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Re: [PATCH v3.1 2/2] x86/amd: Enable TCE in Xen
- To: Teddy Astie <teddy.astie@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 9 Apr 2025 10:11:32 +0200
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- Cc: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Community Manager <community.manager@xxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 09 Apr 2025 08:11:47 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 09.04.2025 09:11, Jan Beulich wrote:
> On 07.04.2025 11:10, Teddy Astie wrote:
>> Aside exposing this flag to guests, Xen can also make use of it to reduce
>> the cost of
>> some TLB flushes. Enable this flag if supported by hardware.
>
> As said before: This needs to come with (perhaps a lot of) justification as
> to it being safe for Xen to use without any adjustments anywhere else. This
> exercise may not be left to the reviewer(s).
One case to consider in particular is a shadow guest (EFER.TCE clear as per
patch 1) running with host EFER.TCE set. The TLB flushes we do may then simply
be insufficient for the guest's expectations.
Jan
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