memremap fix for 4.3 (v2)
Hi Linus, please pull from...
git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm libnvdimm-fixes
...to receive a reworked version of the memremap highmem fix. The change since v1 is dropping the kmap fallback.
---
The new memremap() api introduced in the 4.3 cycle to unify/replace ioremap_cache() and ioremap_wt() is mishandling the highmem case. This patch has received a build success notification from a 0day-kbuild-robot run and has received an ack from Ard.
The following changes since commit 25cb62b76430a91cc6195f902e61c2cb84ade622:
Linux 4.3-rc5 (2015-10-11 11:09:45 -0700)
are available in the git repository at:
git://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm libnvdimm-fixes
for you to fetch changes up to 182475b7a2831abf7e6ca83b2aced0bef5dcdfd3:
memremap: fix highmem support (2015-10-26 16:55:56 -0400)
----------------------------------------------------------------
Dan Williams (1):
memremap: fix highmem support
kernel/memremap.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-)
commit 182475b7a2831abf7e6ca83b2aced0bef5dcdfd3
Author: Dan Williams <[email protected]> Date: Mon Oct 26 16:55:56 2015 -0400
memremap: fix highmem support
Currently memremap checks if the range is "System RAM" and returns the kernel linear address. This is broken for highmem platforms where a range may be "System RAM", but is not part of the kernel linear mapping. Fallback to ioremap_cache() in these cases, to let the arch code attempt to handle it.
Note that ARM ioremap will WARN when attempting to remap ram, and in that case the caller needs to be fixed. For this reason, existing ioremap_cache() usages for ARM are already trained to avoid attempts to remap ram.
The impact of this bug is low for now since the pmem driver is the only user of memremap(), but this is important to fix before more conversions to memremap arrive in 4.4.
kernel/memremap.c +12 -2
@@ -24,6 +24,16 @@ __weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size) }#endif +static void *try_ram_remap (resource_size_t offset,size_t size) +{ +struct page *page =pfn_to_page (offset >>PAGE_SHIFT ); + +/* In the simple case just return the existing linear address */ +if (!PageHighMem (page)) +return __va (offset); +return NULL ;/* fallback to ioremap_cache */ +} +/** * memremap() - remap an iomem_resource as cacheable memory * @offset: iomem resource start address
@@ -66,8 +76,8 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)* the requested range is potentially in "System RAM" */ if (is_ram ==REGION_INTERSECTS ) - addr =__va (offset); -else + addr =try_ram_remap (offset, size); +if (!addr) addr =ioremap_cache (offset, size); }
Quoted 6 lines · Dan J
kernel/memremap.c +0
-0@@ -24,6 +24,16 @@ __weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size) }
kernel/memremap.c __weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size) · line 34
Quoted 10 lines
kernel/memremap.c +8
-0#endif +static void *try_ram_remap (resource_size_t offset,size_t size) +{ +struct page *page =pfn_to_page (offset >>PAGE_SHIFT ); + +/* In the simple case just return the existing linear address */ +if (!PageHighMem (page)) +return __va (offset); +return NULL ;/* fallback to ioremap_cache */
Right, so a highmem page results in this returning NULL, which will...
kernel/memremap.c void *memremap(resource_size_t offset, size_t size, unsigned long flags) · line 81
Quoted 9 lines
kernel/memremap.c +2
-2@@ -66,8 +76,8 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)* the requested range is potentially in "System RAM" */ if (is_ram ==REGION_INTERSECTS ) - addr =__va (offset); -else + addr =try_ram_remap (offset, size); +if (!addr) addr =ioremap_cache (offset, size);
cause ioremap_cache() to be called. That falls through on ARM to:
__arm_ioremap_pfn_caller()
and we will hit this (as I've mentioned before through explanation rather than quoting code):
/*
* Don't allow RAM to be mapped - this causes problems with ARMv6+
*/
if (WARN_ON(pfn_valid(pfn)))
return NULL;Signature · 2 lines
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
Quoted 34 lines · Russell King - ARM Linux
Quoted 6 lines · Dan J
kernel/memremap.c +0
-0@@ -24,6 +24,16 @@ __weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size) }kernel/memremap.c __weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size) · line 34
Quoted 10 lines
kernel/memremap.c +8
-0#endif +static void *try_ram_remap (resource_size_t offset,size_t size) +{ +struct page *page =pfn_to_page (offset >>PAGE_SHIFT ); + +/* In the simple case just return the existing linear address */ +if (!PageHighMem (page)) +return __va (offset); +return NULL ;/* fallback to ioremap_cache */ Right, so a highmem page results in this returning NULL, which will...
kernel/memremap.c void *memremap(resource_size_t offset, size_t size, unsigned long flags) · line 81
Quoted 9 lines
kernel/memremap.c +2
-2@@ -66,8 +76,8 @@ void *memremap(resource_size_t offset, size_t size, unsigned long flags)* the requested range is potentially in "System RAM" */ if (is_ram ==REGION_INTERSECTS ) - addr =__va (offset); -else + addr =try_ram_remap (offset, size); +if (!addr) addr =ioremap_cache (offset, size);cause
ioremap_cache()to be called. That falls through on ARM to:__arm_ioremap_pfn_caller()
Quoted 9 lines
and we will hit this (as I've mentioned before through explanation rather than quoting code):
/* * Don't allow RAM to be mapped - this causes problems with ARMv6+ */ if (WARN_ON(pfn_valid(pfn))) return NULL;
Right, which means the caller is broken and shouldn't be using memremap, same as misuse of ioremap_cache today.