On 7/12/23 9:26 AM, Stefan Hajnoczi wrote: > On Tue, Jul 11, 2023 at 04:01:22PM -0500, Mike Christie wrote: >> On 7/11/23 1:34 PM, Stefan Hajnoczi wrote: >>> On Sun, Jul 09, 2023 at 03:28:57PM -0500, Mike Christie wrote: >>>> The following patches were made over Linus's tree and fix an issue >>>> where windows guests will send iovecs with offset/lengths that result >>>> in IOs that are not aligned to 512. The LIO layer will then send them >>>> to Linux's FS/block layer but it requires 512 byte alignment, so >>>> depending on the FS/block driver being used we will get IO errors or >>>> hung IO. >>>> >>>> The following patches have vhost-scsi detect when windows sends these >>>> IOs and copy them to a bounce buffer. It then does some cleanup in >>>> the related code. >>> >>> Hang on, virtio-scsi is a SCSI HBA and READs/WRITEs submitted must >>> follow the usual constraints on SCSI block limits. Would Windows send >>> mis-aligned I/O to a non-virtio-scsi SCSI HBA? >> >> It's like linux where you can config settings like that. >> >>>> Are you sure this is not a bug in the Windows guest driver where block >>> limits are being misconfigured? >> >> From what our windows dev told us the guest drivers like here: >> >> https://github.com/virtio-win >> >> don't set the windows AlignmentMask to 512. They tried that and it >> resulted in windows crash dump crashing because it doesn't like the >> hard alignment requirement. >> >> We thought other apps would have trouble as well, so we tried to add >> bounce buffer support to the windows driver, but I think people thought >> it was going to be uglier than this patch and in the normal alignment >> case might also affect performance. There was some windows driver/layering >> and buffer/cmd details that I don't fully understand and took their word >> for because I don't know a lot about windows. >> >> In the end we still have to add checks to vhost-scsi to protect against >> bad drivers, so we thought we might as well just add bounce buffer support >> to vhost-scsi. > > CCing virtio-win developers so they can confirm how the vioscsi driver > is supposed to handle request alignment. > > My expectation is that the virtio-scsi device will fail mis-aligned I/O > requests. I don't think you can just change the driver's behavior to fail now, because apps send mis-aligned IO and its working as long as they have less than 256 bio vecs. We see mis-aligned IOs during boot and also from random non window's apps. If we just start to fail then it would be a regression when the app no longer works or the OS fails to start up.
