Re: [PATCH v3 0/2] x86: Add Support for Paging-Write Feature

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, Jan 9, 2025 at 9:30 AM Oleksii Kurochko
<oleksii.kurochko@xxxxxxxxx> wrote:
>
>
> On 1/2/25 6:13 PM, Petr Beneš wrote:
>
> From: Petr Beneš <w1benny@xxxxxxxxx>
>
> Changes since v2:
> - Reset entry->pw in all cases in p2m_set_entry, except for p2m_access_r_pw
>
> Changes since v1:
> - Added signed-off-by tags
>
> This patch introduces a new XENMEM_access_r_pw permission. Functionally, it 
> is similar to XENMEM_access_r, but for processors with 
> TERTIARY_EXEC_EPT_PAGING_WRITE support (Intel 12th Gen/Alder Lake and later), 
> it also permits the CPU to write to the page during guest page-table walks 
> (e.g., updating A/D bits) without triggering an EPT violation.
>
> This behavior works by both enabling the EPT paging-write feature and setting 
> the EPT paging-write flag in the EPT leaf entry.
>
> This feature provides a significant performance boost for introspection tools 
> that monitor guest page-table updates. Previously, every page-table 
> modification by the guest—including routine updates like setting A/D 
> bits—triggered an EPT violation, adding unnecessary overhead. The new 
> XENMEM_access_r_pw permission allows these "uninteresting" updates to occur 
> without EPT violations, improving efficiency.
>
> Considering that this feature provides a significant performance boost for 
> introspection tools probably we could consider to take it to current release.
>
> I see that the patch series was acked-by "Acked-by: Tamas K Lengyel 
> <tamas@xxxxxxxxxxxxx>" but based on the change log it is not clear when 
> exactly
>
> before Feature freeze date or not. ( and I don't see any reply from Tamas ).

I've acked the patch Thu, Dec 19, 2024.

Cheers,
Tamas