From: Andy Lutomirski <luto@kernel.org>
To: Ankur Arora <ankur.a.arora@oracle.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Michal Hocko <mhocko@kernel.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
Arnd Bergmann <arnd@arndb.de>,
Andrew Morton <akpm@linux-foundation.org>,
Ira Weiny <ira.weiny@intel.com>,
linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH 5/8] x86/clear_page: add clear_page_uncached()
Date: Wed, 14 Oct 2020 08:45:37 -0700 [thread overview]
Message-ID: <CALCETrVKLv5DPByFcj7E5SBbv4mFt7mGQ9j-HU7G5u_aPGCYsQ@mail.gmail.com> (raw)
In-Reply-To: <20201014083300.19077-6-ankur.a.arora@oracle.com>
On Wed, Oct 14, 2020 at 1:33 AM Ankur Arora <ankur.a.arora@oracle.com> 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
next prev parent reply other threads:[~2020-10-14 15:45 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20201014083300.19077-1-ankur.a.arora@oracle.com>
2020-10-14 8:32 ` [PATCH 5/8] x86/clear_page: add clear_page_uncached() Ankur Arora
2020-10-14 15:45 ` Andy Lutomirski [this message]
2020-10-14 19:58 ` Borislav Petkov
2020-10-14 21:07 ` Andy Lutomirski
2020-10-14 21:12 ` Borislav Petkov
2020-10-15 3:37 ` Ankur Arora
2020-10-15 10:35 ` Borislav Petkov
2020-10-15 21:20 ` Ankur Arora
2020-10-16 18:21 ` Borislav Petkov
2020-10-15 3:21 ` Ankur Arora
2020-10-15 10:40 ` Borislav Petkov
2020-10-15 21:40 ` Ankur Arora
2020-10-14 20:54 ` Ankur Arora
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