[RFC v2 11/11] scsi: storvsc: Support PAGE_SIZE larger than 4K

[Boqun Feng <boqun.feng@gmail.com>]

Hyper-V always use 4k page size (HV_HYP_PAGE_SIZE), so when
communicating with Hyper-V, a guest should always use HV_HYP_PAGE_SIZE
as the unit for page related data. For storvsc, the data is
vmbus_packet_mpb_array. And since in scsi_cmnd, sglist of pages (in unit
of PAGE_SIZE) is used, we need convert pages in the sglist of scsi_cmnd
into Hyper-V pages in vmbus_packet_mpb_array.

This patch does the conversion by dividing pages in sglist into Hyper-V
pages, offset and indexes in vmbus_packet_mpb_array are recalculated
accordingly.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 drivers/scsi/storvsc_drv.c | 60 ++++++++++++++++++++++++++++++++++----
 1 file changed, 54 insertions(+), 6 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 8f5f5dc863a4..3f6610717d4e 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1739,23 +1739,71 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
 	payload_sz = sizeof(cmd_request->mpb);
 
 	if (sg_count) {
-		if (sg_count > MAX_PAGE_BUFFER_COUNT) {
+		unsigned int hvpg_idx = 0;
+		unsigned int j = 0;
+		unsigned long hvpg_offset = sgl->offset & ~HV_HYP_PAGE_MASK;
+		unsigned int hvpg_count = HVPFN_UP(hvpg_offset + length);
 
-			payload_sz = (sg_count * sizeof(u64) +
+		if (hvpg_count > MAX_PAGE_BUFFER_COUNT) {
+
+			payload_sz = (hvpg_count * sizeof(u64) +
 				      sizeof(struct vmbus_packet_mpb_array));
 			payload = kzalloc(payload_sz, GFP_ATOMIC);
 			if (!payload)
 				return SCSI_MLQUEUE_DEVICE_BUSY;
 		}
 
+		/*
+		 * sgl is a list of PAGEs, and payload->range.pfn_array
+		 * expects the page number in the unit of HV_HYP_PAGE_SIZE (the
+		 * page size that Hyper-V uses, so here we need to divide PAGEs
+		 * into HV_HYP_PAGE in case that PAGE_SIZE > HV_HYP_PAGE_SIZE.
+		 */
 		payload->range.len = length;
-		payload->range.offset = sgl[0].offset;
+		payload->range.offset = sgl[0].offset & ~HV_HYP_PAGE_MASK;
+		hvpg_idx = sgl[0].offset >> HV_HYP_PAGE_SHIFT;
 
 		cur_sgl = sgl;
-		for (i = 0; i < sg_count; i++) {
-			payload->range.pfn_array[i] =
-				page_to_pfn(sg_page((cur_sgl)));
+		for (i = 0, j = 0; i < sg_count; i++) {
+			/*
+			 * "PAGE_SIZE / HV_HYP_PAGE_SIZE - hvpg_idx" is the #
+			 * of HV_HYP_PAGEs in the current PAGE.
+			 *
+			 * "hvpg_count - j" is the # of unhandled HV_HYP_PAGEs.
+			 *
+			 * As shown in the following, the minimal of both is
+			 * the # of HV_HYP_PAGEs, we need to handle in this
+			 * PAGE.
+			 *
+			 * |------------------ PAGE ----------------------|
+			 * |   PAGE_SIZE / HV_HYP_PAGE_SIZE in total      |
+			 * |hvpg|hvpg| ...                 |hvpg|... |hvpg|
+			 *           ^                     ^
+			 *         hvpg_idx                |
+			 *           ^                     |
+			 *           +---(hvpg_count - j)--+
+			 *
+			 * or
+			 *
+			 * |------------------ PAGE ----------------------|
+			 * |   PAGE_SIZE / HV_HYP_PAGE_SIZE in total      |
+			 * |hvpg|hvpg| ...                 |hvpg|... |hvpg|
+			 *           ^                                           ^
+			 *         hvpg_idx                                      |
+			 *           ^                                           |
+			 *           +---(hvpg_count - j)------------------------+
+			 */
+			unsigned int nr_hvpg = min((unsigned int)(PAGE_SIZE / HV_HYP_PAGE_SIZE) - hvpg_idx,
+						   hvpg_count - j);
+			unsigned int k;
+
+			for (k = 0; k < nr_hvpg; k++) {
+				payload->range.pfn_array[j] =
+					page_to_hvpfn(sg_page((cur_sgl))) + hvpg_idx + k;
+				j++;
+			}
 			cur_sgl = sg_next(cur_sgl);
+			hvpg_idx = 0;
 		}
 	}
 
-- 
2.28.0