On 11/07/2016 03:31 PM, Naoya Horiguchi wrote: > pmd_present() checks _PAGE_PSE along with _PAGE_PRESENT to avoid false > negative > return when it races with thp spilt (during which _PAGE_PRESENT is temporary > cleared.) I don't think that dropping _PAGE_PSE check in pmd_present() works > well because it can hurt optimization of tlb handling in thp split. > In the current kernel, bit 6 is not used in non-present format because > nonlinear > file mapping is obsolete, so let's move _PAGE_SWP_SOFT_DIRTY to that bit. > Bit 7 is used as reserved (always clear), so please don't use it for other > purpose. ... > #ifdef CONFIG_MEM_SOFT_DIRTY > -#define _PAGE_SWP_SOFT_DIRTY _PAGE_PSE > +#define _PAGE_SWP_SOFT_DIRTY _PAGE_DIRTY > #else > #define _PAGE_SWP_SOFT_DIRTY (_AT(pteval_t, 0)) > #endif
I'm not sure this works. Take a look at commit 00839ee3b29 and the erratum it works around. I _think_ this means that a system affected by the erratum might see an erroneous _PAGE_SWP_SOFT_DIRTY/_PAGE_DIRTY get set in swap ptes. There are much worse things that can happen, but I don't think bits 5 (Accessed) and 6 (Dirty) are good choices since they're affected by the erratum.
