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Re: [PATCH v2 07/18] x86/pv: update guest LDT mappings using the linear entries
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 14 Jan 2025 16:42:24 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 14 Jan 2025 15:42:30 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.01.2025 15:26, Roger Pau Monne wrote:
> The pv_map_ldt_shadow_page() and pv_destroy_ldt() functions rely on the L1
> table(s) that contain such mappings being stashed in the domain structure, and
> thus such mappings being modified by merely updating the require L1 entries.
>
> Switch pv_map_ldt_shadow_page() to unconditionally use the linear recursive,
> as
> that logic is always called while the vCPU is running on the current pCPU.
>
> For pv_destroy_ldt() use the linear mappings if the vCPU is the one currently
> running on the pCPU, otherwise use destroy_mappings().
>
> Note this requires keeping an array with the pages currently mapped at the LDT
> area, as that allows dropping the extra taken page reference when removing the
> mappings.
I'm confused by the wording of this paragraph: It reads as if you were
changing reference obtaining / dropping, yet it all looks to stay the
same. If I'm not mistaken you use the array to replace the acquiring of
the MFNs in question from the L1 page table entries. If so, I think it
would be nice if this could be described in a more direct way. Perhaps
first and foremost by replacing "allows" and getting rid of "extra".
Jan
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