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([2a01:e0a:165:d60:bbdd:3c5e:7d8b:3f72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43186c0e0d5sm15476925e9.31.2024.10.23.05.44.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Oct 2024 05:44:20 -0700 (PDT) Message-ID: Date: Wed, 23 Oct 2024 14:44:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] vfio/helpers: Align mmaps To: Alex Williamson , qemu-devel@nongnu.org Cc: peterx@redhat.com References: <20241022200830.4129598-1-alex.williamson@redhat.com> <20241022200830.4129598-3-alex.williamson@redhat.com> Content-Language: en-US, fr From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= 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: <20241022200830.4129598-3-alex.williamson@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.263, 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_H2=-1.697, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=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 10/22/24 22:08, Alex Williamson wrote: > Thanks to work by Peter Xu, support is introduced in Linux v6.12 to > allow pfnmap insertions at PMD and PUD levels of the page table. This > means that provided a properly aligned mmap, the vfio driver is able > to map MMIO at significantly larger intervals than PAGE_SIZE. For > example on x86_64 (the only architecture currently supporting huge > pfnmaps for PUD), rather than 4KiB mappings, we can map device MMIO > using 2MiB and even 1GiB page table entries. > > Typically mmap will already provide PMD aligned mappings, so devices > with moderately sized MMIO ranges, even GPUs with standard 256MiB BARs, > will already take advantage of this support. However in order to better > support devices exposing multi-GiB MMIO, such as 3D accelerators or GPUs > with resizable BARs enabled, we need to manually align the mmap. > > There doesn't seem to be a way for userspace to easily learn about PMD > and PUD mapping level sizes, therefore this takes the simple approach > to align the mapping to the power-of-two size of the region, up to 1GiB, > which is currently the maximum alignment we care about. Couldn't we inspect /sys/kernel/mm/hugepages/ to get the sizes ? > Cc: Peter Xu > Signed-off-by: Alex Williamson anyhow, Reviewed-by: Cédric Le Goater Thanks, C. > --- > hw/vfio/helpers.c | 32 ++++++++++++++++++++++++++++++-- > 1 file changed, 30 insertions(+), 2 deletions(-) > > diff --git a/hw/vfio/helpers.c b/hw/vfio/helpers.c > index b9e606e364a2..913796f437f8 100644 > --- a/hw/vfio/helpers.c > +++ b/hw/vfio/helpers.c > @@ -27,6 +27,7 @@ > #include "trace.h" > #include "qapi/error.h" > #include "qemu/error-report.h" > +#include "qemu/units.h" > #include "monitor/monitor.h" > > /* > @@ -406,8 +407,35 @@ int vfio_region_mmap(VFIORegion *region) > prot |= region->flags & VFIO_REGION_INFO_FLAG_WRITE ? PROT_WRITE : 0; > > for (i = 0; i < region->nr_mmaps; i++) { > - region->mmaps[i].mmap = mmap(NULL, region->mmaps[i].size, prot, > - MAP_SHARED, region->vbasedev->fd, > + size_t align = MIN(1ULL << ctz64(region->mmaps[i].size), 1 * GiB); > + void *map_base, *map_align; > + > + /* > + * Align the mmap for more efficient mapping in the kernel. Ideally > + * we'd know the PMD and PUD mapping sizes to use as discrete alignment > + * intervals, but we don't. As of Linux v6.12, the largest PUD size > + * supporting huge pfnmap is 1GiB (ARCH_SUPPORTS_PUD_PFNMAP is only set > + * on x86_64). Align by power-of-two size, capped at 1GiB. > + * > + * NB. qemu_memalign() and friends actually allocate memory, whereas > + * the region size here can exceed host memory, therefore we manually > + * create an oversized anonymous mapping and clean it up for alignment. > + */ > + map_base = mmap(0, region->mmaps[i].size + align, PROT_NONE, > + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > + if (map_base == MAP_FAILED) { > + ret = -errno; > + goto no_mmap; > + } > + > + map_align = (void *)ROUND_UP((uintptr_t)map_base, (uintptr_t)align); > + munmap(map_base, map_align - map_base); > + munmap(map_align + region->mmaps[i].size, > + align - (map_align - map_base)); > + > + region->mmaps[i].mmap = mmap(map_align, region->mmaps[i].size, prot, > + MAP_SHARED | MAP_FIXED, > + region->vbasedev->fd, > region->fd_offset + > region->mmaps[i].offset); > if (region->mmaps[i].mmap == MAP_FAILED) {