On 24 November 2016 at 19:26, Robert Richter <robert.richter@xxxxxxxxxx> wrote: > Ard, > >> > >> On 24 November 2016 at 13:51, Robert Richter <robert.richter@xxxxxxxxxx> wrote: >> > >> > On 24.11.16 13:44:31, Ard Biesheuvel wrote: > >> > >> Regions containing firmware tables are owned by the firmware, and it >> > >> is the firmware that tells us which memory attributes we are allowed >> > >> to use. If those attributes include WB, it is perfectly legal to use a >> > >> cacheable mapping. That does *not* mean they should be covered by the >> > >> linear mapping. The linear mapping is read-write-non-exec, for >> > >> instance, and we may prefer to use a read-only mapping and/or >> > >> executable mapping. >> > > >> > > Ok, I am going to fix try_ram_remap(). > > I revisited the code and it is working well already since: > > e7cd190385d1 arm64: mark reserved memblock regions explicitly in iomem > > Now, try_ram_remap() is only called if the region to be mapped is > entirely in IORESOURCE_SYSTEM_RAM. This is only true for normal mem > ranges and not NOMAP mem. region_intersects() then returns > REGION_INTERSECTS and calls try_ram_remap(). For the NOMAP memory case > REGION_DISJOINT would be returned and thus arch_memremap_wb() being > called directly. Before the e7cd190385d1 change try_ram_remap() was > called also for nomap regions. > > So we can leave memremap() as it is and just apply this patch > unmodified. What do you think? I agree. The pfn_valid() check in try_ram_remap() is still appropriate simply because the PageHighmem check requires a valid struct page. But if we don't enter that code path anymore for NOMAP regions, I think we're ok. > Please ack. > I still don't fully understand how it is guaranteed that *all* memory (i.e., all regions for which memblock_is_memory() returns true) is covered by a struct page, but marked as reserved. Are we relying on the fact that NOMAP memory is also memblock_reserve()'d? > I am going to prepare the pfn_is_ram() change in addition to this > patch, but that should not be required for this fix to work correcly. > I don't think you need to bother with page_is_ram() then. The only place we use it is in devmem_is_allowed(), and there it makes sense to allow NOMAP regions to be accessed (provided that you think /dev/mem is a good idea in the first place). -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
