linux-kernel - Re: [PATCH 6/6] x86: Fix stray A/D bit setting into non-present PTEs

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Message-ID: <CA+55aFwHGgiog+wFFDLXKjs4zVjMp-FLduGsEr800F5ruJ_aRA@mail.gmail.com>
Date:	Fri, 1 Jul 2016 09:25:01 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Hansen <dave@...1.net>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andi Kleen <ak@...ux.intel.com>,
	Michal Hocko <mhocko@...e.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 6/6] x86: Fix stray A/D bit setting into non-present PTEs

On Fri, Jul 1, 2016 at 9:14 AM, Dave Hansen <dave@...1.net> wrote:
>
> As I understand it, the erratum only affects a thread which is about to
> page fault.  The write associated with the dirty bit being set never
> actually gets executed.  So, the bit really *is* stray and isn't
> something we need to preserve.

Ok, good.

> Otherwise, we'd be really screwed because we couldn't ever simply clear it.

Oh, we could do the whole "clear the pte, then flush the tlb, then go
back and clear the stale dirty bits and move them into the backing
page".

I was afraid we might have to do something like that.

            Linus