linux-kernel - Re: [PATCH] vfio: Simplify capability helper

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Message-ID: <989db37e-2569-cd6b-fd66-d297d4f8d29e@redhat.com>
Date:   Wed, 13 Dec 2017 16:32:10 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Peter Xu <peterx@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        intel-gvt-dev@...ts.freedesktop.org, aik@...abs.ru,
        kwankhede@...dia.com, zhenyuw@...ux.intel.com, zhi.a.wang@...el.com
Subject: Re: [PATCH] vfio: Simplify capability helper

Hi,

On 13/12/17 16:04, Auger Eric wrote:
> Hi Peter,
> 
> On 13/12/17 07:49, Peter Xu wrote:
>> On Tue, Dec 12, 2017 at 12:59:39PM -0700, Alex Williamson wrote:
>>> The vfio_info_add_capability() helper requires the caller to pass a
>>> capability ID, which it then uses to fill in header fields, assuming
>>> hard coded versions.  This makes for an awkward and rigid interface.
>>> The only thing we want this helper to do is allocate sufficient
>>> space in the caps buffer and chain this capability into the list.
>>> Reduce it to that simple task.
>>>
>>> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
>>
>> Reviewed-by: Peter Xu <peterx@...hat.com>
>>
>> Though during review I had a question related to the function
>> msix_sparse_mmap_cap(): Is it possible that one PCI device BAR is very
>> small (e.g., 4K) that only contains the MSI-X table (and another small
>> PBA area)?  If so, should we just mark that region unmappable instead
>> of setting vfio_region_info_cap_sparse_mmap.nr_areas to 1 in
>> msix_sparse_mmap_cap()?
>>
>> 	/* If MSI-X table is aligned to the start or end, only one area */
>> 	if (((vdev->msix_offset & PAGE_MASK) == 0) ||
>> 	    (PAGE_ALIGN(vdev->msix_offset + vdev->msix_size) >= end))
>> 		nr_areas = 1;
>>
>> Thanks,
>>
> if I understand the code correctly, if the MSI-X table exactly matches
> the BAR, a sparse mmap region is reported with offset/size = 0. Is that
> correct?
> 
> Thanks
> 
> Eric
> 
looks fixed by

[RFC PATCH kernel] vfio-pci: Fix sparse capability when no parts of MSIX
BAR can be mapped

Sorry for the noise.

Thanks

Eric