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scsi: storvsc: Correct reporting of Hyper-V I/O size limits

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Current code is based on the idea that the max number of SGL entries
also determines the max size of an I/O request.  While this idea was
true in older versions of the storvsc driver when SGL entry length
was limited to 4 Kbytes, commit 3d9c3dcc58 ("scsi: storvsc: Enable
scatterlist entry lengths > 4Kbytes") removed that limitation. It's
now theoretically possible for the block layer to send requests that
exceed the maximum size supported by Hyper-V. This problem doesn't
currently happen in practice because the block layer defaults to a
512 Kbyte maximum, while Hyper-V in Azure supports 2 Mbyte I/O sizes.
But some future configuration of Hyper-V could have a smaller max I/O
size, and the block layer could exceed that max.

Fix this by correctly setting max_sectors as well as sg_tablesize to
reflect the maximum I/O size that Hyper-V reports. While allowing
I/O sizes larger than the block layer default of 512 Kbytes doesn’t
provide any noticeable performance benefit in the tests we ran, it's
still appropriate to report the correct underlying Hyper-V capabilities
to the Linux block layer.

Also tweak the virt_boundary_mask to reflect that the required
alignment derives from Hyper-V communication using a 4 Kbyte page size,
and not on the guest page size, which might be bigger (eg. ARM64).

Link: https://lore.kernel.org/r/1655190355-28722-1-git-send-email-ssengar@linux.microsoft.com
Fixes: 3d9c3dcc58 ("scsi: storvsc: Enable scatter list entry lengths > 4Kbytes")
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Saurabh Sengar 2022-06-14 00:05:55 -07:00 committed by Martin K. Petersen
parent 2acd76e7b8
commit 1d3e098078
1 changed files with 22 additions and 5 deletions
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27
drivers/scsi/storvsc_drv.c
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@ -1844,7 +1844,7 @@ static struct scsi_host_template scsi_driver = {
.cmd_per_lun = 2048,
.this_id = -1,
/* Ensure there are no gaps in presented sgls */
.virt_boundary_mask = PAGE_SIZE-1,
.virt_boundary_mask = HV_HYP_PAGE_SIZE - 1,
.no_write_same = 1,
.track_queue_depth = 1,
.change_queue_depth = storvsc_change_queue_depth,
@ -1895,6 +1895,7 @@ static int storvsc_probe(struct hv_device *device,
int target = 0;
struct storvsc_device *stor_device;
int max_sub_channels = 0;
u32 max_xfer_bytes;
/*
* We support sub-channels for storage on SCSI and FC controllers.
@ -1968,12 +1969,28 @@ static int storvsc_probe(struct hv_device *device,
}
/* max cmd length */
host->max_cmd_len = STORVSC_MAX_CMD_LEN;
/*
* set the table size based on the info we got
* from the host.
* Any reasonable Hyper-V configuration should provide
* max_transfer_bytes value aligning to HV_HYP_PAGE_SIZE,
* protecting it from any weird value.
*/
host->sg_tablesize = (stor_device->max_transfer_bytes >> PAGE_SHIFT);
max_xfer_bytes = round_down(stor_device->max_transfer_bytes, HV_HYP_PAGE_SIZE);
/* max_hw_sectors_kb */
host->max_sectors = max_xfer_bytes >> 9;
/*
* There are 2 requirements for Hyper-V storvsc sgl segments,
* based on which the below calculation for max segments is
* done:
*
* 1. Except for the first and last sgl segment, all sgl segments
* should be align to HV_HYP_PAGE_SIZE, that also means the
* maximum number of segments in a sgl can be calculated by
* dividing the total max transfer length by HV_HYP_PAGE_SIZE.
*
* 2. Except for the first and last, each entry in the SGL must
* have an offset that is a multiple of HV_HYP_PAGE_SIZE.
*/
host->sg_tablesize = (max_xfer_bytes >> HV_HYP_PAGE_SHIFT) + 1;
/*
* For non-IDE disks, the host supports multiple channels.
* Set the number of HW queues we are supporting.