Re: [RFC PATCH v3 7/8] vfio/type1: Add selective DMA faulting support

[Shenming Lu]

On 2021/5/19 2:58, Alex Williamson wrote:
> On Fri, 9 Apr 2021 11:44:19 +0800
> Shenming Lu <lushenming@xxxxxxxxxx> wrote:
> 
>> Some devices only allow selective DMA faulting. Similar to the selective
>> dirty page tracking, the vendor driver can call vfio_pin_pages() to
>> indicate the non-faultable scope, we add a new struct vfio_range to
>> record it, then when the IOPF handler receives any page request out
>> of the scope, we can directly return with an invalid response.
> 
> Seems like this highlights a deficiency in the design, that the user
> can't specify mappings as iopf enabled or disabled.  Also, if the
> vendor driver has pinned pages within the range, shouldn't that prevent
> them from faulting in the first place?  Why do we need yet more
> tracking structures?  Pages pinned by the vendor driver need to count
> against the user's locked memory limits regardless of iopf.  Thanks,

Currently we only have a vfio_pfn struct to track the external pinned pages
(single page granularity), so I add a vfio_range struct for efficient lookup.

Yeah, by this patch, for the non-pinned scope, we can directly return INVALID,
but for the pinned(non-faultable) scope, tracking the pinned range doesn't seem
to help more...

Thanks,
Shenming

> 
> Alex
> 
> .
>