linux-kernel - [PATCH 11/13] PCI/P2PDMA: add helper pci_p2pdma_max_pagemap

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Message-Id: <20251220040446.274991-12-houtao@huaweicloud.com>
Date: Sat, 20 Dec 2025 12:04:44 +0800
From: Hou Tao <houtao@...weicloud.com>
To: linux-kernel@...r.kernel.org
Cc: linux-pci@...r.kernel.org,
	linux-mm@...ck.org,
	linux-nvme@...ts.infradead.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Logan Gunthorpe <logang@...tatee.com>,
	Alistair Popple <apopple@...dia.com>,
	Leon Romanovsky <leonro@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tejun Heo <tj@...nel.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Keith Busch <kbusch@...nel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>,
	houtao1@...wei.com
Subject: [PATCH 11/13] PCI/P2PDMA: add helper pci_p2pdma_max_pagemap_align()

From: Hou Tao <houtao1@...wei.com>

Add helper pci_p2pdma_max_pagemap_align() to find the max possible
alignment for p2p dma memory mapping in both userspace and kernel space.

When huge transparent page is supported, and the physical address, the
size of the BAR and the offset is {PUD|PMM}_SIZE aligned, it returns
{PUD|PMD_SIZE} accordingly. Otherwise, it returns PAGE_SIZE.

Signed-off-by: Hou Tao <houtao1@...wei.com>
---
 include/linux/pci-p2pdma.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/linux/pci-p2pdma.h b/include/linux/pci-p2pdma.h
index 2fa671274c45..5d940b9e5338 100644
--- a/include/linux/pci-p2pdma.h
+++ b/include/linux/pci-p2pdma.h
@@ -210,4 +210,30 @@ pci_p2pdma_bus_addr_map(struct p2pdma_provider *provider, phys_addr_t paddr)
 	return paddr + provider->bus_offset;
 }
 
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline size_t pci_p2pdma_max_pagemap_align(struct pci_dev *pdev, int bar,
+						  u64 size, u64 offset)
+{
+	resource_size_t start = pci_resource_start(pdev, bar);
+
+	if (has_transparent_pud_hugepage() &&
+	    IS_ALIGNED(start, PUD_SIZE) && IS_ALIGNED(size, PUD_SIZE) &&
+	    IS_ALIGNED(offset, PUD_SIZE))
+		return PUD_SIZE;
+
+	if (has_transparent_hugepage() &&
+	    IS_ALIGNED(start, PMD_SIZE) && IS_ALIGNED(size, PMD_SIZE) &&
+	    IS_ALIGNED(offset, PMD_SIZE))
+		return PMD_SIZE;
+
+	return PAGE_SIZE;
+}
+#else
+static inline size_t pci_p2pdma_max_pagemap_align(resource_size_t start,
+						  u64 size, u64 offset)
+{
+	return PAGE_SIZE;
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+
 #endif /* _LINUX_PCI_P2P_H */
-- 
2.29.2