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SubjectRe: [RFC PATCH v2 11/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW
On Tue, Jul 10, 2018 at 03:44:32PM -0700, Dave Hansen wrote:
> On 07/10/2018 03:26 PM, Yu-cheng Yu wrote:
> > + /*
> > + * On platforms before CET, other threads could race to
> > + * create a RO and _PAGE_DIRTY_HW PMD again. However,
> > + * on CET platforms, this is safe without a TLB flush.
> > + */
>
> If I didn't work for Intel, I'd wonder what the heck CET is and what the
> heck it has to do with _PAGE_DIRTY_HW. I think we need a better comment

And Changelog, the provided one is abysmal.

> than this. How about:
>
> Some processors can _start_ a write, but end up seeing
> a read-only PTE by the time they get to getting the
> Dirty bit. In this case, they will set the Dirty bit,
> leaving a read-only, Dirty PTE which looks like a Shadow
> Stack PTE.
>
> However, this behavior has been improved and will *not* occur on
> processors supporting Shadow Stacks. Without this guarantee, a
> transition to a non-present PTE and flush the TLB would be
> needed.

I'm still struggling. I think I get the first paragraph, but then what?

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