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Diffstat (limited to 'results/scraper/launchpad-without-comments/2025586')
| -rw-r--r-- | results/scraper/launchpad-without-comments/2025586 | 43 |
1 files changed, 43 insertions, 0 deletions
diff --git a/results/scraper/launchpad-without-comments/2025586 b/results/scraper/launchpad-without-comments/2025586 new file mode 100644 index 000000000..d908fffcf --- /dev/null +++ b/results/scraper/launchpad-without-comments/2025586 @@ -0,0 +1,43 @@ +Align the iov length to the logical block size + +[Impact] +When the logical block size of the virtual block device is smaller than the block device it is backed by on the host, +qemu encounters a situation where it needs to bounce unaligned buffers during the use of direct IO. +In the past, the logical block size happened to align with the memory page offset, leading qemu to mistakenly use the memory offset as the block size. +However, a kernel commit b1a000d3b8ec resolved this issue by separating memory alignment from the logical block size. +As a result, qemu now has an incorrect understanding of the minimum vector size. + +[Fix] +Upstream commit 25474d90aa50 fixed this issue. +========== +Author: Keith Busch <email address hidden> +CommitDate: Fri Sep 30 18:43:44 2022 +0200 + + block: use the request length for iov alignment + + An iov length needs to be aligned to the logical block size, which may + be larger than the memory alignment. + + Tested-by: Jens Axboe <email address hidden> + Signed-off-by: Keith Busch <email address hidden> + Message-Id: <email address hidden> + Reviewed-by: Kevin Wolf <email address hidden> + Signed-off-by: Kevin Wolf <email address hidden> +========== + +[Test Plan] +1. Get a ubuntu image and convert it to RAW format +wget https://cloud-images.ubuntu.com/jammy/current/jammy-server-cloudimg-amd64-disk-kvm.img +qemu-img convert jammy-server-cloudimg-amd64-disk-kvm.img jammy-server-cloudimg-amd64-disk-kvm.raw +2. Set up a loop device with RAW image +losetup -b 4096 -f jammy-server-cloudimg-amd64-disk-kvm.raw +3. Get loop device number by `losetup -a` command +4. Start the virtual machine +qemu-system-x86_64 -enable-kvm -drive file=/dev/loopX,format=raw,cache=none --nographic + +[Where problems could occur] +The patch addressed the issue of misusing the memory offset as the block size. +This problem only occurred when the cache option was set to "none" and the Linux kernel being used had the commit b1a000d3b8ec. +However, it is worth noting that the patch also worked effectively with older kernels. + +[Other Info] \ No newline at end of file |