On Tue, 2015-07-21 at 10:05 +0200, Ingo Molnar wrote: > * Toshi Kani <toshi.kani@xxxxxx> wrote: > > > The PAT bit gets relocated to bit 12 when PUD and PMD mappings are > > used. > > This bit 12, however, is not covered by PTE_FLAGS_MASK, which is > > corrently > > used for masking pfn and flags for all cases. > > > > Patch 1/4-2/4 make changes necessary for patch 3/4 to use > > P?D_PAGE_MASK. > > > > Patch 3/4 fixes pud/pmd interfaces to handle the PAT bit when PUD and > > PMD > > mappings are used. > > > > Patch 3/4 fixes /sys/kernel/debug/kernel_page_tables to show the PAT > > bit > > properly. > > > > Note, the PAT bit is first enabled in 4.2-rc1 with WT mappings. > > Are patches 1-3 only needed to fix /sys/kernel/debug/kernel_page_tables > output, or > are there other things fixed as well? The patches do not tell us any of > that information ... Patch 3 (and patch 1-2 needed for patch 3) fixes multiple pud/pmd interfaces to work properly with _PAGE_PAT_LARGE bit set. Because pmem is the only module that can create a range with this bit set with large page WT maps in 4.2, this issue has not been exposed other than the case in kernel_page_tables fixed by patch 4. Since there can be other cases in future, all patches should go to 4.2 to prevent them to happen. There is no issue in 4.1 & older since they cannot set the bit. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>