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SubjectRe: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW
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On 08/31/2018 10:46 AM, Andy Lutomirski wrote:
> On Thu, Aug 30, 2018 at 11:55 AM, Dave Hansen
>> That little hunk will definitely need to get updated with something like:
>>
>> On processors enumerating support for CET, the processor will on
>> set the dirty flag on paging structure entries in which the W
>> flag is 1.
>
> Can we get something much stronger, perhaps? Like this:
>
> On processors enumerating support for CET, the processor will write to
> the accessed and/or dirty flags atomically, as if using the LOCK
> CMPXCHG instruction. The memory access, any cached entries in any
> paging-structure caches, and the values in the paging-structure entry
> before and after writing the A and/or D bits will all be consistent.

There's some talk of this already in: 8.1.2.1 Automatic Locking:

> When updating page-directory and page-table entries — When updating
> page-directory and page-table entries, the processor uses locked
> cycles to set the accessed and dirty flag in the page-directory and
> page-table entries.
As for the A/D consistency, I'll see if I can share that before it hits
the SDM for real and see if it's sufficient for everybody.

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