linux-kernel - Re: [PATCH v9 10/11] vfio/pci: Add dma-buf export support for MMIO regions

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Message-Id: <cd6f8c6b-6950-4b06-8f2d-bb4ead660ead@app.fastmail.com>
Date: Thu, 20 Nov 2025 17:40:15 -0700
From: "Alex Williamson" <alex@...zbot.org>
To: "Jason Gunthorpe" <jgg@...pe.ca>
Cc: "Leon Romanovsky" <leon@...nel.org>,
 "Bjorn Helgaas" <bhelgaas@...gle.com>,
 "Logan Gunthorpe" <logang@...tatee.com>, "Jens Axboe" <axboe@...nel.dk>,
 "Robin Murphy" <robin.murphy@....com>, "Joerg Roedel" <joro@...tes.org>,
 "Will Deacon" <will@...nel.org>,
 "Marek Szyprowski" <m.szyprowski@...sung.com>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Jonathan Corbet" <corbet@....net>,
 "Sumit Semwal" <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 "Kees Cook" <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 "Ankit Agrawal" <ankita@...dia.com>, "Yishai Hadas" <yishaih@...dia.com>,
 "Shameer Kolothum" <skolothumtho@...dia.com>,
 "Kevin Tian" <kevin.tian@...el.com>,
 "Krishnakant Jaju" <kjaju@...dia.com>, "Matt Ochs" <mochs@...dia.com>,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-block@...r.kernel.org, iommu@...ts.linux.dev, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, linux-media@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org,
 kvm@...r.kernel.org, linux-hardening@...r.kernel.org,
 "Vivek Kasireddy" <vivek.kasireddy@...el.com>
Subject: Re: [PATCH v9 10/11] vfio/pci: Add dma-buf export support for MMIO regions

On Thu, Nov 20, 2025, at 5:23 PM, Jason Gunthorpe wrote:
> On Thu, Nov 20, 2025 at 05:04:13PM -0700, Alex Williamson wrote:
>
>> @@ -2501,7 +2501,7 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
>>  err_undo:
>>         list_for_each_entry_from_reverse(vdev, &dev_set->device_list,
>>                                          vdev.dev_set_list) {
>> -               if (__vfio_pci_memory_enabled(vdev))
>> +               if (vdev->vdev.open_count && __vfio_pci_memory_enabled(vdev))
>>                         vfio_pci_dma_buf_move(vdev, false);
>>                 up_write(&vdev->memory_lock);
>>         }
>> 
>> Any other suggestions?  This should be the only reset path with this
>> nuance of affecting non-opened devices.  Thanks,
>
> Seems reasonable, but should it be in __vfio_pci_memory_enabled() just
> to be robust?

__vfio_pci_memory_enabled() currently only requires holding memory_lock, I don't think we want to create a dependency on dev_set->lock for this unique call path.  Thanks,

Alex