linux-kernel - [PATCH v5 1/2] PCI: endpoint: improve fixed_size bar handling when allocating space

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Message-Id: <20250424-pci-ep-size-alignment-v5-1-2d4ec2af23f5@baylibre.com>
Date: Thu, 24 Apr 2025 10:34:04 +0200
From: Jerome Brunet <jbrunet@...libre.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, 
 Krzysztof Wilczyński <kw@...ux.com>, 
 Kishon Vijay Abraham I <kishon@...nel.org>, 
 Bjorn Helgaas <bhelgaas@...gle.com>, 
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Jon Mason <jdmason@...zu.us>, 
 Dave Jiang <dave.jiang@...el.com>, Allen Hubbe <allenbh@...il.com>, 
 Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>, 
 Chaitanya Kulkarni <kch@...dia.com>
Cc: Marek Vasut <marek.vasut+renesas@...il.com>, 
 Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, 
 Yuya Hamamachi <yuya.hamamachi.sx@...esas.com>, linux-pci@...r.kernel.org, 
 linux-kernel@...r.kernel.org, ntb@...ts.linux.dev, 
 linux-nvme@...ts.infradead.org, Jerome Brunet <jbrunet@...libre.com>, 
 Niklas Cassel <cassel@...nel.org>
Subject: [PATCH v5 1/2] PCI: endpoint: improve fixed_size bar handling when
 allocating space

When trying to allocate space for an endpoint function on a BAR with a
fixed size, the size saved in the 'struct pci_epf_bar' should be the fixed
size. This is expected by pci_epc_set_bar().

However, if the fixed_size is smaller that the alignment, the size saved
in the 'struct pci_epf_bar' matches the alignment and it is a problem for
pci_epc_set_bar().

To solve this, continue to allocate space that match the iATU alignment
requirement, saving it as .aligned_size, then save the size that matches
what is present in the BAR.

Fixes: 2a9a801620ef ("PCI: endpoint: Add support to specify alignment for buffers allocated to BARs")
Reviewed-by: Niklas Cassel <cassel@...nel.org>
Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
---
 drivers/pci/endpoint/pci-epf-core.c | 21 ++++++++++++++-------
 include/linux/pci-epf.h             |  3 +++
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
index 394395c7f8decfa2010469655a4bd58a002993fd..982db6c1fbe77653f6a74a31df5c4e997507d2d8 100644
--- a/drivers/pci/endpoint/pci-epf-core.c
+++ b/drivers/pci/endpoint/pci-epf-core.c
@@ -236,12 +236,13 @@ void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar,
 	}
 
 	dev = epc->dev.parent;
-	dma_free_coherent(dev, epf_bar[bar].size, addr,
+	dma_free_coherent(dev, epf_bar[bar].aligned_size, addr,
 			  epf_bar[bar].phys_addr);
 
 	epf_bar[bar].phys_addr = 0;
 	epf_bar[bar].addr = NULL;
 	epf_bar[bar].size = 0;
+	epf_bar[bar].aligned_size = 0;
 	epf_bar[bar].barno = 0;
 	epf_bar[bar].flags = 0;
 }
@@ -264,7 +265,7 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
 			  enum pci_epc_interface_type type)
 {
 	u64 bar_fixed_size = epc_features->bar[bar].fixed_size;
-	size_t align = epc_features->align;
+	size_t aligned_size, align = epc_features->align;
 	struct pci_epf_bar *epf_bar;
 	dma_addr_t phys_addr;
 	struct pci_epc *epc;
@@ -285,12 +286,17 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
 			return NULL;
 		}
 		size = bar_fixed_size;
+	} else {
+		/* BAR size must be power of two */
+		size = roundup_pow_of_two(size);
 	}
 
-	if (align)
-		size = ALIGN(size, align);
-	else
-		size = roundup_pow_of_two(size);
+	/*
+	 * Allocate enough memory to accommodate the iATU alignment requirement.
+	 * In most cases, this will be the same as .size but it might be different
+	 * if, for example, the fixed size of a BAR is smaller than align.
+	 */
+	aligned_size = align ? ALIGN(size, align) : size;
 
 	if (type == PRIMARY_INTERFACE) {
 		epc = epf->epc;
@@ -301,7 +307,7 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
 	}
 
 	dev = epc->dev.parent;
-	space = dma_alloc_coherent(dev, size, &phys_addr, GFP_KERNEL);
+	space = dma_alloc_coherent(dev, aligned_size, &phys_addr, GFP_KERNEL);
 	if (!space) {
 		dev_err(dev, "failed to allocate mem space\n");
 		return NULL;
@@ -310,6 +316,7 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
 	epf_bar[bar].phys_addr = phys_addr;
 	epf_bar[bar].addr = space;
 	epf_bar[bar].size = size;
+	epf_bar[bar].aligned_size = aligned_size;
 	epf_bar[bar].barno = bar;
 	if (upper_32_bits(size) || epc_features->bar[bar].only_64bit)
 		epf_bar[bar].flags |= PCI_BASE_ADDRESS_MEM_TYPE_64;
diff --git a/include/linux/pci-epf.h b/include/linux/pci-epf.h
index 879d19cebd4fc6d8df9d724e3a52fa7fbd61e535..749cee0bcf2cc0600ad3be1582b0c497c5a21bed 100644
--- a/include/linux/pci-epf.h
+++ b/include/linux/pci-epf.h
@@ -114,6 +114,8 @@ struct pci_epf_driver {
  * @phys_addr: physical address that should be mapped to the BAR
  * @addr: virtual address corresponding to the @phys_addr
  * @size: the size of the address space present in BAR
+ * @aligned_size: the size actually allocated to accommodate the iATU alignment
+ *                requirement
  * @barno: BAR number
  * @flags: flags that are set for the BAR
  */
@@ -121,6 +123,7 @@ struct pci_epf_bar {
 	dma_addr_t	phys_addr;
 	void		*addr;
 	size_t		size;
+	size_t		aligned_size;
 	enum pci_barno	barno;
 	int		flags;
 };

-- 
2.47.2