On Wed, Oct 14, 2020 at 1:33 AM Ankur Arora <ankur.a.arora@xxxxxxxxxx> wrote: > > Define clear_page_uncached() as an alternative_call() to clear_page_nt() > if the CPU sets X86_FEATURE_NT_GOOD and fallback to clear_page() if it > doesn't. > > Similarly define clear_page_uncached_flush() which provides an SFENCE > if the CPU sets X86_FEATURE_NT_GOOD. As long as you keep "NT" or "MOVNTI" in the names and keep functions in arch/x86, I think it's reasonable to expect that callers understand that MOVNTI has bizarre memory ordering rules. But once you give something a generic name like "clear_page_uncached" and stick it in generic code, I think the semantics should be more obvious. How about: clear_page_uncached_unordered() or clear_page_uncached_incoherent() and flush_after_clear_page_uncached() After all, a naive reader might expect "uncached" to imply "caches are off and this is coherent with everything". And the results of getting this wrong will be subtle and possibly hard-to-reproduce corruption. --Andy
