Re: [PATCH 2/5] qemu-kvm: msix: Only invoke msix_handle_mask_update on changes

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-10-18 14:11, Michael S. Tsirkin wrote:
> On Tue, Oct 18, 2011 at 01:54:23PM +0200, Jan Kiszka wrote:
>> On 2011-10-18 13:43, Michael S. Tsirkin wrote:
>>> On Tue, Oct 18, 2011 at 09:50:51AM +0200, Jan Kiszka wrote:
>>>> Reorganize msix_mmio_writel so that msix_handle_mask_update is only
>>>> called on mask changes. Pass previous config space value to
>>>> msix_write_config so that it can check if a mask change took place.
>>>>
>>>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>>>
>>> What we did in other cases is track the old value in device state.
>>> This makes the API easier to use correctly.
>>> I'm testing the following as a replacement - any comments?
>>
>> No concerns about caching the mask state, but...
>>
>>>
>>> diff --git a/hw/msix.c b/hw/msix.c
>>> index b15bafc..655a600 100644
>>> --- a/hw/msix.c
>>> +++ b/hw/msix.c
>>> @@ -79,6 +79,7 @@ static int msix_add_config(struct PCIDevice *pdev, unsigned short nentries,
>>>      /* Make flags bit writable. */
>>>      pdev->wmask[config_offset + MSIX_CONTROL_OFFSET] |= MSIX_ENABLE_MASK |
>>>  	    MSIX_MASKALL_MASK;
>>> +    pdev->msix_function_masked = false;
>>>      return 0;
>>>  }
>>>  
>>> @@ -117,16 +118,11 @@ static void msix_clr_pending(PCIDevice *dev, int vector)
>>>      *msix_pending_byte(dev, vector) &= ~msix_pending_mask(vector);
>>>  }
>>>  
>>> -static int msix_function_masked(PCIDevice *dev)
>>> -{
>>> -    return dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] & MSIX_MASKALL_MASK;
>>> -}
>>> -
>>>  static int msix_is_masked(PCIDevice *dev, int vector)
>>>  {
>>>      unsigned offset =
>>>          vector * PCI_MSIX_ENTRY_SIZE + PCI_MSIX_ENTRY_VECTOR_CTRL;
>>> -    return msix_function_masked(dev) ||
>>> +    return dev->msix_function_masked ||
>>>  	   dev->msix_table_page[offset] & PCI_MSIX_ENTRY_CTRL_MASKBIT;
>>>  }
>>>  
>>> @@ -144,6 +140,7 @@ void msix_write_config(PCIDevice *dev, uint32_t addr,
>>>  {
>>>      unsigned enable_pos = dev->msix_cap + MSIX_CONTROL_OFFSET;
>>>      int vector;
>>> +    bool fmsk;
>>>  
>>>      if (!range_covers_byte(addr, len, enable_pos)) {
>>>          return;
>>> @@ -155,10 +152,12 @@ void msix_write_config(PCIDevice *dev, uint32_t addr,
>>>  
>>>      pci_device_deassert_intx(dev);
>>>  
>>> -    if (msix_function_masked(dev)) {
>>> +    fmsk = dev->config[dev->msix_cap + MSIX_CONTROL_OFFSET] & MSIX_MASKALL_MASK;
>>> +    if (dev->msix_function_masked == fmsk) {
>>
>> ...this misses MSIX_MASKALL_MASK (but !MSIX_ENABLE_MASK) ->
>> MSIX_ENABLE_MASK.
>>
> 
> Could you clarify please?
>     if (!msix_enabled(dev)) {
>         return;
>     }
> is at start of this function so nothing happens if
> MSIX is disabled.

OK, missed that. But let's have a look again:

ENABLE  -> 0 => msix_function_masked := false
0 -> ENABLE  => msix_function_masked remains false, thus no firing
(while we did fire in the past and should do so in the future)

Jan

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