[PATCH v2 04/25] mm: enhance region_is_ram() to distinguish 'unknown' vs 'mixed'

Dan Williams
2015-07-25T02:44:07Z

region_is_ram() is used to prevent the establishment of aliased mappings
to physical "System RAM" with incompatible cache settings. However, it
uses "-1" to indicate both "unknown" memory ranges (ranges not described
by platform firmware) and "mixed" ranges (where the parameters describe
a range that partially overlaps "System RAM").

Fix this up by explicitly tracking the "unknown" vs "mixed" resource
cases. In addition to clarifying that "-1" means the requested spanned
RAM and non-RAM resource, this re-write also adds support for detecting
when the requested range completely covers all of a resource.

Finally, the implementation treats overlaps between "unknown" and RAM as
RAM.

Cc: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
kernel/resource.c | 43 +++++++++++++++++++++++--------------------
1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index fed052a1bc9f..119b282985f9 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -493,39 +493,42 @@ int __weak page_is_ram(unsigned long pfn)
EXPORT_SYMBOL_GPL(page_is_ram);

/*
- * Search for a resouce entry that fully contains the specified region.
- * If found, return 1 if it is RAM, 0 if not.
- * If not found, or region is not fully contained, return -1
+ * Check if the specified region partially overlaps or fully eclipses "System
+ * RAM". Return '0' if the region does not overlap RAM, return '-1' if the
+ * region overlaps RAM and another resource, and return '1' if the region
+ * overlaps RAM and no other defined resource. Note, that '1' is also returned
+ * in the case when the specified region overlaps RAM and undefined memory
+ * holes.
*
* Used by the ioremap functions to ensure the user is not remapping RAM and is
* a vast speed up over walking through the resource table page by page.
*/
int region_is_ram(resource_size_t start, unsigned long size)
{
- struct resource *p;
- resource_size_t end = start + size - 1;
unsigned long flags = IORESOURCE_MEM | IORESOURCE_BUSY;
+ resource_size_t end = start + size - 1;
const char *name = "System RAM";
- int ret = -1;
+ int ram = 0; int other = 0;
+ struct resource *p;

read_lock(&resource_lock);
for (p = iomem_resource.child; p ; p = p->sibling) {
- if (p->end < start)
- continue;
-
- if (p->start <= start && end <= p->end) {
- /* resource fully contains region */
- if ((p->flags != flags) || strcmp(p->name, name))
- ret = 0;
- else
- ret = 1;
- break;
- }
- if (end < p->start)
- break; /* not found */
+ bool is_ram = strcmp(p->name, name) == 0 && p->flags == flags;
+
+ if (start >= p->start && start <= p->end)
+ is_ram ? ram++ : other++;
+ if (end >= p->start && end <= p->end)
+ is_ram ? ram++ : other++;
+ if (p->start >= start && p->end <= end)
+ is_ram ? ram++ : other++;
}
read_unlock(&resource_lock);
- return ret;
+
+ if (other == 0)
+ return !!ram;
+ if (ram)
+ return -1;
+ return 0;
}

void __weak arch_remove_reservations(struct resource *avail)