Re: [RFC PATCH v3 12/24] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW

[Dave Hansen]

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 â 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.