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(e.d.c.5.4.7.0.e.f.a.2.f.e.2.0.1.4.d.3.1.6.b.8.0.0.b.8.0.1.0.0.2.ip6.arpa. [2001:8b0:8b6:13d4:102e:f2af:e074:5cde]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45052483166sm13251331f8f.7.2026.05.06.08.55.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 May 2026 08:55:28 -0700 (PDT) Message-ID: Date: Wed, 6 May 2026 16:55:27 +0100 Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/9] vfio/pci: Fix vfio_pci_dma_buf_cleanup() double-put Content-Language: en-GB To: Leon Romanovsky Cc: Alex Williamson , Jason Gunthorpe , Alex Mastro , =?UTF-8?Q?Christian_K=C3=B6nig?= , Mahmoud Adam , David Matlack , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Sumit Semwal , Kevin Tian , Ankit Agrawal , Pranjal Shrivastava , Alistair Popple , Vivek Kasireddy , linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, kvm@vger.kernel.org, =?UTF-8?Q?Carlos_L=C3=B3pez?= References: <20260416131815.2729131-1-mattev@meta.com> <20260416131815.2729131-2-mattev@meta.com> <20260501131236.278ac431@shazbot.org> <9304aada-ee84-4cf2-a1d7-82313eda07aa@meta.com> <20260506152937.GJ11063@unreal> From: Matt Evans In-Reply-To: <20260506152937.GJ11063@unreal> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA2MDE1NiBTYWx0ZWRfX21C20H/X5wuz 27Zc4LrBygzBAlynLZMTZOc2YWSH9UXu6PSXZb8D7Qs5oul/6YWX448hYaWUYMvQoXY7nJ2erxU jCmuN8BTadFK06MNhXftNHfSM9oG9PrABYdQOciEwPW2XjaC+T/3upvpysDcB79UkzlKvpUBkj9 /OYOg9QGmhGTRxEv7fs3qEC9NkOcsLvqJXZ48sQ59X6KO0axl4scjpIiTim/H6ihzCTsQYphsJS j6MgU4UtJtFF4llOXQev7wery80ekF+MeWmyD9OfhyBQGKPPYhWkNfWtK/WrbJLkVeenJNzqw/T 5Zc05plq5+qSzvJSu1E/5OfxJIOaAPmtFbvRoNmYM0Ka2q8pjT8yOGOxch7DJAsW50FXNCC+UBw nmRkspXEF6lGk1wN3Mm38mno1Gw1WLfCF5L5NR+k6gwn8L7S+20rg7uqc0sAJITh44IAVbkb/pV ZaNsQOdtjzTnZDp81bw== X-Proofpoint-GUID: hLa4K_e3jnfrrGmcBMLG58L0StresFgT X-Authority-Analysis: v=2.4 cv=GKs41ONK c=1 sm=1 tr=0 ts=69fb6473 cx=c_pps a=I6ewnrIBtnKHmb6SxpX7Vg==:117 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=7x6HtfJdh03M6CCDgxCd:22 a=wpfVPzegXHpEFt3DAXn9:22 a=VwQbUJbxAAAA:8 a=UqCG9HQmAAAA:8 a=Ikd4Dj_1AAAA:8 a=VabnemYjAAAA:8 a=bm6tUXqWTanbjDFH1akA:9 a=QEXdDO2ut3YA:10 a=MqNruPmfsT8GavliLQMe:22 a=gKebqoRLp9LExxC7YDUY:22 X-Proofpoint-ORIG-GUID: hLa4K_e3jnfrrGmcBMLG58L0StresFgT X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-06_01,2026-05-06_01,2025-10-01_01 Hi Leon, On 06/05/2026 16:29, Leon Romanovsky wrote: > > On Wed, May 06, 2026 at 02:53:31PM +0100, Matt Evans wrote: >> Hi Alex, >> >> On 01/05/2026 20:12, Alex Williamson wrote: >>> >>> On Thu, 16 Apr 2026 06:17:44 -0700 >>> Matt Evans wrote: >>> >>>> vfio_pci_dma_buf_cleanup() assumed all VFIO device DMABUFs need to be >>>> revoked. However, if vfio_pci_dma_buf_move() revokes DMABUFs before >>>> the fd/device closes, then vfio_pci_dma_buf_cleanup() would do a >>>> second/underflowing kref_put() then wait_for_completion() on a >>>> completion that never fires. Fixed by predicating on revocation >>>> status. >>>> >>>> This could happen if PCI_COMMAND_MEMORY is cleared before closing the >>>> device fd (but the scenario is more likely to hit when future commits >>>> add more methods to revoke DMABUFs). >>>> >>>> Fixes: 1a8a5227f2299 ("vfio: Wait for dma-buf invalidation to complete") >>>> Signed-off-by: Matt Evans >>>> --- >>>> >>>> (Just a fix, but later "vfio/pci: Convert BAR mmap() to use a DMABUF" >>>> and "vfio/pci: Permanently revoke a DMABUF on request" depend on this >>>> context, so including in this series.) >>> >>> We really need a fix for this split out from this series, It's already >>> been shown[1] that this is trivially reachable. Carlos proposed[2] a >>> similar solution to the one below. I was concurrently working on the >>> issued and suggested an alternative[3]. Let's pick a solution for >>> 7.1-rc. Thanks, >> >> It looks like [3] is progressing, so I'll drop this one when I can rebase >> onto it. >> >> I noticed [3] removes the dma_resv_lock(priv->dmabuf->resv) around the >> priv->vdev = NULL, and this series' vfio_pci_mmap_huge_fault() relies on >> vdev only changing whilst resv is held to resolve a race between a fault and >> cleanup (see patch 7 of this series). The handler takes resv so that it can >> stably test vdev in order to take memory_lock. > > I think that you should rely on priv->revoked and not on priv->vdev. Needs both unfortunately, as the fault handler ultimately needs to take vdev->memory_lock. Matt > > Thanks > >> >> Must your fix change vdev outside of holding resv? I'm still sketching >> alternatives; at first glance perhaps the fault handler could rely on vdev >> being valid if !revoked, which can be tested holding [only] resv. >> >> >> Thanks, >> >> Matt >> >>> >>> Alex >>> >>> [1]https://lore.kernel.org/all/GVXPR02MB12019AA6014F27EF5D773E89BFB372@GVXPR02MB12019.eurprd02.prod.outlook.com/ >>> [2]https://lore.kernel.org/all/20260429182736.409323-2-clopez@suse.de/ >>> [3]https://lore.kernel.org/all/20260429142242.70f746b4@nvidia.com/ >>> >>>> drivers/vfio/pci/vfio_pci_dmabuf.c | 9 +++++++-- >>>> 1 file changed, 7 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/vfio/pci/vfio_pci_dmabuf.c b/drivers/vfio/pci/vfio_pci_dmabuf.c >>>> index 281ba7d69567..04478b7415a0 100644 >>>> --- a/drivers/vfio/pci/vfio_pci_dmabuf.c >>>> +++ b/drivers/vfio/pci/vfio_pci_dmabuf.c >>>> @@ -395,20 +395,25 @@ void vfio_pci_dma_buf_cleanup(struct vfio_pci_core_device *vdev) >>>> down_write(&vdev->memory_lock); >>>> list_for_each_entry_safe(priv, tmp, &vdev->dmabufs, dmabufs_elm) { >>>> + bool was_revoked; >>>> + >>>> if (!get_file_active(&priv->dmabuf->file)) >>>> continue; >>>> dma_resv_lock(priv->dmabuf->resv, NULL); >>>> list_del_init(&priv->dmabufs_elm); >>>> priv->vdev = NULL; >>>> + was_revoked = priv->revoked; >>>> priv->revoked = true; >>>> dma_buf_invalidate_mappings(priv->dmabuf); >>>> dma_resv_wait_timeout(priv->dmabuf->resv, >>>> DMA_RESV_USAGE_BOOKKEEP, false, >>>> MAX_SCHEDULE_TIMEOUT); >>>> dma_resv_unlock(priv->dmabuf->resv); >>>> - kref_put(&priv->kref, vfio_pci_dma_buf_done); >>>> - wait_for_completion(&priv->comp); >>>> + if (!was_revoked) { >>>> + kref_put(&priv->kref, vfio_pci_dma_buf_done); >>>> + wait_for_completion(&priv->comp); >>>> + } >>>> vfio_device_put_registration(&vdev->vdev); >>>> fput(priv->dmabuf->file); >>>> } >>> >>