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Re: [PATCH] x86/altp2m: p2m_altp2m_get_or_propagate() should honor ap2m->default_access
- To: Petr Beneš <w1benny@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 14 Feb 2024 18:14:59 +0000
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- Cc: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>, Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>, Petre Pircalabu <ppircalabu@xxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 14 Feb 2024 18:15:21 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06/02/2024 10:08 am, Petr Beneš wrote:
> From: Petr Beneš <w1benny@xxxxxxxxx>
>
> This patch addresses a behavior discrepancy in the handling of altp2m views,
> where upon the creation and subsequent EPT violation, the page access
> permissions were incorrectly inherited from the hostp2m instead of respecting
> the altp2m default_access.
>
> Previously, when a new altp2m view was established with restrictive
> default_access permissions and activated via xc_altp2m_switch_to_view(),
> it failed to trigger an event on the first access violation. This behavior
> diverged from the intended mechanism, where the altp2m's default_access
> should dictate the initial permissions, ensuring proper event triggering on
> access violations.
>
> The correction involves modifying the handling mechanism to respect the
> altp2m view's default_access upon its activation, eliminating the need for
> setting memory access permissions for the entire altp2m range (e.g. within
> xen-access.c). This change not only aligns the behavior with the expected
> access control logic but also results in a significant performance improvement
> by reducing the overhead associated with setting memory access permissions
> across the altp2m range.
>
> Signed-off-by: Petr Beneš <w1benny@xxxxxxxxx>
It appears that all discussion has completed.
So unless anyone screams, I'm going to commit this with Tamas' ack as
he's the major user of this functionality.
~Andrew
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