PCI: Honor alignment overrides

Started by Ilpo Järvinen on Nov 6, 2026

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REVIEWED · 1 review, 1 by a maintainer

Status: Reviewed.

Revision v5 (2 revisions archived); 1 review trailer (1 from subsystem maintainers).

Revisions (2)
  1. v3
  2. v5 current [diff against previous]

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Ilpo Järvinen

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pci=resource_alignment argument can override the default alignment for
the resource. The remainder code introduced in the commit 9036bd0efcb6
("PCI: Align head space better") can move remainder space (non-aligning
part of the size) before the aligning left edge which results in
violating the requested alignment.

Introduce struct pci_resreq_data to hold device and user-given alignment
to be able to honor it in pci_align_resource(). When user-given alignment
is found, any remainder movement is skipped.

PowerNV will not be able to use the current remainder logic after this
change because on it pcibios_default_alignment() always results in
setting min_align but this code is in a transient state and the problem
will be fixed by an upcoming change that rewrites the resource
placement algorithm with a more generic approach.

Fixes: 9036bd0efcb6 ("PCI: Align head space better")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Link: https://lore.kernel.org/linux-pci/20260923133202.07DF61F000FF@smtp.kernel.org/
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---

Jani Nikula [off-list ref] did ack this with a condition that
there is a proper review done by somebody else so I've not yet included
his tag.

 arch/alpha/kernel/pci.c          |  3 ++-
 arch/arm/kernel/bios32.c         |  5 +++--
 arch/m68k/kernel/pcibios.c       |  4 ++--
 arch/mips/pci/pci-generic.c      |  5 +++--
 arch/mips/pci/pci-legacy.c       |  5 +++--
 arch/parisc/kernel/pci.c         |  5 +++--
 arch/powerpc/kernel/pci-common.c |  5 +++--
 arch/sh/drivers/pci/pci.c        |  5 +++--
 arch/x86/pci/i386.c              |  5 +++--
 arch/xtensa/kernel/pci.c         |  5 +++--
 drivers/char/agp/intel-gtt.c     |  5 ++++-
 drivers/gpu/drm/i915/i915_gmch.c |  5 +++--
 drivers/pci/pci.c                |  4 ++--
 drivers/pci/pci.h                |  2 ++
 drivers/pci/setup-res.c          | 33 ++++++++++++++++++++++++++------
 include/linux/pci.h              | 15 +++++++++++++--
 16 files changed, 79 insertions(+), 32 deletions(-)

diff --git a/arch/alpha/kernel/pci.c b/arch/alpha/kernel/pci.c
index 11df411b1d18..c5d725a9781f 100644
--- a/arch/alpha/kernel/pci.c
+++ b/arch/alpha/kernel/pci.c
@@ -128,7 +128,8 @@ pcibios_align_resource(void *data, const struct resource *res,
 		       const struct resource *empty_res,
 		       resource_size_t size, resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	struct pci_controller *hose = dev->sysdata;
 	unsigned long alignto;
 	resource_size_t start = res->start;
diff --git a/arch/arm/kernel/bios32.c b/arch/arm/kernel/bios32.c
index ac0e890510da..3e61826f07fb 100644
--- a/arch/arm/kernel/bios32.c
+++ b/arch/arm/kernel/bios32.c
@@ -564,7 +564,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				       resource_size_t size,
 				       resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	resource_size_t start = res->start;
 	struct pci_host_bridge *host_bridge;
 
@@ -578,7 +579,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				start, size, align);
 
 	if (res->flags & IORESOURCE_MEM)
-		return pci_align_resource(dev, res, empty_res, size, align);
+		return pci_align_resource(rr, res, empty_res, size, align);
 
 	return start;
 }
diff --git a/arch/m68k/kernel/pcibios.c b/arch/m68k/kernel/pcibios.c
index 7a9e60df79c5..3024408412bc 100644
--- a/arch/m68k/kernel/pcibios.c
+++ b/arch/m68k/kernel/pcibios.c
@@ -31,14 +31,14 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				       resource_size_t size,
 				       resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
 	resource_size_t start = res->start;
 
 	if ((res->flags & IORESOURCE_IO) && (start & 0x300))
 		start = (start + 0x3ff) & ~0x3ff;
 
 	if (res->flags & IORESOURCE_MEM)
-		return pci_align_resource(dev, res, empty_res, size, align);
+		return pci_align_resource(rr, res, empty_res, size, align);
 
 	return start;
 }
diff --git a/arch/mips/pci/pci-generic.c b/arch/mips/pci/pci-generic.c
index c2e23d0c1d77..7f3ecb91b85b 100644
--- a/arch/mips/pci/pci-generic.c
+++ b/arch/mips/pci/pci-generic.c
@@ -25,7 +25,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				       const struct resource *empty_res,
 				       resource_size_t size, resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	resource_size_t start = res->start;
 	struct pci_host_bridge *host_bridge;
 
@@ -39,7 +40,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				start, size, align);
 
 	if (res->flags & IORESOURCE_MEM)
-		return pci_align_resource(dev, res, empty_res, size, align);
+		return pci_align_resource(rr, res, empty_res, size, align);
 
 	return start;
 }
diff --git a/arch/mips/pci/pci-legacy.c b/arch/mips/pci/pci-legacy.c
index dae6dafdd6e0..82d4b01db64e 100644
--- a/arch/mips/pci/pci-legacy.c
+++ b/arch/mips/pci/pci-legacy.c
@@ -55,7 +55,8 @@ pcibios_align_resource(void *data, const struct resource *res,
 		       const struct resource *empty_res,
 		       resource_size_t size, resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	struct pci_controller *hose = dev->sysdata;
 	resource_size_t start = res->start;
 
@@ -70,7 +71,7 @@ pcibios_align_resource(void *data, const struct resource *res,
 		if (start & 0x300)
 			start = (start + 0x3ff) & ~0x3ff;
 	} else if (res->flags & IORESOURCE_MEM) {
-		start = pci_align_resource(dev, res, empty_res, size, align);
+		start = pci_align_resource(rr, res, empty_res, size, align);
 
 		/* Make sure we start at our min on all hoses */
 		if (start < PCIBIOS_MIN_MEM + hose->mem_resource->start)
diff --git a/arch/parisc/kernel/pci.c b/arch/parisc/kernel/pci.c
index 96950fe9c2b7..36a3a439f609 100644
--- a/arch/parisc/kernel/pci.c
+++ b/arch/parisc/kernel/pci.c
@@ -193,7 +193,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				       resource_size_t size,
 				       resource_size_t alignment)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	resource_size_t align, start = res->start;
 
 	pci_dbg(dev, "%pR: pcibios_align_resource(%lx, 0x%llx, 0x%llx)\n",
@@ -205,7 +206,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 	if (align > alignment)
 		start = ALIGN(start, align);
 	else
-		start = pci_align_resource(dev, res, empty_res, size, alignment);
+		start = pci_align_resource(rr, res, empty_res, size, alignment);
 
 	return start;
 }
diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index 4fc52c21fe5d..23594759cfe2 100644
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c
@@ -1131,7 +1131,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				       resource_size_t size,
 				       resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	resource_size_t start = res->start;
 
 	if (res->flags & IORESOURCE_IO) {
@@ -1140,7 +1141,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 		if (start & 0x300)
 			start = (start + 0x3ff) & ~0x3ff;
 	} else if (res->flags & IORESOURCE_MEM) {
-		start = pci_align_resource(dev, res, empty_res, size, align);
+		start = pci_align_resource(rr, res, empty_res, size, align);
 	}
 
 	return start;
diff --git a/arch/sh/drivers/pci/pci.c b/arch/sh/drivers/pci/pci.c
index 878a27a1acfb..279f2770ff4b 100644
--- a/arch/sh/drivers/pci/pci.c
+++ b/arch/sh/drivers/pci/pci.c
@@ -172,7 +172,8 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				       resource_size_t size,
 				       resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	struct pci_channel *hose = dev->sysdata;
 	resource_size_t start = res->start;
 
@@ -186,7 +187,7 @@ resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 		if (start & 0x300)
 			start = (start + 0x3ff) & ~0x3ff;
 	} else if (res->flags & IORESOURCE_MEM) {
-		start = pci_align_resource(dev, res, empty_res, size, align);
+		start = pci_align_resource(rr, res, empty_res, size, align);
 	}
 
 	return start;
diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index e2de26b82940..4178ae4380c2 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -156,7 +156,8 @@ pcibios_align_resource(void *data, const struct resource *res,
 		       const struct resource *empty_res,
 		       resource_size_t size, resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	resource_size_t start = res->start;
 
 	if (res->flags & IORESOURCE_IO) {
@@ -165,7 +166,7 @@ pcibios_align_resource(void *data, const struct resource *res,
 		if (start & 0x300)
 			start = (start + 0x3ff) & ~0x3ff;
 	} else if (res->flags & IORESOURCE_MEM) {
-		start = pci_align_resource(dev, res, empty_res, size, align);
+		start = pci_align_resource(rr, res, empty_res, size, align);
 
 		/* The low 1MB range is reserved for ISA cards */
 		if (start < BIOS_END)
diff --git a/arch/xtensa/kernel/pci.c b/arch/xtensa/kernel/pci.c
index 305031551136..4e8ad4a3c9fe 100644
--- a/arch/xtensa/kernel/pci.c
+++ b/arch/xtensa/kernel/pci.c
@@ -42,7 +42,8 @@ pcibios_align_resource(void *data, const struct resource *res,
 		       const struct resource *empty_res,
 		       resource_size_t size, resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
+	struct pci_dev *dev = rr->dev;
 	resource_size_t start = res->start;
 
 	if (res->flags & IORESOURCE_IO) {
@@ -55,7 +56,7 @@ pcibios_align_resource(void *data, const struct resource *res,
 		if (start & 0x300)
 			start = (start + 0x3ff) & ~0x3ff;
 	} else if (res->flags & IORESOURCE_MEM) {
-		start = pci_align_resource(dev, res, empty_res, size, align);
+		start = pci_align_resource(rr, res, empty_res, size, align);
 	}
 
 	return start;
diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
index bcc26785175d..06990fad8e48 100644
--- a/drivers/char/agp/intel-gtt.c
+++ b/drivers/char/agp/intel-gtt.c
@@ -1038,10 +1038,13 @@ static struct agp_memory *intel_fake_agp_alloc_by_type(size_t pg_count,
 
 static int intel_alloc_chipset_flush_resource(void)
 {
+	struct pci_resreq_data rr;
 	int ret;
+
+	pci_init_resreq_data(&rr, intel_private.bridge_dev);
 	ret = pci_bus_alloc_resource(intel_private.bridge_dev->bus, &intel_private.ifp_resource, PAGE_SIZE,
 				     PAGE_SIZE, PCIBIOS_MIN_MEM, 0,
-				     pcibios_align_resource, intel_private.bridge_dev);
+				     pcibios_align_resource, &rr);
 
 	return ret;
 }
diff --git a/drivers/gpu/drm/i915/i915_gmch.c b/drivers/gpu/drm/i915/i915_gmch.c
index b0ef6ef577a3..f11ed5509095 100644
--- a/drivers/gpu/drm/i915/i915_gmch.c
+++ b/drivers/gpu/drm/i915/i915_gmch.c
@@ -38,6 +38,7 @@ static int mchbar_reg(struct drm_i915_private *i915)
 static int
 intel_alloc_mchbar_resource(struct drm_i915_private *i915)
 {
+	struct pci_resreq_data rr;
 	u32 temp_lo, temp_hi = 0;
 	u64 mchbar_addr;
 	int ret;
@@ -55,12 +56,12 @@ intel_alloc_mchbar_resource(struct drm_i915_private *i915)
 	/* Get some space for it */
 	i915->gmch.mch_res.name = "i915 MCHBAR";
 	i915->gmch.mch_res.flags = IORESOURCE_MEM;
+	pci_init_resreq_data(&rr, i915->gmch.pdev);
 	ret = pci_bus_alloc_resource(i915->gmch.pdev->bus,
 				     &i915->gmch.mch_res,
 				     MCHBAR_SIZE, MCHBAR_SIZE,
 				     PCIBIOS_MIN_MEM,
-				     0, pcibios_align_resource,
-				     i915->gmch.pdev);
+				     0, pcibios_align_resource, &rr);
 	if (ret) {
 		drm_dbg(&i915->drm, "failed bus alloc: %d\n", ret);
 		i915->gmch.mch_res.start = 0;
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 7c6f2aba8144..8c40f86d75ee 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -6507,8 +6507,8 @@ static DEFINE_SPINLOCK(resource_alignment_lock);
  * RETURNS: Resource alignment if it is specified.
  *          Zero if it is not specified.
  */
-static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
-							bool *resize)
+resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
+						 bool *resize)
 {
 	int align_order, count;
 	resource_size_t align = pcibios_default_alignment();
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 77efa4c5c960..e6e2afcceb33 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -515,6 +515,8 @@ void devm_pci_alloc_host_bridge_release(void *data);
 struct device *pci_get_host_bridge_device(struct pci_dev *dev);
 void pci_put_host_bridge_device(struct device *dev);
 
+resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
+						 bool *resize);
 void pci_resize_resource_set_size(struct pci_dev *dev, int resno, int size);
 int pci_do_resource_release_and_resize(struct pci_dev *dev, int resno, int size,
 				       int exclude_bars);
diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c
index 376f09630a4a..9c55b9f9462c 100644
--- a/drivers/pci/setup-res.c
+++ b/drivers/pci/setup-res.c
@@ -248,6 +248,20 @@ static int pci_revert_fw_address(struct resource *res, struct pci_dev *dev,
 	return 0;
 }
 
+/*
+ * TODO: Improve PCI resource assignment interface so that callers outside PCI
+ * core do not need to know about this detail.
+ */
+void pci_init_resreq_data(struct pci_resreq_data *rr, struct pci_dev *dev)
+{
+	bool dummy;
+
+	memset(rr, 0, sizeof(*rr));
+	rr->dev = dev;
+	rr->min_align = pci_specified_resource_alignment(dev, &dummy);
+}
+EXPORT_SYMBOL_GPL(pci_init_resreq_data);
+
 resource_size_t pci_resource_alignment(const struct pci_dev *dev,
 				       const struct resource *res)
 {
@@ -265,17 +279,21 @@ resource_size_t pci_resource_alignment(const struct pci_dev *dev,
  * before res->start if there's enough free space there. This enables
  * tighter packing for resources.
  */
-resource_size_t pci_align_resource(struct pci_dev *dev,
+resource_size_t pci_align_resource(struct pci_resreq_data *rr,
 				   const struct resource *res,
 				   const struct resource *empty_res,
 				   resource_size_t size,
 				   resource_size_t align)
 {
+	struct pci_dev *dev = rr->dev;
 	resource_size_t remainder, start_addr;
 
 	if (!(res->flags & IORESOURCE_MEM))
 		return res->start;
 
+	if (rr->min_align)
+		return res->start;
+
 	if (IS_ALIGNED(size, align))
 		return res->start;
 
@@ -306,18 +324,21 @@ resource_size_t __weak pcibios_align_resource(void *data,
 					      resource_size_t size,
 					      resource_size_t align)
 {
-	struct pci_dev *dev = data;
+	struct pci_resreq_data *rr = data;
 
-	return pci_align_resource(dev, res, empty_res, size, align);
+	return pci_align_resource(rr, res, empty_res, size, align);
 }
 
 static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
 		int resno, resource_size_t size, resource_size_t align)
 {
 	struct resource *res = pci_resource_n(dev, resno);
+	struct pci_resreq_data rr;
 	resource_size_t min;
 	int ret;
 
+	pci_init_resreq_data(&rr, dev);
+
 	min = (res->flags & IORESOURCE_IO) ? PCIBIOS_MIN_IO : PCIBIOS_MIN_MEM;
 
 	/*
@@ -329,7 +350,7 @@ static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
 	 */
 	ret = pci_bus_alloc_resource(bus, res, size, align, min,
 				     IORESOURCE_PREFETCH | IORESOURCE_MEM_64,
-				     pcibios_align_resource, dev);
+				     pcibios_align_resource, &rr);
 	if (ret == 0)
 		return 0;
 
@@ -341,7 +362,7 @@ static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
 	     (IORESOURCE_PREFETCH | IORESOURCE_MEM_64)) {
 		ret = pci_bus_alloc_resource(bus, res, size, align, min,
 					     IORESOURCE_PREFETCH,
-					     pcibios_align_resource, dev);
+					     pcibios_align_resource, &rr);
 		if (ret == 0)
 			return 0;
 	}
@@ -354,7 +375,7 @@ static int __pci_assign_resource(struct pci_bus *bus, struct pci_dev *dev,
 	 */
 	if (res->flags & (IORESOURCE_PREFETCH | IORESOURCE_MEM_64))
 		ret = pci_bus_alloc_resource(bus, res, size, align, min, 0,
-					     pcibios_align_resource, dev);
+					     pcibios_align_resource, &rr);
 
 	return ret;
 }
diff --git a/include/linux/pci.h b/include/linux/pci.h
index aa3765a20a96..c945f5753e7c 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1221,12 +1221,23 @@ int __must_check pcibios_enable_device(struct pci_dev *, int mask);
 /* Architecture-specific versions may override this (weak) */
 char *pcibios_setup(char *str);
 
-/* Used only when drivers/pci/setup.c is used */
+/**
+ * struct pci_resreq_data - Data passed to pcibios_align_resource()
+ * @dev: PCI device
+ * @min_align: Minimum alignment bound (from pci=resource_alignment or arch)
+ */
+struct pci_resreq_data {
+	struct pci_dev *dev;
+	resource_size_t min_align;
+};
+
+void pci_init_resreq_data(struct pci_resreq_data *rr, struct pci_dev *dev);
+
 resource_size_t pcibios_align_resource(void *data, const struct resource *res,
 				       const struct resource *empty_res,
 				       resource_size_t size,
 				       resource_size_t align);
-resource_size_t pci_align_resource(struct pci_dev *dev,
+resource_size_t pci_align_resource(struct pci_resreq_data *rr,
 				   const struct resource *res,
 				   const struct resource *empty_res,
 				   resource_size_t size,
-- 
2.47.3
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