On 1/9/25 4:25 PM, Tamas K Lengyel wrote:
On Thu, Jan 9, 2025 at 9:30 AM Oleksii Kurochko
<oleksii.kuroc...@gmail.com> wrote:
On 1/2/25 6:13 PM, Petr Beneš wrote:
From: Petr Beneš <w1be...@gmail.com>
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
<ta...@tklengyel.com>" 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.
In this case, I believe we should consider including it in the current
release, as it was technically ready for merging before the Feature
Freeze deadline.
I would like to kindly ask the x86 maintainers for clarification on why
this patch series was not merged.
~ Oleksii
