linux-kernel - [PATCH v4 2/4] PCI: Fix serious bug when sizing bridges with additional size

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Date:   Wed, 17 Apr 2019 14:16:50 +0000
From:   Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "corbet@....net" <corbet@....net>,
        Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
Subject: [PATCH v4 2/4] PCI: Fix serious bug when sizing bridges with
 additional size

Change find_free_bus_resource function to not skip assigned resources
with non-null parent.

Add checks in pbus_size_io and pbus_size_mem to return success if
resource returned from find_free_bus_resource is already allocated.

This avoids pbus_size_io and pbus_size_mem returning error code to
__pci_bus_size_bridges when a resource has been successfully assigned in
a previous pass. This fixes the existing behaviour where space for a
resource could be reserved multiple times in different parent bridge
windows. This also greatly reduces the number of failed BAR messages in
dmesg when Linux assigns resources.

Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@...look.com.au>
---
 drivers/pci/setup-bus.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index a1ca8a11f..5b9ee9945 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -752,11 +752,17 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
 	}
 }
 
-/* Helper function for sizing routines: find first available
-   bus resource of a given type. Note: we intentionally skip
-   the bus resources which have already been assigned (that is,
-   have non-NULL parent resource). */
-static struct resource *find_free_bus_resource(struct pci_bus *bus,
+/*
+ * Helper function for sizing routines: find first bus resource of a given
+ * type. Note: we do not skip the bus resources which have already been
+ * assigned (r->parent != NULL). This is because a resource that is already
+ * assigned (nothing more to be done) will be indistinguishable from one that
+ * failed due to lack of space if we skip assigned resources. If the caller
+ * function cannot tell the difference then it might try to place the
+ * resources in a different window, doubling up on resources or causing
+ * unforeseeable issues.
+ */
+static struct resource *find_bus_resource_of_type(struct pci_bus *bus,
 			 unsigned long type_mask, unsigned long type)
 {
 	int i;
@@ -765,7 +771,7 @@ static struct resource *find_free_bus_resource(struct pci_bus *bus,
 	pci_bus_for_each_resource(bus, r, i) {
 		if (r == &ioport_resource || r == &iomem_resource)
 			continue;
-		if (r && (r->flags & type_mask) == type && !r->parent)
+		if (r && (r->flags & type_mask) == type)
 			return r;
 	}
 	return NULL;
@@ -863,14 +869,16 @@ static void pbus_size_io(struct pci_bus *bus, resource_size_t min_size,
 		resource_size_t add_size, struct list_head *realloc_head)
 {
 	struct pci_dev *dev;
-	struct resource *b_res = find_free_bus_resource(bus, IORESOURCE_IO,
-							IORESOURCE_IO);
+	struct resource *b_res = find_bus_resource_of_type(bus, IORESOURCE_IO,
+					IORESOURCE_IO);
 	resource_size_t size = 0, size0 = 0, size1 = 0;
 	resource_size_t children_add_size = 0;
 	resource_size_t min_align, align;
 
 	if (!b_res)
 		return;
+	if (b_res->parent)
+		return;
 
 	min_align = window_alignment(bus, IORESOURCE_IO);
 	list_for_each_entry(dev, &bus->devices, bus_list) {
@@ -975,7 +983,7 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 	resource_size_t min_align, align, size, size0, size1;
 	resource_size_t aligns[18];	/* Alignments from 1Mb to 128Gb */
 	int order, max_order;
-	struct resource *b_res = find_free_bus_resource(bus,
+	struct resource *b_res = find_bus_resource_of_type(bus,
 					mask | IORESOURCE_PREFETCH, type);
 	resource_size_t children_add_size = 0;
 	resource_size_t children_add_align = 0;
@@ -983,6 +991,8 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
 
 	if (!b_res)
 		return -ENOSPC;
+	if (b_res->parent)
+		return 0;
 
 	memset(aligns, 0, sizeof(aligns));
 	max_order = 0;
-- 
2.20.1