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Date: Wed, 14 Oct 2020 21:58:23 +0200 From: Borislav Petkov <bp@...en8.de> To: Andy Lutomirski <luto@...nel.org> Cc: Ankur Arora <ankur.a.arora@...cle.com>, LKML <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>, "Kirill A. Shutemov" <kirill@...temov.name>, Michal Hocko <mhocko@...nel.org>, Boris Ostrovsky <boris.ostrovsky@...cle.com>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>, Andrew Morton <akpm@...ux-foundation.org>, Ira Weiny <ira.weiny@...el.com>, linux-arch <linux-arch@...r.kernel.org> Subject: Re: [PATCH 5/8] x86/clear_page: add clear_page_uncached() On Wed, Oct 14, 2020 at 08:45:37AM -0700, Andy Lutomirski wrote: > On Wed, Oct 14, 2020 at 1:33 AM Ankur Arora <ankur.a.arora@...cle.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. Why does it have to be a separate call? Why isn't it behind the clear_page() alternative machinery so that the proper function is selected at boot? IOW, why does a user of clear_page functionality need to know at all about an "uncached" variant? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
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