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[PATCH] storvsc: get rid of homegrown copy_{to,from}_bounce_buffer()

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  [PATCH] storvsc: get rid of homegrown copy_{to,from}_bounce_buffer() Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-09-22 18:30 +0200
    Re: [PATCH] storvsc: get rid of homegrown  copy_{to,from}_bounce_buffer() Christoph Hellwig <hch@infradead.org> - 2015-09-23 00:00 +0200
      Re: [PATCH] storvsc: get rid of homegrown copy_{to,from}_bounce_buffer() Vitaly Kuznetsov <vkuznets@redhat.com> - 2015-09-23 13:40 +0200

#1230444 — [PATCH] storvsc: get rid of homegrown copy_{to,from}_bounce_buffer()

Storvsc driver needs to ensure there are no 'holes' in the presented
sg list (all segments in the middle of the list need to be of PAGE_SIZE).
When a hole is detected storvsc driver creates a 'bounce sgl' without
holes and copies data over with its own copy_{to,from}_bounce_buffer()
functions. Scsi layer already has scsi_sg_copy_{to,from}_buffer()
functions to linearize a list, the only difference is that already
existent functions create a flat buffer instead of a new list but we can
cope.

Reported-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 drivers/scsi/storvsc_drv.c | 281 ++++++---------------------------------------
 1 file changed, 36 insertions(+), 245 deletions(-)

diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
index 40c43ae..31e8c67 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -393,8 +393,8 @@ static void storvsc_on_channel_callback(void *context);
 struct storvsc_cmd_request {
 	struct scsi_cmnd *cmd;
 
-	unsigned int bounce_sgl_count;
-	struct scatterlist *bounce_sgl;
+	unsigned int bounce_len;
+	void *bounce_buf;
 
 	struct hv_device *device;
 
@@ -586,21 +586,6 @@ get_in_err:
 
 }
 
-static void destroy_bounce_buffer(struct scatterlist *sgl,
-				  unsigned int sg_count)
-{
-	int i;
-	struct page *page_buf;
-
-	for (i = 0; i < sg_count; i++) {
-		page_buf = sg_page((&sgl[i]));
-		if (page_buf != NULL)
-			__free_page(page_buf);
-	}
-
-	kfree(sgl);
-}
-
 static int do_bounce_buffer(struct scatterlist *sgl, unsigned int sg_count)
 {
 	int i;
@@ -628,199 +613,6 @@ static int do_bounce_buffer(struct scatterlist *sgl, unsigned int sg_count)
 	return -1;
 }
 
-static struct scatterlist *create_bounce_buffer(struct scatterlist *sgl,
-						unsigned int sg_count,
-						unsigned int len,
-						int write)
-{
-	int i;
-	int num_pages;
-	struct scatterlist *bounce_sgl;
-	struct page *page_buf;
-	unsigned int buf_len = ((write == WRITE_TYPE) ? 0 : PAGE_SIZE);
-
-	num_pages = ALIGN(len, PAGE_SIZE) >> PAGE_SHIFT;
-
-	bounce_sgl = kcalloc(num_pages, sizeof(struct scatterlist), GFP_ATOMIC);
-	if (!bounce_sgl)
-		return NULL;
-
-	sg_init_table(bounce_sgl, num_pages);
-	for (i = 0; i < num_pages; i++) {
-		page_buf = alloc_page(GFP_ATOMIC);
-		if (!page_buf)
-			goto cleanup;
-		sg_set_page(&bounce_sgl[i], page_buf, buf_len, 0);
-	}
-
-	return bounce_sgl;
-
-cleanup:
-	destroy_bounce_buffer(bounce_sgl, num_pages);
-	return NULL;
-}
-
-/* Assume the original sgl has enough room */
-static unsigned int copy_from_bounce_buffer(struct scatterlist *orig_sgl,
-					    struct scatterlist *bounce_sgl,
-					    unsigned int orig_sgl_count,
-					    unsigned int bounce_sgl_count)
-{
-	int i;
-	int j = 0;
-	unsigned long src, dest;
-	unsigned int srclen, destlen, copylen;
-	unsigned int total_copied = 0;
-	unsigned long bounce_addr = 0;
-	unsigned long dest_addr = 0;
-	unsigned long flags;
-	struct scatterlist *cur_dest_sgl;
-	struct scatterlist *cur_src_sgl;
-
-	local_irq_save(flags);
-	cur_dest_sgl = orig_sgl;
-	cur_src_sgl = bounce_sgl;
-	for (i = 0; i < orig_sgl_count; i++) {
-		dest_addr = (unsigned long)
-				kmap_atomic(sg_page(cur_dest_sgl)) +
-				cur_dest_sgl->offset;
-		dest = dest_addr;
-		destlen = cur_dest_sgl->length;
-
-		if (bounce_addr == 0)
-			bounce_addr = (unsigned long)kmap_atomic(
-							sg_page(cur_src_sgl));
-
-		while (destlen) {
-			src = bounce_addr + cur_src_sgl->offset;
-			srclen = cur_src_sgl->length - cur_src_sgl->offset;
-
-			copylen = min(srclen, destlen);
-			memcpy((void *)dest, (void *)src, copylen);
-
-			total_copied += copylen;
-			cur_src_sgl->offset += copylen;
-			destlen -= copylen;
-			dest += copylen;
-
-			if (cur_src_sgl->offset == cur_src_sgl->length) {
-				/* full */
-				kunmap_atomic((void *)bounce_addr);
-				j++;
-
-				/*
-				 * It is possible that the number of elements
-				 * in the bounce buffer may not be equal to
-				 * the number of elements in the original
-				 * scatter list. Handle this correctly.
-				 */
-
-				if (j == bounce_sgl_count) {
-					/*
-					 * We are done; cleanup and return.
-					 */
-					kunmap_atomic((void *)(dest_addr -
-						cur_dest_sgl->offset));
-					local_irq_restore(flags);
-					return total_copied;
-				}
-
-				/* if we need to use another bounce buffer */
-				if (destlen || i != orig_sgl_count - 1) {
-					cur_src_sgl = sg_next(cur_src_sgl);
-					bounce_addr = (unsigned long)
-							kmap_atomic(
-							sg_page(cur_src_sgl));
-				}
-			} else if (destlen == 0 && i == orig_sgl_count - 1) {
-				/* unmap the last bounce that is < PAGE_SIZE */
-				kunmap_atomic((void *)bounce_addr);
-			}
-		}
-
-		kunmap_atomic((void *)(dest_addr - cur_dest_sgl->offset));
-		cur_dest_sgl = sg_next(cur_dest_sgl);
-	}
-
-	local_irq_restore(flags);
-
-	return total_copied;
-}
-
-/* Assume the bounce_sgl has enough room ie using the create_bounce_buffer() */
-static unsigned int copy_to_bounce_buffer(struct scatterlist *orig_sgl,
-					  struct scatterlist *bounce_sgl,
-					  unsigned int orig_sgl_count)
-{
-	int i;
-	int j = 0;
-	unsigned long src, dest;
-	unsigned int srclen, destlen, copylen;
-	unsigned int total_copied = 0;
-	unsigned long bounce_addr = 0;
-	unsigned long src_addr = 0;
-	unsigned long flags;
-	struct scatterlist *cur_src_sgl;
-	struct scatterlist *cur_dest_sgl;
-
-	local_irq_save(flags);
-
-	cur_src_sgl = orig_sgl;
-	cur_dest_sgl = bounce_sgl;
-
-	for (i = 0; i < orig_sgl_count; i++) {
-		src_addr = (unsigned long)
-				kmap_atomic(sg_page(cur_src_sgl)) +
-				cur_src_sgl->offset;
-		src = src_addr;
-		srclen = cur_src_sgl->length;
-
-		if (bounce_addr == 0)
-			bounce_addr = (unsigned long)
-					kmap_atomic(sg_page(cur_dest_sgl));
-
-		while (srclen) {
-			/* assume bounce offset always == 0 */
-			dest = bounce_addr + cur_dest_sgl->length;
-			destlen = PAGE_SIZE - cur_dest_sgl->length;
-
-			copylen = min(srclen, destlen);
-			memcpy((void *)dest, (void *)src, copylen);
-
-			total_copied += copylen;
-			cur_dest_sgl->length += copylen;
-			srclen -= copylen;
-			src += copylen;
-
-			if (cur_dest_sgl->length == PAGE_SIZE) {
-				/* full..move to next entry */
-				kunmap_atomic((void *)bounce_addr);
-				bounce_addr = 0;
-				j++;
-			}
-
-			/* if we need to use another bounce buffer */
-			if (srclen && bounce_addr == 0) {
-				cur_dest_sgl = sg_next(cur_dest_sgl);
-				bounce_addr = (unsigned long)
-						kmap_atomic(
-						sg_page(cur_dest_sgl));
-			}
-
-		}
-
-		kunmap_atomic((void *)(src_addr - cur_src_sgl->offset));
-		cur_src_sgl = sg_next(cur_src_sgl);
-	}
-
-	if (bounce_addr)
-		kunmap_atomic((void *)bounce_addr);
-
-	local_irq_restore(flags);
-
-	return total_copied;
-}
-
 static void handle_sc_creation(struct vmbus_channel *new_sc)
 {
 	struct hv_device *device = new_sc->primary_channel->device_obj;
@@ -1171,14 +963,11 @@ static void storvsc_command_completion(struct storvsc_cmd_request *cmd_request)
 	host = stor_dev->host;
 
 	vm_srb = &cmd_request->vstor_packet.vm_srb;
-	if (cmd_request->bounce_sgl_count) {
+	if (cmd_request->bounce_len) {
 		if (vm_srb->data_in == READ_TYPE)
-			copy_from_bounce_buffer(scsi_sglist(scmnd),
-					cmd_request->bounce_sgl,
-					scsi_sg_count(scmnd),
-					cmd_request->bounce_sgl_count);
-		destroy_bounce_buffer(cmd_request->bounce_sgl,
-					cmd_request->bounce_sgl_count);
+			scsi_sg_copy_from_buffer(scmnd, cmd_request->bounce_buf,
+						 cmd_request->bounce_len);
+		kfree(cmd_request->bounce_buf);
 	}
 
 	scmnd->result = vm_srb->scsi_status;
@@ -1694,48 +1483,51 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
 	if (sg_count) {
 		/* check if we need to bounce the sgl */
 		if (do_bounce_buffer(sgl, scsi_sg_count(scmnd)) != -1) {
-			cmd_request->bounce_sgl =
-				create_bounce_buffer(sgl, sg_count,
-						     length,
-						     vm_srb->data_in);
-			if (!cmd_request->bounce_sgl)
+			cmd_request->bounce_buf = kmalloc(length, GFP_ATOMIC);
+			if (!cmd_request->bounce_buf)
 				return SCSI_MLQUEUE_HOST_BUSY;
 
-			cmd_request->bounce_sgl_count =
-				ALIGN(length, PAGE_SIZE) >> PAGE_SHIFT;
+			cmd_request->bounce_len = length;
 
 			if (vm_srb->data_in == WRITE_TYPE)
-				copy_to_bounce_buffer(sgl,
-					cmd_request->bounce_sgl, sg_count);
+				scsi_sg_copy_to_buffer(scmnd,
+						       cmd_request->bounce_buf,
+						       cmd_request->bounce_len);
 
-			sgl = cmd_request->bounce_sgl;
-			sg_count = cmd_request->bounce_sgl_count;
+			sg_count = ALIGN(length, PAGE_SIZE) >> PAGE_SHIFT;
 		}
 
-
 		if (sg_count > MAX_PAGE_BUFFER_COUNT) {
-
 			payload_sz = (sg_count * sizeof(void *) +
 				      sizeof(struct vmbus_packet_mpb_array));
 			payload = kmalloc(payload_sz, GFP_ATOMIC);
 			if (!payload) {
-				if (cmd_request->bounce_sgl_count)
-					destroy_bounce_buffer(
-					cmd_request->bounce_sgl,
-					cmd_request->bounce_sgl_count);
-
-					return SCSI_MLQUEUE_DEVICE_BUSY;
+				if (cmd_request->bounce_len)
+					kfree(cmd_request->bounce_buf);
+				return SCSI_MLQUEUE_DEVICE_BUSY;
 			}
 		}
 
 		payload->range.len = length;
-		payload->range.offset = sgl[0].offset;
 
-		cur_sgl = sgl;
-		for (i = 0; i < sg_count; i++) {
-			payload->range.pfn_array[i] =
-				page_to_pfn(sg_page((cur_sgl)));
-			cur_sgl = sg_next(cur_sgl);
+		if (!cmd_request->bounce_len) {
+			payload->range.offset = sgl[0].offset;
+
+			cur_sgl = sgl;
+			for (i = 0; i < sg_count; i++) {
+				payload->range.pfn_array[i] =
+					page_to_pfn(sg_page((cur_sgl)));
+				cur_sgl = sg_next(cur_sgl);
+			}
+		} else {
+			payload->range.offset =	(unsigned long)
+				cmd_request->bounce_buf & ~PAGE_MASK;
+
+			for (i = 0; i < sg_count; i++)
+				payload->range.pfn_array[i] =
+					virt_to_phys(cmd_request->bounce_buf +
+						     i * PAGE_SIZE)
+					>> PAGE_SHIFT;
 		}
 
 	} else if (scsi_sglist(scmnd)) {
@@ -1755,9 +1547,8 @@ static int storvsc_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scmnd)
 	if (ret == -EAGAIN) {
 		/* no more space */
 
-		if (cmd_request->bounce_sgl_count)
-			destroy_bounce_buffer(cmd_request->bounce_sgl,
-					cmd_request->bounce_sgl_count);
+		if (cmd_request->bounce_len)
+			kfree(cmd_request->bounce_buf);
 
 		return SCSI_MLQUEUE_DEVICE_BUSY;
 	}
-- 
2.4.3

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#1230993 — Re: [PATCH] storvsc: get rid of homegrown copy_{to,from}_bounce_buffer()

On Tue, Sep 22, 2015 at 06:27:50PM +0200, Vitaly Kuznetsov wrote:
> Storvsc driver needs to ensure there are no 'holes' in the presented
> sg list (all segments in the middle of the list need to be of PAGE_SIZE).

I think it should instead set a virt_boundary.  That's what we added for
the NVMe driver which has the same requirements, and Sagi recently also
switched iSER to it after we ensured that flag is handled correctly by
the SG_IO ioctl.
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#1231371

Christoph Hellwig <hch@infradead.org> writes:

> On Tue, Sep 22, 2015 at 06:27:50PM +0200, Vitaly Kuznetsov wrote:
>> Storvsc driver needs to ensure there are no 'holes' in the presented
>> sg list (all segments in the middle of the list need to be of PAGE_SIZE).
>
> I think it should instead set a virt_boundary.  That's what we added for
> the NVMe driver which has the same requirements, and Sagi recently also
> switched iSER to it after we ensured that flag is handled correctly by
> the SG_IO ioctl.

Wow,

I checked and blk_queue_virt_boundary(sdevice->request_queue, PAGE_SIZE
- 1) seems to be solving the issue completely, no bounce buffer
required. I'll test more and send v2 with removing the rest.

-- 
  Vitaly
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