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From: Jason Gunthorpe <jgg@nvidia.com>
To: Logan Gunthorpe <logang@deltatee.com>
Cc: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-mm@kvack.org, iommu@lists.linux-foundation.org,
	"Stephen Bates" <sbates@raithlin.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Christian König" <christian.koenig@amd.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Don Dutile" <ddutile@redhat.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	"Jakowski Andrzej" <andrzej.jakowski@intel.com>,
	"Minturn Dave B" <dave.b.minturn@intel.com>,
	"Jason Ekstrand" <jason@jlekstrand.net>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Xiong Jianxin" <jianxin.xiong@intel.com>,
	"Bjorn Helgaas" <helgaas@kernel.org>,
	"Ira Weiny" <ira.weiny@intel.com>,
	"Robin Murphy" <robin.murphy@arm.com>,
	"Martin Oliveira" <martin.oliveira@eideticom.com>,
	"Chaitanya Kulkarni" <ckulkarnilinux@gmail.com>
Subject: Re: [PATCH v3 4/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations
Date: Wed, 29 Sep 2021 19:46:53 -0300	[thread overview]
Message-ID: <20210929224653.GZ964074@nvidia.com> (raw)
In-Reply-To: <91469404-fd20-effa-2e01-aa79d9d4b9b5@deltatee.com>

On Wed, Sep 29, 2021 at 03:30:42PM -0600, Logan Gunthorpe wrote:
> 
> 
> 
> On 2021-09-28 4:05 p.m., Jason Gunthorpe wrote:
> > On Thu, Sep 16, 2021 at 05:40:44PM -0600, Logan Gunthorpe wrote:
> > 
> >> +enum pci_p2pdma_map_type
> >> +pci_p2pdma_map_segment(struct pci_p2pdma_map_state *state, struct device *dev,
> >> +		       struct scatterlist *sg)
> >> +{
> >> +	if (state->pgmap != sg_page(sg)->pgmap) {
> >> +		state->pgmap = sg_page(sg)->pgmap;
> > 
> > This has built into it an assumption that every page in the sg element
> > has the same pgmap, but AFAIK nothing enforces this rule? There is no
> > requirement that the HW has pfn gaps between the pgmaps linux decides
> > to create over it.
> 
> No, that's not a correct reading of the code. Every time there is a new
> pagemap, this code calculates the mapping type and bus offset. If a page
> comes along with a different page map,f it recalculates. This just
> reduces the overhead so that the calculation is done only every time a
> page with a different pgmap comes along and not doing it for every
> single page.

Each 'struct scatterlist *sg' refers to a range of contiguous pfns
starting at page_to_pfn(sg_page()) and going for approx sg->length/PAGE_SIZE
pfns long.

sg_page() returns the first page, but nothing says that sg_page()+1
has the same pgmap.

The code in this patch does check the first page of each sg in a
larger sgl.

> > At least sg_alloc_append_table_from_pages() and probably something in
> > the block world should be updated to not combine struct pages with
> > different pgmaps, and this should be documented in scatterlist.*
> > someplace.
> 
> There's no sane place to do this check. The code is designed to support
> mappings with different pgmaps.

All places that generate compound sg's by aggregating multiple pages
need to include this check along side the check for physical
contiguity. There are not that many places but
sg_alloc_append_table_from_pages() is one of them:

@@ -470,7 +470,8 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
 
                /* Merge contiguous pages into the last SG */
                prv_len = sgt_append->prv->length;
-               while (n_pages && page_to_pfn(pages[0]) == paddr) {
+               while (n_pages && page_to_pfn(pages[0]) == paddr &&
+                      sg_page(sgt_append->prv)->pgmap == pages[0]->pgmap) {
                        if (sgt_append->prv->length + PAGE_SIZE > max_segment)
                                break;
                        sgt_append->prv->length += PAGE_SIZE;
@@ -488,7 +489,8 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
        for (i = 1; i < n_pages; i++) {
                seg_len += PAGE_SIZE;
                if (seg_len >= max_segment ||
-                   page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1) {
+                   page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1 ||
+                   pages[i]->pgmap != pages[i - 1]->pgmap) {
                        chunks++;
                        seg_len = 0;
                }
@@ -505,9 +507,10 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append,
                        seg_len += PAGE_SIZE;
                        if (seg_len >= max_segment ||
                            page_to_pfn(pages[j]) !=
-                           page_to_pfn(pages[j - 1]) + 1)
+                                   page_to_pfn(pages[j - 1]) + 1 ||
+                           pages[i]->pgmap != pages[i - 1]->pgmap) {
                                break;
-               }
+                       }
 
                /* Pass how many chunks might be left */
                s = get_next_sg(sgt_append, s, chunks - i + left_pages,



  reply	other threads:[~2021-09-29 22:46 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-16 23:40 [PATCH v3 00/20] Userspace P2PDMA with O_DIRECT NVMe devices Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 01/20] lib/scatterlist: add flag for indicating P2PDMA segments in an SGL Logan Gunthorpe
2021-09-28 18:32   ` Jason Gunthorpe
2021-09-29 21:15     ` Logan Gunthorpe
2021-09-30  4:47   ` Chaitanya Kulkarni
2021-09-30 16:49     ` Logan Gunthorpe
2021-09-30  4:57   ` Chaitanya Kulkarni
2021-09-16 23:40 ` [PATCH v3 02/20] PCI/P2PDMA: attempt to set map_type if it has not been set Logan Gunthorpe
2021-09-27 18:50   ` Bjorn Helgaas
2021-09-16 23:40 ` [PATCH v3 03/20] PCI/P2PDMA: make pci_p2pdma_map_type() non-static Logan Gunthorpe
2021-09-27 18:46   ` Bjorn Helgaas
2021-09-28 18:48   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 04/20] PCI/P2PDMA: introduce helpers for dma_map_sg implementations Logan Gunthorpe
2021-09-27 18:53   ` Bjorn Helgaas
2021-09-27 19:59     ` Logan Gunthorpe
2021-09-28 18:55   ` Jason Gunthorpe
2021-09-29 21:26     ` Logan Gunthorpe
2021-09-28 22:05   ` [PATCH v3 4/20] " Jason Gunthorpe
2021-09-29 21:30     ` Logan Gunthorpe
2021-09-29 22:46       ` Jason Gunthorpe [this message]
2021-09-29 23:00         ` Logan Gunthorpe
2021-09-29 23:40           ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 05/20] dma-mapping: allow EREMOTEIO return code for P2PDMA transfers Logan Gunthorpe
2021-09-28 18:57   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 06/20] dma-direct: support PCI P2PDMA pages in dma-direct map_sg Logan Gunthorpe
2021-09-28 19:08   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 07/20] dma-mapping: add flags to dma_map_ops to indicate PCI P2PDMA support Logan Gunthorpe
2021-09-28 19:11   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 08/20] iommu/dma: support PCI P2PDMA pages in dma-iommu map_sg Logan Gunthorpe
2021-09-28 19:15   ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 09/20] nvme-pci: check DMA ops when indicating support for PCI P2PDMA Logan Gunthorpe
2021-09-30  5:06   ` Chaitanya Kulkarni
2021-09-30 16:51     ` Logan Gunthorpe
2021-09-30 17:19       ` Chaitanya Kulkarni
2021-09-16 23:40 ` [PATCH v3 10/20] nvme-pci: convert to using dma_map_sgtable() Logan Gunthorpe
2021-10-05 22:29   ` Max Gurtovoy
2021-09-16 23:40 ` [PATCH v3 11/20] RDMA/core: introduce ib_dma_pci_p2p_dma_supported() Logan Gunthorpe
2021-09-28 19:17   ` Jason Gunthorpe
2021-10-05 22:31   ` Max Gurtovoy
2021-09-16 23:40 ` [PATCH v3 12/20] RDMA/rw: use dma_map_sgtable() Logan Gunthorpe
2021-09-28 19:43   ` Jason Gunthorpe
2021-09-29 22:56     ` Logan Gunthorpe
2021-10-05 22:40     ` Max Gurtovoy
2021-09-16 23:40 ` [PATCH v3 13/20] PCI/P2PDMA: remove pci_p2pdma_[un]map_sg() Logan Gunthorpe
2021-09-27 18:50   ` Bjorn Helgaas
2021-09-28 19:43   ` Jason Gunthorpe
2021-10-05 22:42   ` Max Gurtovoy
2021-09-16 23:40 ` [PATCH v3 14/20] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages Logan Gunthorpe
2021-09-28 19:47   ` Jason Gunthorpe
2021-09-29 21:34     ` Logan Gunthorpe
2021-09-29 22:48       ` Jason Gunthorpe
2021-09-16 23:40 ` [PATCH v3 15/20] iov_iter: introduce iov_iter_get_pages_[alloc_]flags() Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 16/20] block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get_pages() Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 17/20] block: set FOLL_PCI_P2PDMA in bio_map_user_iov() Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 18/20] mm: use custom page_free for P2PDMA pages Logan Gunthorpe
2021-09-16 23:40 ` [PATCH v3 19/20] PCI/P2PDMA: introduce pci_mmap_p2pmem() Logan Gunthorpe
2021-09-27 18:49   ` Bjorn Helgaas
2021-09-28 19:55   ` Jason Gunthorpe
2021-09-29 21:42     ` Logan Gunthorpe
2021-09-29 23:05       ` Jason Gunthorpe
2021-09-29 23:27         ` Logan Gunthorpe
2021-09-29 23:35           ` Jason Gunthorpe
2021-09-29 23:49             ` Logan Gunthorpe
2021-09-30  0:36               ` Jason Gunthorpe
2021-10-01 13:48                 ` Jason Gunthorpe
2021-10-01 17:01                   ` Logan Gunthorpe
2021-10-01 17:45                     ` Jason Gunthorpe
2021-10-01 20:13                       ` Logan Gunthorpe
2021-10-01 22:14                         ` Jason Gunthorpe
2021-10-01 22:22                           ` Logan Gunthorpe
2021-10-01 22:46                             ` Jason Gunthorpe
2021-10-01 23:27                               ` John Hubbard
2021-10-01 23:34                               ` Logan Gunthorpe
2021-10-04  6:58                       ` Christian König
2021-10-04 13:11                         ` Jason Gunthorpe
2021-10-04 13:22                           ` Christian König
2021-10-04 13:27                             ` Jason Gunthorpe
2021-10-04 14:54                               ` Christian König
2021-09-28 20:05   ` Jason Gunthorpe
2021-09-29 21:46     ` Logan Gunthorpe
2021-09-16 23:41 ` [PATCH v3 20/20] nvme-pci: allow mmaping the CMB in userspace Logan Gunthorpe
2021-09-28 20:02 ` [PATCH v3 00/20] Userspace P2PDMA with O_DIRECT NVMe devices Jason Gunthorpe
2021-09-29 21:50   ` Logan Gunthorpe
2021-09-29 23:21     ` Jason Gunthorpe
2021-09-29 23:28       ` Logan Gunthorpe
2021-09-29 23:36         ` Jason Gunthorpe
2021-09-29 23:52           ` Logan Gunthorpe

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