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SubjectRe: [RFC PATCH v2 11/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW
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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
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.


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