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Wysocki" , Danilo Krummrich , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , houtao1@huawei.com References: <20251220040446.274991-1-houtao@huaweicloud.com> <20251220040446.274991-14-houtao@huaweicloud.com> Content-Language: en-CA From: Logan Gunthorpe In-Reply-To: <20251220040446.274991-14-houtao@huaweicloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: houtao@huaweicloud.com, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, linux-nvme@lists.infradead.org, bhelgaas@google.com, apopple@nvidia.com, leonro@nvidia.com, gregkh@linuxfoundation.org, tj@kernel.org, rafael@kernel.org, dakr@kernel.org, akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, kbusch@kernel.org, axboe@kernel.dk, hch@lst.de, sagi@grimberg.me, houtao1@huawei.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH 13/13] PCI/P2PDMA: enable compound page support for p2pdma memory X-SA-Exim-Version: 4.2.1 (built Sun, 23 Feb 2025 07:57:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) X-Rspam-User: X-Rspamd-Queue-Id: 4F753A000B X-Rspamd-Server: rspam04 X-Stat-Signature: gy4jqp9ydps3gdx6quauwkyn1e56oac4 X-HE-Tag: 1766423453-989781 X-HE-Meta: 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 URw6ymb4 YPBjnlPh+8y8Zf7E+Cvfli1a/Wrj9p/1wO36vVTvUhatOsepgCuK6TXFUGX3Wu745h4+Npv4zG2nQeZjRvKsYlQ3r7wHDtRVF1Y2494ZGSiomWV0VJSekoeDMmmdrCvQ03j4BZ5eX+3SxGXEpr5JnKLfwithl4CDTFuGaC6i6c06SNKGVymlpHc9sQwdiMo5bamArDgoW4vI8MUr5TZ59L1C3guui26NSi7sJHHqVCgNMG0tMrvD3Ig7EUXQEgr+2I+W3TZPFRX7jKCMterAY1UFcO0maiyEAp7SKS32UormRuUKpWQi9smCpVZd0K3Thxs5B1XZj1kH+eGw= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025-12-19 21:04, Hou Tao wrote: > From: Hou Tao > > Compound page support for P2PDMA memory in both kernel and user space is > now in place. Enable it by allowing PUD_SIZE and PMD_SIZE alignment. > > Signed-off-by: Hou Tao > --- > drivers/pci/p2pdma.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c > index 4a133219ac43..969bdacdcf8b 100644 > --- a/drivers/pci/p2pdma.c > +++ b/drivers/pci/p2pdma.c > @@ -452,9 +452,19 @@ static inline int pci_p2pdma_check_pagemap_align(struct pci_dev *pdev, int bar, > u64 size, size_t align, > u64 offset) > { > + if (has_transparent_pud_hugepage() && align == PUD_SIZE) > + goto more_check; > + if (has_transparent_hugepage() && align == PMD_SIZE) > + goto more_check; > if (align == PAGE_SIZE) > return 0; > return -EINVAL; > + > +more_check: > + if (IS_ALIGNED(pci_resource_start(pdev, bar), align) && > + IS_ALIGNED(size, align) && IS_ALIGNED(offset, align)) > + return 0; > + return -EINVAL; > } Again this seems strange. It's a bit unlikely to have a large BAR that wouldn't be well aligned, but this change is now requiring all P2P memory to be aligned to 1GB if the CPU supports PUDs. So if a particular device only has a small (say 256MB) imperfectly aligned bar it may now fail to be registered. I don't think the alignment should be a property of the device. When a mapping is created, if everything is aligned appropriately, and there is enough free aligned P2PDMA memory, then it should map a full PUD page. There shouldn't be other restrictions placed on the hardware to make this work. Logan