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Re: [PATCH] x86/pv: limit GDT and LDT mappings areas to max number of vCPUs
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 21 Nov 2024 12:32:11 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 21 Nov 2024 11:32:25 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21.11.2024 12:12, Roger Pau Monne wrote:
> The allocation of the paging structures in the per-domain area for mapping the
> guest GDT and LDT can be limited to the maximum number of vCPUs the guest can
> have. The maximum number of vCPUs is available at domain creation since
> commit
> 4737fa52ce86.
>
> Limiting to the actual number of vCPUs avoids wasting memory for paging
> structures that will never be used. Current logic unconditionally uses 513
> pages, one page for the L3, plus 512 L1 pages. For guests with equal or less
> than 16 vCPUs only 2 pages are used (each guest vCPU GDT/LDT can only consume
> 32 L1 slots).
>
> No functional change intended, all possible domain vCPUs should have the GDT
> and LDT paging structures allocated and setup at domain creation, just like
> before the change.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
perhaps with the small adjustment Andrew has asked for.
Jan
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