On Thu, 24 Sep 2020, Sudhakar Panneerselvam wrote: > Hi Mikulas, > > > > Windows Guest <--> Vhost-Scsi <--> LIO(scsi/target/blockio) <--> dm-crypt > > <--> iSCSI block device > > > > > > One real example out of my debugging: Windows sends a I/O request with > > > 6656 bytes to vhost-scsi interface. Vhost-scsi uses translate_desc() in > > > drivers/vhost/vhost.c to convert windows user space memory buffers to > > > kernel iovecs. Vhost-scsi then converts the iovecs to sg entries in > > > vhost_scsi_mapal() which is then handed over to "target" subsystem and > > > eventually submitted to dm-crypt. This 6656 bytes IO has got 3 segments, > > > first segment had 1584, second 4096 and the last had 976 bytes. Dm-crypt > > > rejects the I/O after seeing the first segment length 1584 which is not > > > a 512 byte multiple. > > > > > > Let me know if there are further questions. > > > > > > Thanks > > > Sudhakar > > > > Hi > > > > I think it should be fixed in vhost-scsi. > > In the above example of 6656 bytes I/O, windows allocates 6656 bytes > virtually contiguous I/O. This IO, when it lands in the kernel, > translates to 3 physically discontiguous pages, that's why > translate_desc() had to create 3 iovecs to handle this I/O. I don't > understand how vhost-scsi could have solved this issue. By copying it to a temporary aligned buffer and issuing I/O on this buffer. > Only other > possibility I see is to have windows fix it by always sending 512 byte > aligned buffer lengths, but going with my earlier point that every other > component in the Linux IO path handles this case well except for > dm-crypt, so it make more sense to fix it in dm-crypt. > > Thanks > Sudhakar Are you sure that the problem is only with dm-crypt? You haven't tried all the existing block device drivers, have you? Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
