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. Stefan
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