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

[Dave Hansen]

On 07/01/2016 09:07 AM, Linus Torvalds wrote:
> But I also started worrying about us just losing sight of the dirty
> bit in particular. It's not enough that we ignore the dirty bit - we'd
> still want to make sure that the underlying backing page gets marked
> dirty, even if the CPU is buggy and ends doing it "delayed" after
> we've already unmapped the page.
> 
> So I get this feeling that we may need a fair chunk of your
> patch-series anyway.

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.

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