necessary, because
>>   ivshmem_use_msix() does nothing when !msix_present().  That's
>>   ivshmem's only use of msix_present(), though.  Rename
>>   ivshmem_use_msix() to ivshmem_vector_use(), replace msix_present()
>>   by ivshmem_has_feature() there, and drop the redundant guards.
>>
>> Signed-off-by: Markus Armbruster <address@hidden>
>> ---
>>  hw/misc/ivshmem.c | 22 +++++++++-------------
>>  1 file changed, 9 insertions(+), 13 deletions(-)
>>
>> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
>> index 7191914..cfea151 100644
>> --- a/hw/misc/ivshmem.c
>> +++ b/hw/misc/ivshmem.c
>> @@ -274,7 +274,9 @@ static void ivshmem_vector_notify(void *opaque)
>>
>>      IVSHMEM_DPRINTF("interrupt on vector %p %d\n", pdev, vector);
>>      if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
>> -        msix_notify(pdev, vector);
>> +        if (msix_enabled(pdev)) {
>> +            msix_notify(pdev, vector);
>> +        }
>>      } else {
>>          ivshmem_IntrStatus_write(s, 1);
>>      }
>> @@ -712,13 +714,12 @@ static void ivshmem_check_version(void *opaque, const 
>> uint8_t * buf, int size)
>>  /* Select the MSI-X vectors used by device.
>>   * ivshmem maps events to vectors statically, so
>>   * we just enable all vectors on init and after reset. */
>> -static void ivshmem_use_msix(IVShmemState * s)
>> +static void ivshmem_vector_use(IVShmemState *s)
>>  {
>>      PCIDevice *d = PCI_DEVICE(s);
>>      int i;
>>
>> -    IVSHMEM_DPRINTF("%s, msix present: %d\n", __func__, msix_present(d));
>> -    if (!msix_present(d)) {
>> +    if (!ivshmem_has_feature(s, IVSHMEM_MSI)) {
>>          return;
>>      }
>>
>> @@ -733,7 +734,7 @@ static void ivshmem_reset(DeviceState *d)
>>
>>      s->intrstatus = 0;
>>      s->intrmask = 0;
>> -    ivshmem_use_msix(s);
>> +    ivshmem_vector_use(s);
>>  }
>>
>>  static int ivshmem_setup_interrupts(IVShmemState *s)
>> @@ -747,9 +748,9 @@ static int ivshmem_setup_interrupts(IVShmemState *s)
>>          }
>>
>>          IVSHMEM_DPRINTF("msix initialized (%d vectors)\n", s->vectors);
>> -        ivshmem_use_msix(s);
>>      }
>>
>> +    ivshmem_vector_use(s);
>>      return 0;
>>  }
>>
>> @@ -1034,12 +1035,7 @@ static int ivshmem_pre_load(void *opaque)
>>
>>  static int ivshmem_post_load(void *opaque, int version_id)
>>  {
>> -    IVShmemState *s = opaque;
>> -
>> -    if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
>> -        ivshmem_use_msix(s);
>> -    }
>> -
>> +    ivshmem_vector_use(opaque);
>>      return 0;
>>  }
>>
>> @@ -1067,11 +1063,11 @@ static int ivshmem_load_old(QEMUFile *f, void 
>> *opaque, int version_id)
>>
>>      if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
>>          msix_load(pdev, f);
>> -        ivshmem_use_msix(s);
>>      } else {
>>          s->intrstatus = qemu_get_be32(f);
>>          s->intrmask = qemu_get_be32(f);
>>      }
>> +    ivshmem_vector_use(s);
>>
>
> Sorry I didn't reply to your previous mail (which was slightly
> confusing due to wrong naming), yes I think calling it
> ivshmem_msix_vectors_use() inside the msix block is better (#2 from
> your reply).

I'll give it a try and see how it comes out.

> Other than that
>
> Reviewed-by: Marc-André Lureau <address@hidden>

Thanks!