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([2a01:e0a:280:24f0:576b:abc6:6396:ed4a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e354e07f2sm82406445e9.9.2025.09.29.00.50.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Sep 2025 00:50:07 -0700 (PDT) Message-ID: <29f56a9a-025d-458d-b37e-828150f8255d@redhat.com> Date: Mon, 29 Sep 2025 09:50:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] vfio: Remove workaround for kernel DMA unmap overflow bug To: qemu-devel@nongnu.org Cc: Alex Williamson , Peter Xu References: <20250926085423.375547-1-clg@redhat.com> From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= Content-Language: en-US, fr Autocrypt: addr=clg@redhat.com; keydata= xsFNBFu8o3UBEADP+oJVJaWm5vzZa/iLgpBAuzxSmNYhURZH+guITvSySk30YWfLYGBWQgeo 8NzNXBY3cH7JX3/a0jzmhDc0U61qFxVgrPqs1PQOjp7yRSFuDAnjtRqNvWkvlnRWLFq4+U5t yzYe4SFMjFb6Oc0xkQmaK2flmiJNnnxPttYwKBPd98WfXMmjwAv7QfwW+OL3VlTPADgzkcqj 53bfZ4VblAQrq6Ctbtu7JuUGAxSIL3XqeQlAwwLTfFGrmpY7MroE7n9Rl+hy/kuIrb/TO8n0 ZxYXvvhT7OmRKvbYuc5Jze6o7op/bJHlufY+AquYQ4dPxjPPVUT/DLiUYJ3oVBWFYNbzfOrV RxEwNuRbycttMiZWxgflsQoHF06q/2l4ttS3zsV4TDZudMq0TbCH/uJFPFsbHUN91qwwaN/+ gy1j7o6aWMz+Ib3O9dK2M/j/O/Ube95mdCqN4N/uSnDlca3YDEWrV9jO1mUS/ndOkjxa34ia 70FjwiSQAsyIwqbRO3CGmiOJqDa9qNvd2TJgAaS2WCw/TlBALjVQ7AyoPEoBPj31K74Wc4GS Rm+FSch32ei61yFu6ACdZ12i5Edt+To+hkElzjt6db/UgRUeKfzlMB7PodK7o8NBD8outJGS tsL2GRX24QvvBuusJdMiLGpNz3uqyqwzC5w0Fd34E6G94806fwARAQABzSJDw6lkcmljIExl IEdvYXRlciA8Y2xnQHJlZGhhdC5jb20+wsGRBBMBCAA7FiEEoPZlSPBIlev+awtgUaNDx8/7 7KEFAmTLlVECGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgkQUaNDx8/77KG0eg// S0zIzTcxkrwJ/9XgdcvVTnXLVF9V4/tZPfB7sCp8rpDCEseU6O0TkOVFoGWM39sEMiQBSvyY lHrP7p7E/JYQNNLh441MfaX8RJ5Ul3btluLapm8oHp/vbHKV2IhLcpNCfAqaQKdfk8yazYhh EdxTBlzxPcu+78uE5fF4wusmtutK0JG0sAgq0mHFZX7qKG6LIbdLdaQalZ8CCFMKUhLptW71 xe+aNrn7hScBoOj2kTDRgf9CE7svmjGToJzUxgeh9mIkxAxTu7XU+8lmL28j2L5uNuDOq9vl hM30OT+pfHmyPLtLK8+GXfFDxjea5hZLF+2yolE/ATQFt9AmOmXC+YayrcO2ZvdnKExZS1o8 VUKpZgRnkwMUUReaF/mTauRQGLuS4lDcI4DrARPyLGNbvYlpmJWnGRWCDguQ/LBPpbG7djoy k3NlvoeA757c4DgCzggViqLm0Bae320qEc6z9o0X0ePqSU2f7vcuWN49Uhox5kM5L86DzjEQ RHXndoJkeL8LmHx8DM+kx4aZt0zVfCHwmKTkSTQoAQakLpLte7tWXIio9ZKhUGPv/eHxXEoS 0rOOAZ6np1U/xNR82QbF9qr9TrTVI3GtVe7Vxmff+qoSAxJiZQCo5kt0YlWwti2fFI4xvkOi V7lyhOA3+/3oRKpZYQ86Frlo61HU3r6d9wzOwU0EW7yjdQEQALyDNNMw/08/fsyWEWjfqVhW pOOrX2h+z4q0lOHkjxi/FRIRLfXeZjFfNQNLSoL8j1y2rQOs1j1g+NV3K5hrZYYcMs0xhmrZ KXAHjjDx7FW3sG3jcGjFW5Xk4olTrZwFsZVUcP8XZlArLmkAX3UyrrXEWPSBJCXxDIW1hzwp bV/nVbo/K9XBptT/wPd+RPiOTIIRptjypGY+S23HYBDND3mtfTz/uY0Jytaio9GETj+fFis6 TxFjjbZNUxKpwftu/4RimZ7qL+uM1rG1lLWc9SPtFxRQ8uLvLOUFB1AqHixBcx7LIXSKZEFU CSLB2AE4wXQkJbApye48qnZ09zc929df5gU6hjgqV9Gk1rIfHxvTsYltA1jWalySEScmr0iS YBZjw8Nbd7SxeomAxzBv2l1Fk8fPzR7M616dtb3Z3HLjyvwAwxtfGD7VnvINPbzyibbe9c6g LxYCr23c2Ry0UfFXh6UKD83d5ybqnXrEJ5n/t1+TLGCYGzF2erVYGkQrReJe8Mld3iGVldB7 JhuAU1+d88NS3aBpNF6TbGXqlXGF6Yua6n1cOY2Yb4lO/mDKgjXd3aviqlwVlodC8AwI0Sdu jWryzL5/AGEU2sIDQCHuv1QgzmKwhE58d475KdVX/3Vt5I9kTXpvEpfW18TjlFkdHGESM/Jx IqVsqvhAJkalABEBAAHCwV8EGAECAAkFAlu8o3UCGwwACgkQUaNDx8/77KEhwg//WqVopd5k 8hQb9VVdk6RQOCTfo6wHhEqgjbXQGlaxKHoXywEQBi8eULbeMQf5l4+tHJWBxswQ93IHBQjK yKyNr4FXseUI5O20XVNYDJZUrhA4yn0e/Af0IX25d94HXQ5sMTWr1qlSK6Zu79lbH3R57w9j hQm9emQEp785ui3A5U2Lqp6nWYWXz0eUZ0Tad2zC71Gg9VazU9MXyWn749s0nXbVLcLS0yop s302Gf3ZmtgfXTX/W+M25hiVRRKCH88yr6it+OMJBUndQVAA/fE9hYom6t/zqA248j0QAV/p LHH3hSirE1mv+7jpQnhMvatrwUpeXrOiEw1nHzWCqOJUZ4SY+HmGFW0YirWV2mYKoaGO2YBU wYF7O9TI3GEEgRMBIRT98fHa0NPwtlTktVISl73LpgVscdW8yg9Gc82oe8FzU1uHjU8b10lU XOMHpqDDEV9//r4ZhkKZ9C4O+YZcTFu+mvAY3GlqivBNkmYsHYSlFsbxc37E1HpTEaSWsGfA HQoPn9qrDJgsgcbBVc1gkUT6hnxShKPp4PlsZVMNjvPAnr5TEBgHkk54HQRhhwcYv1T2QumQ izDiU6iOrUzBThaMhZO3i927SG2DwWDVzZltKrCMD1aMPvb3NU8FOYRhNmIFR3fcalYr+9gD uVKe8BVz4atMOoktmt0GWTOC8P4= In-Reply-To: <20250926085423.375547-1-clg@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.539, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=-1, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 9/26/25 10:54, Cédric Le Goater wrote: > A kernel bug was introduced in Linux v4.15 via commit 71a7d3d78e3c > ("vfio/type1: Check for address space wrap-around on unmap"), which > added a test for address space wrap-around in the vfio DMA unmap path. > Unfortunately, due to an integer overflow, the kernel would > incorrectly detect an unmap of the last page in the 64-bit address > space as a wrap-around, causing the unmap to fail with -EINVAL. > > A QEMU workaround was introduced in commit 567d7d3e6be5 ("vfio/common: > Work around kernel overflow bug in DMA unmap") to retry the unmap, > excluding the final page of the range. > > The kernel bug was then fixed in Linux v5.0 via commit 58fec830fc19 > ("vfio/type1: Fix dma_unmap wrap-around check"). Since the oldest > supported LTS kernel is now v5.4, kernels affected by this bug are > considered deprecated, and the workaround is no longer necessary. > > This change reverts 567d7d3e6be5, removing the workaround. > > Link: https://bugzilla.redhat.com/show_bug.cgi?id=1662291 > Signed-off-by: Cédric Le Goater > --- > hw/vfio/container-legacy.c | 20 +------------------- > hw/vfio/trace-events | 1 - > 2 files changed, 1 insertion(+), 20 deletions(-) > > diff --git a/hw/vfio/container-legacy.c b/hw/vfio/container-legacy.c > index c0f87f774a00805cab4a8f3b3386ddd99c3d9111..25a15ea8674c159b7e624425c52953240b8c1179 100644 > --- a/hw/vfio/container-legacy.c > +++ b/hw/vfio/container-legacy.c > @@ -147,25 +147,7 @@ static int vfio_legacy_dma_unmap_one(const VFIOContainer *bcontainer, > need_dirty_sync = true; > } > > - while (ioctl(container->fd, VFIO_IOMMU_UNMAP_DMA, &unmap)) { > - /* > - * The type1 backend has an off-by-one bug in the kernel (71a7d3d78e3c > - * v4.15) where an overflow in its wrap-around check prevents us from > - * unmapping the last page of the address space. Test for the error > - * condition and re-try the unmap excluding the last page. The > - * expectation is that we've never mapped the last page anyway and this > - * unmap request comes via vIOMMU support which also makes it unlikely > - * that this page is used. This bug was introduced well after type1 v2 > - * support was introduced, so we shouldn't need to test for v1. A fix > - * is queued for kernel v5.0 so this workaround can be removed once > - * affected kernels are sufficiently deprecated. > - */ > - if (errno == EINVAL && unmap.size && !(unmap.iova + unmap.size) && > - container->iommu_type == VFIO_TYPE1v2_IOMMU) { > - trace_vfio_legacy_dma_unmap_overflow_workaround(); > - unmap.size -= 1ULL << ctz64(bcontainer->pgsizes); > - continue; > - } > + if (ioctl(container->fd, VFIO_IOMMU_UNMAP_DMA, &unmap)) { > return -errno; > } > > diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events > index e3d571f8c845dad85de5738f8ca768bdfc336252..7496e1b64b5de0168974a251eab698399a6a1d54 100644 > --- a/hw/vfio/trace-events > +++ b/hw/vfio/trace-events > @@ -112,7 +112,6 @@ vfio_container_disconnect(int fd) "close container->fd=%d" > vfio_group_put(int fd) "close group->fd=%d" > vfio_device_get(const char * name, unsigned int flags, unsigned int num_regions, unsigned int num_irqs) "Device %s flags: %u, regions: %u, irqs: %u" > vfio_device_put(int fd) "close vdev->fd=%d" > -vfio_legacy_dma_unmap_overflow_workaround(void) "" > > # region.c > vfio_region_write(const char *name, int index, uint64_t addr, uint64_t data, unsigned size) " (%s:region%d+0x%"PRIx64", 0x%"PRIx64 ", %d)" Applied to vfio-next. Thanks, C.