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Date: Thu, 15 Oct 2020 14:40:06 -0700 From: Ankur Arora <ankur.a.arora@...cle.com> To: Borislav Petkov <bp@...en8.de> Cc: Andy Lutomirski <luto@...capital.net>, Andy Lutomirski <luto@...nel.org>, 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 2020-10-15 3:40 a.m., Borislav Petkov wrote: > On Wed, Oct 14, 2020 at 08:21:57PM -0700, Ankur Arora wrote: >> Also, if we did extend clear_page() to take the page-size as parameter >> we still might not have enough information (ex. a 4K or a 2MB page that >> clear_page() sees could be part of a GUP of a much larger extent) to >> decide whether to go uncached or not. > > clear_page* assumes 4K. All of the lowlevel asm variants do. So adding > the size there won't bring you a whole lot. > > So you'd need to devise this whole thing differently. Perhaps have a > clear_pages() helper which decides based on size what to do: uncached > clearing or the clear_page() as is now in a loop. I think that'll work well for GB pages, where the clear_pages() helper has enough information to make a decision. But, unless I'm missing something, I'm not sure how that would work for say, a 1GB mm_populate() using 4K pages. The clear_page() (or clear_pages()) in that case would only see the 4K size. But let me think about this more (and look at the callsites as you suggest.) > > Looking at the callsites would give you a better idea I'd say. Thanks, yeah that's a good idea. Let me go do that. Ankur > > Thx. >
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