RE: [PATCH v3 11/11] scsi: storvsc: Support PAGE_SIZE larger than 4K

[Michael Kelley <mikelley@microsoft.com>]

From: Boqun Feng <boqun.feng@gmail.com> Sent: Thursday, September 10, 2020 7:35 AM
> 
> 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 | 54 +++++++++++++++++++++++++++++++++-----
>  1 file changed, 47 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c
> index 8f5f5dc863a4..119b76ca24a1 100644
> --- a/drivers/scsi/storvsc_drv.c
> +++ b/drivers/scsi/storvsc_drv.c
> @@ -1739,23 +1739,63 @@ 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 hvpgoff = 0;
> +		unsigned long hvpg_offset = sgl->offset & ~HV_HYP_PAGE_MASK;

This is a minor nit.  The above expression uses sgl->offset.  Code below uses
sgl[0].offset.  They're the same but the inconsistency sticks out a bit.

> +		unsigned int hvpg_count = HVPFN_UP(hvpg_offset + length);
> +		u64 hvpfn;
> 
> -			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;

Another nit.  The right hand side of the above assignment is already calculated as
hvpg_offset.

Nits aside,

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

> +		hvpgoff = 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)));
> -			cur_sgl = sg_next(cur_sgl);
> +		for (i = 0; i < hvpg_count; i++) {
> +			/*
> +			 * '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 ---------------------------+
> +			 */
> +			unsigned int hvpgoff_in_page =
> +				(i + hvpgoff) % NR_HV_HYP_PAGES_IN_PAGE;
> +
> +			/*
> +			 * 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.
> +			 */
> +			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;
>  		}
>  	}
> 
> --
> 2.28.0