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Subject[PATCH v2 1/1] scsi: storvsc: Enable scatterlist entry lengths > 4Kbytes
Date
storvsc currently sets .dma_boundary to limit scatterlist entries
to 4 Kbytes, which is less efficient with huge pages that offer
large chunks of contiguous physical memory. Improve the algorithm
for creating the Hyper-V guest physical address PFN array so
that scatterlist entries with lengths > 4Kbytes are handled.
As a result, remove the .dma_boundary setting.

The improved algorithm also adds support for scatterlist
entries with offsets >= 4Kbytes, which is supported by many
other SCSI low-level drivers. And it retains support for
architectures where possibly PAGE_SIZE != HV_HYP_PAGE_SIZE
(such as ARM64).

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
---

Changes in v2:
* Add HVPFN_DOWN() macro and use it instead of open coding
[Vitaly Kuznetsov]
* Change loop that fills pfn array and its initialization
[Vitaly Kuznetsov]
* Use offset_in_hvpage() instead of open coding


drivers/scsi/storvsc_drv.c | 66 ++++++++++++++++------------------------------
include/linux/hyperv.h | 1 +
2 files changed, 24 insertions(+), 43 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 2e4fa77..5ba3145 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1678,9 +1678,8 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
struct storvsc_cmd_request *cmd_request = scsi_cmd_priv(scmnd);
int i;
struct scatterlist *sgl;
- unsigned int sg_count = 0;
+ unsigned int sg_count;
struct vmscsi_request *vm_srb;
- struct scatterlist *cur_sgl;
struct vmbus_packet_mpb_array *payload;
u32 payload_sz;
u32 length;
@@ -1759,8 +1758,8 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
payload_sz = sizeof(cmd_request->mpb);

if (sg_count) {
- unsigned int hvpgoff = 0;
- unsigned long offset_in_hvpg = sgl->offset & ~HV_HYP_PAGE_MASK;
+ unsigned int hvpgoff, hvpfns_to_add;
+ unsigned long offset_in_hvpg = offset_in_hvpage(sgl->offset);
unsigned int hvpg_count = HVPFN_UP(offset_in_hvpg + length);
u64 hvpfn;

@@ -1773,51 +1772,34 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
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.
- * Besides, payload->range.offset should be the offset in one
- * HV_HYP_PAGE.
- */
payload->range.len = length;
payload->range.offset = offset_in_hvpg;
- hvpgoff = sgl->offset >> HV_HYP_PAGE_SHIFT;

- cur_sgl = sgl;
- for (i = 0; i < hvpg_count; i++) {
+
+ for (i = 0; sgl != NULL; sgl = sg_next(sgl)) {
/*
- * 'i' is the index of hv pages in the payload and
- * 'hvpgoff' is the offset (in hv pages) of the first
- * hv page in the the first page. The relationship
- * between the sum of 'i' and 'hvpgoff' and the offset
- * (in hv pages) in a payload page ('hvpgoff_in_page')
- * is as follow:
- *
- * |------------------ PAGE -------------------|
- * | NR_HV_HYP_PAGES_IN_PAGE hvpgs in total |
- * |hvpg|hvpg| ... |hvpg|... |hvpg|
- * ^ ^ ^ ^
- * +-hvpgoff-+ +-hvpgoff_in_page-+
- * ^ |
- * +--------------------- i ---------------------------+
+ * Init values for the current sgl entry. hvpgoff
+ * and hvpfns_to_add are in units of Hyper-V size
+ * pages. Handling the PAGE_SIZE != HV_HYP_PAGE_SIZE
+ * case also handles values of sgl->offset that are
+ * larger than PAGE_SIZE. Such offsets are handled
+ * even on other than the first sgl entry, provided
+ * they are a multiple of PAGE_SIZE.
*/
- unsigned int hvpgoff_in_page =
- (i + hvpgoff) % NR_HV_HYP_PAGES_IN_PAGE;
+ hvpgoff = HVPFN_DOWN(sgl->offset);
+ hvpfn = page_to_hvpfn(sg_page(sgl)) + hvpgoff;
+ hvpfns_to_add = HVPFN_UP(sgl->offset + sgl->length) -
+ hvpgoff;

/*
- * Two cases that we need to fetch a page:
- * 1) i == 0, the first step or
- * 2) hvpgoff_in_page == 0, when we reach the boundary
- * of a page.
+ * Fill the next portion of the PFN array with
+ * sequential Hyper-V PFNs for the continguous physical
+ * memory described by the sgl entry. The end of the
+ * last sgl should be reached at the same time that
+ * the PFN array is filled.
*/
- if (hvpgoff_in_page == 0 || i == 0) {
- hvpfn = page_to_hvpfn(sg_page(cur_sgl));
- cur_sgl = sg_next(cur_sgl);
- }
-
- payload->range.pfn_array[i] = hvpfn + hvpgoff_in_page;
+ while (hvpfns_to_add--)
+ payload->range.pfn_array[i++] = hvpfn++;
}
}

@@ -1851,8 +1833,6 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
.slave_configure = storvsc_device_configure,
.cmd_per_lun = 2048,
.this_id = -1,
- /* Make sure we dont get a sg segment crosses a page boundary */
- .dma_boundary = PAGE_SIZE-1,
/* Ensure there are no gaps in presented sgls */
.virt_boundary_mask = PAGE_SIZE-1,
.no_write_same = 1,
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 5ddb479..a1eed76 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1717,6 +1717,7 @@ static inline unsigned long virt_to_hvpfn(void *addr)
#define NR_HV_HYP_PAGES_IN_PAGE (PAGE_SIZE / HV_HYP_PAGE_SIZE)
#define offset_in_hvpage(ptr) ((unsigned long)(ptr) & ~HV_HYP_PAGE_MASK)
#define HVPFN_UP(x) (((x) + HV_HYP_PAGE_SIZE-1) >> HV_HYP_PAGE_SHIFT)
+#define HVPFN_DOWN(x) ((x) >> HV_HYP_PAGE_SHIFT)
#define page_to_hvpfn(page) (page_to_pfn(page) * NR_HV_HYP_PAGES_IN_PAGE)

#endif /* _HYPERV_H */
--
1.8.3.1
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