Commit 1d3e0980 authored by Saurabh Sengar's avatar Saurabh Sengar Committed by Martin K. Petersen
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scsi: storvsc: Correct reporting of Hyper-V I/O size limits 

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 3d9c3dcc ("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: 3d9c3dcc ("scsi: storvsc: Enable scatter list entry lengths > 4Kbytes")
Reviewed-by: default avatarMichael Kelley <mikelley@microsoft.com>
Signed-off-by: default avatarSaurabh Sengar <ssengar@linux.microsoft.com>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent 2acd76e7

drivers/scsi/storvsc_drv.c

+22 −5
Original line number Diff line number Diff line
@@ -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.

	 */

	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 = (stor_device->max_transfer_bytes >> PAGE_SHIFT);

	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.