On 2020-10-14 8:45 a.m., Andy Lutomirski wrote:
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.
Yeah, these are a lot more obvious. Thanks. Will fix.
Ankur
--Andy
