On 5 February 2015 at 17:48, Catalin Marinas catalin.marinas@arm.com wrote:
On Thu, Feb 05, 2015 at 04:42:19PM +0000, Al Stone wrote:
On 02/05/2015 06:54 AM, Mark Salter wrote:
On Thu, 2015-02-05 at 10:41 +0000, Catalin Marinas wrote:
On Wed, Feb 04, 2015 at 06:58:14PM +0000, Mark Salter wrote:
On Wed, 2015-02-04 at 17:57 +0000, Catalin Marinas wrote:
On Wed, Feb 04, 2015 at 04:08:27PM +0000, Mark Salter wrote: > acpi_os_remap() is used to map ACPI tables. These tables may be in ram > which are already included in the kernel's linear RAM mapping. So we > need ioremap_cache to avoid two mappings to the same physical page > having different caching attributes.
What's the call path to acpi_os_ioremap() on such tables already in the linear mapping? I can see an acpi_map() function which already takes care of the RAM mapping case but there are other cases where acpi_os_ioremap() is called directly. For example, acpi_os_read_memory(), can it be called on both RAM and I/O?
acpi_map() is the one I've seen.
By default, if should_use_kmap() is not patched for arm64, it translates to page_is_ram(); acpi_map() would simply use a kmap() which returns the current kernel linear mapping on arm64.
The problem with kmap() is that it only maps a single page. I've seen tables over 4k which is why I patched acpi_map() not to use kmap() on arm64.
Right. Mark replied to this before I could; using kmap() enforced a 4k (one page) limit that we kept breaking with some ACPI tables being larger than that (DSDTs and SSDTs, fwiw). This would lead to some very odd behaviors when most but not all of a device definition was within the page; using the table checksums was one way of detecting the issues.
OK. So I think Mark's original patch was ok, assuming that the System Memory cases mentioned by Graeme are detected with page_is_ram().
page_is_ram() returns whether a pfn is covered by the linear mapping, so memory before the kernel or after a mem= limit will be misidentified.