Re: [PATCH 1/2] pstore-ram: Fix hangs by using write-combine mappings
On Fri, Sep 12, 2014 at 11:32 AM, Tony Lindgren t...@atomide.com wrote:
From: Rob Herring robherri...@gmail.com
Currently trying to use pstore on at least ARMs can hang as we're
mapping the peristent RAM with pgprot_noncached().
On ARMs, pgprot_noncached() will actually make the memory strongly
ordered, and as the atomic operations pstore uses are implementation
defined for strongly ordered memory, they may not work. So basically
atomic operations have undefined behavior on ARM for device or strongly
ordered memory types.
Let's fix the issue by using write-combine variants for mappings. This
corresponds to normal, non-cacheable memory on ARM. For many other
architectures, this change does not change the mapping type as by
default we have:
#define pgprot_writecombine pgprot_noncached
The reason why pgprot_noncached() was originaly used for pstore
is because Colin Cross ccr...@android.com had observed lost
debug prints right before a device hanging write operation on some
systems. For the platforms supporting pgprot_noncached(), we can
add a an optional configuration option to support that. But let's
get pstore working first before adding new features.
Cc: Arnd Bergmann a...@arndb.de
Cc: Anton Vorontsov cbouatmai...@gmail.com
Cc: Colin Cross ccr...@android.com
Cc: Kees Cook keesc...@chromium.org
Cc: Olof Johansson o...@lixom.net
Cc: Tony Luck tony.l...@intel.com
Cc: linux-ker...@vger.kernel.org
Signed-off-by: Rob Herring rob.herr...@calxeda.com
[t...@atomide.com: updated description]
Signed-off-by: Tony Lindgren t...@atomide.com
Acked-by: Kees Cook keesc...@chromium.org
Please Cc: sta...@vger.kernel.org on this one too.
Thanks!
-Kees
---
fs/pstore/ram_core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index 9d7b9a8..24f94b0 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -392,7 +392,7 @@ static void *persistent_ram_vmap(phys_addr_t start,
size_t size)
page_start = start - offset_in_page(start);
page_count = DIV_ROUND_UP(size + offset_in_page(start), PAGE_SIZE);
- prot = pgprot_noncached(PAGE_KERNEL);
+ prot = pgprot_writecombine(PAGE_KERNEL);
pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
if (!pages) {
@@ -422,7 +422,7 @@ static void *persistent_ram_iomap(phys_addr_t start,
size_t size)
buffer_start_add = buffer_start_add_locked;
buffer_size_add = buffer_size_add_locked;
- return ioremap(start, size);
+ return ioremap_wc(start, size);
}
static int persistent_ram_buffer_map(phys_addr_t start, phys_addr_t size,
--
2.1.0
--
Kees Cook
Chrome OS Security
--
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[PATCH 1/2] pstore-ram: Fix hangs by using write-combine mappings
From: Rob Herring robherri...@gmail.com
Currently trying to use pstore on at least ARMs can hang as we're
mapping the peristent RAM with pgprot_noncached().
On ARMs, pgprot_noncached() will actually make the memory strongly
ordered, and as the atomic operations pstore uses are implementation
defined for strongly ordered memory, they may not work. So basically
atomic operations have undefined behavior on ARM for device or strongly
ordered memory types.
Let's fix the issue by using write-combine variants for mappings. This
corresponds to normal, non-cacheable memory on ARM. For many other
architectures, this change does not change the mapping type as by
default we have:
#define pgprot_writecombine pgprot_noncached
The reason why pgprot_noncached() was originaly used for pstore
is because Colin Cross ccr...@android.com had observed lost
debug prints right before a device hanging write operation on some
systems. For the platforms supporting pgprot_noncached(), we can
add a an optional configuration option to support that. But let's
get pstore working first before adding new features.
Cc: Arnd Bergmann a...@arndb.de
Cc: Anton Vorontsov cbouatmai...@gmail.com
Cc: Colin Cross ccr...@android.com
Cc: Kees Cook keesc...@chromium.org
Cc: Olof Johansson o...@lixom.net
Cc: Tony Luck tony.l...@intel.com
Cc: linux-ker...@vger.kernel.org
Signed-off-by: Rob Herring rob.herr...@calxeda.com
[t...@atomide.com: updated description]
Signed-off-by: Tony Lindgren t...@atomide.com
---
fs/pstore/ram_core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index 9d7b9a8..24f94b0 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -392,7 +392,7 @@ static void *persistent_ram_vmap(phys_addr_t start, size_t
size)
page_start = start - offset_in_page(start);
page_count = DIV_ROUND_UP(size + offset_in_page(start), PAGE_SIZE);
- prot = pgprot_noncached(PAGE_KERNEL);
+ prot = pgprot_writecombine(PAGE_KERNEL);
pages = kmalloc_array(page_count, sizeof(struct page *), GFP_KERNEL);
if (!pages) {
@@ -422,7 +422,7 @@ static void *persistent_ram_iomap(phys_addr_t start, size_t
size)
buffer_start_add = buffer_start_add_locked;
buffer_size_add = buffer_size_add_locked;
- return ioremap(start, size);
+ return ioremap_wc(start, size);
}
static int persistent_ram_buffer_map(phys_addr_t start, phys_addr_t size,
--
2.1.0
--
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