scsi: storvsc: Enable scatterlist entry lengths > 4Kbytes

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).

Link: https://lore.kernel.org/r/1614120294-1930-1-git-send-email-mikelley@microsoft.com
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index dfe005c..e6718a7 100644 (file)
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -1692,9 +1692,8 @@ 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;
@@ -1773,8 +1772,8 @@ 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;
 
@@ -1787,51 +1786,34 @@ 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++;
                }
        }
 
@@ -1865,8 +1847,6 @@ static struct scsi_host_template scsi_driver = {
        .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 f1d74dc..7be8c5f 100644 (file)
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1726,6 +1726,7 @@ 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 */