linux-kernel - [RFC PATCH 10/13] pci: pcsc: Use contiguous pages for the cache data

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Message-ID: <914285f708739992f14c16fb3be336c6e8afed52.1759312886.git.epetron@amazon.de>
Date: Fri, 3 Oct 2025 09:00:46 +0000
From: Evangelos Petrongonas <epetron@...zon.de>
To: Bjorn Helgaas <bhelgaas@...gle.com>, Alex Williamson
	<alex.williamson@...hat.com>, "Rafael J . Wysocki" <rafael@...nel.org>, "Len
 Brown" <lenb@...nel.org>
CC: Evangelos Petrongonas <epetron@...zon.de>, Pasha Tatashin
	<pasha.tatashin@...een.com>, David Matlack <dmatlack@...gle.com>, "Vipin
 Sharma" <vipinsh@...gle.com>, Chris Li <chrisl@...nel.org>, Jason Miu
	<jasonmiu@...gle.com>, Pratyush Yadav <pratyush@...nel.org>, "Stanislav
 Spassov" <stanspas@...zon.de>, <linux-pci@...r.kernel.org>,
	<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<nh-open-source@...zon.com>
Subject: [RFC PATCH 10/13] pci: pcsc: Use contiguous pages for the cache data

This patch refactors PCSC to use a single contiguous memory block for
all per-device data. This improves memory allocation efficiency.

This is a preparatory step for KHO persistence support, as it is easier
to manipulate physically continuous pages.

Signed-off-by: Evangelos Petrongonas <epetron@...zon.de>
---
 drivers/pci/pcsc.c   | 28 ++++++++++++++++++++++++----
 include/linux/pcsc.h | 32 ++++++++++++++++++++++++++++++--
 2 files changed, 54 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/pcsc.c b/drivers/pci/pcsc.c
index 304239b7ff8a..18d508f76649 100644
--- a/drivers/pci/pcsc.c
+++ b/drivers/pci/pcsc.c
@@ -725,6 +725,7 @@ int pcsc_add_device(struct pci_dev *dev)
 {
 	struct pcsc_node *node;
 	struct pci_bus *bus;
+	size_t data_size;
 
 	if (WARN_ON(!dev))
 		return -EINVAL;
@@ -741,12 +742,27 @@ int pcsc_add_device(struct pci_dev *dev)
 	 * nodes for these devices, as it simplifies the code flow
 	 */
 	if (dev->hdr_type == PCI_HEADER_TYPE_NORMAL) {
-		dev->pcsc->cfg_space = kzalloc(PCSC_CFG_SPC_SIZE, GFP_KERNEL);
-		if (!dev->pcsc->cfg_space)
+		/* Allocate contiguous, page aligned data block. This will be
+		 * needed for persisting the data with KHO.
+		 */
+		data_size = sizeof(struct pcsc_data);
+
+		dev->pcsc->data =
+			(struct pcsc_data *)__get_free_pages(
+				GFP_KERNEL | __GFP_ZERO, get_order(data_size));
+		if (!dev->pcsc->data)
+
 			goto err_free_node;
 
+		dev->pcsc->cachable_bitmask = dev->pcsc->data->cachable_bitmask;
+		dev->pcsc->cached_bitmask = dev->pcsc->data->cached_bitmask;
+		dev->pcsc->cfg_space = dev->pcsc->data->cfg_space;
+
 		infer_cacheability(dev);
 	} else {
+		dev->pcsc->data = NULL;
+		dev->pcsc->cachable_bitmask = NULL;
+		dev->pcsc->cached_bitmask = NULL;
 		dev->pcsc->cfg_space = NULL;
 	}
 
@@ -771,8 +787,12 @@ int pcsc_remove_device(struct pci_dev *dev)
 
 	atomic_dec(&num_nodes);
 
-	if (dev->pcsc && dev->pcsc->cfg_space) {
-		kfree(dev->pcsc->cfg_space);
+	if (dev->pcsc && dev->pcsc->data) {
+		size_t data_size = sizeof(struct pcsc_data);
+		size_t total_size = PAGE_ALIGN(data_size);
+
+		free_pages((unsigned long)dev->pcsc->data,
+			get_order(total_size));
 		kfree(dev->pcsc);
 	}
 	dev->pcsc = NULL;
diff --git a/include/linux/pcsc.h b/include/linux/pcsc.h
index 85471273c0a9..88894f641257 100644
--- a/include/linux/pcsc.h
+++ b/include/linux/pcsc.h
@@ -18,12 +18,40 @@
 #define PCSC_CFG_SPC_SIZE 256
 #endif
 
-struct pcsc_node {
-	u8 *cfg_space;
+/*
+ * struct pcsc__data - Continuous data block for PCSC
+ *
+ * This structure contains all the PCSC data in a single continuous
+ * memory block.
+ *
+ * @cfg_space: Configuration space cache
+ * @cachable_bitmask: Bitmap of cacheable configuration space offsets
+ * @cached_bitmask: Bitmap of cached configuration space offsets
+ */
+struct pcsc_data {
+	u8 cfg_space[PCSC_CFG_SPC_SIZE];
 	DECLARE_BITMAP(cachable_bitmask, PCSC_CFG_SPC_SIZE);
 	DECLARE_BITMAP(cached_bitmask, PCSC_CFG_SPC_SIZE);
 };
 
+/*
+ * struct pcsc_node - PCSC node structure
+ *
+ * This structure represents a PCSC node for a PCI device.
+ * It contains pointers into the data block for convenient access.
+ *
+ * @data: Pointer to the continuous data block
+ * @cachable_bitmask: Pointer to cachable_bitmask in data
+ * @cached_bitmask: Pointer to cached_bitmask in data
+ * @cfg_space: Pointer to cfg_space in data
+ */
+struct pcsc_node {
+	struct pcsc_data *data; /* Pointer to continuous data block */
+	unsigned long *cachable_bitmask; /* Convenience pointer into data */
+	unsigned long *cached_bitmask; /* Convenience pointer into data */
+	u8 *cfg_space; /* Convenience pointer into data */
+};
+
 /**
  * pcsc_hw_config_read - Direct hardware PCI config space read
  * @bus: PCI bus
-- 
2.47.3




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