Re: [Qemu-devel] [PATCH RFC v3 14/14] intel_iommu: enable vfio devices

[Jason Wang <jasowang@redhat.com>]

On 2017年01月16日 17:18, Peter Xu wrote:
>>>   static void vtd_iotlb_page_invalidate(IntelIOMMUState *s, uint16_t domain_id,
>>>                                         hwaddr addr, uint8_t am)
>>>   {
>>> @@ -1222,6 +1251,7 @@ static void vtd_iotlb_page_invalidate(IntelIOMMUState *s, uint16_t domain_id,
>>>       info.addr = addr;
>>>       info.mask = ~((1 << am) - 1);
>>>       g_hash_table_foreach_remove(s->iotlb, vtd_hash_remove_by_page, &info);
>>> +    vtd_iotlb_page_invalidate_notify(s, domain_id, addr, am);
>> Is the case of GLOBAL or DSI flush missed, or we don't care it at all?
> IMHO we don't. For device assignment, since we are having CM=1 here,
> we should have explicit page invalidations even if guest sends
> global/domain invalidations.
>
> Thanks,
>
> -- peterx

Is this spec required? Btw, it looks to me that both DSI and GLOBAL are 
indeed explicit flush.

Just have a quick go through on driver codes and find this something 
interesting in intel_iommu_flush_iotlb_psi():

...
     /*
      * Fallback to domain selective flush if no PSI support or the size is
      * too big.
      * PSI requires page size to be 2 ^ x, and the base address is 
naturally
      * aligned to the size
      */
     if (!cap_pgsel_inv(iommu->cap) || mask > cap_max_amask_val(iommu->cap))
         iommu->flush.flush_iotlb(iommu, did, 0, 0,
                         DMA_TLB_DSI_FLUSH);
     else
         iommu->flush.flush_iotlb(iommu, did, addr | ih, mask,
                         DMA_TLB_PSI_FLUSH);
...

It looks like DSI_FLUSH is possible even for CM on.

And in flush_unmaps():

...
         /* In caching mode, global flushes turn emulation expensive */
         if (!cap_caching_mode(iommu->cap))
             iommu->flush.flush_iotlb(iommu, 0, 0, 0,
                      DMA_TLB_GLOBAL_FLUSH);
...

If I understand the comments correctly, GLOBAL is ok for CM too (though 
the code did not do it for performance reason).

Thanks