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Re: [PATCH v2 5/7] x86: extend do_mmu_update() to support returning the old PTE value
- To: Teddy Astie <teddy.astie@xxxxxxxxxx>, Kevin Lampis <kevin.lampis@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Fri, 11 Sep 2026 16:12:43 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, jbeulich@xxxxxxxx
- Delivery-date: Fri, 11 Sep 2026 15:13:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 11/09/2026 1:32 pm, Teddy Astie wrote:
> Le 10/09/2026 à 22:31, Kevin Lampis a écrit :
>> A new sub-op MMU_PT_UPDATE_SWAP when used will do an atomic swap to set
>> the new value and return the old PTE value through the req.val field.
>>
>> - The new PTE value in req.val must be 0, at the moment this is intended
>> for clearing only.
>>
>
> I'm not sure this is a good idea to restrict the feature for only 0.
> If in the future we want to expand this to non-0 values, we will need
> to advertise this property to the guest as well (so that it knows if
> non-0 values are supported). I don't know what supporting !0 would
> require (but it could be useful to get a idea of it).
Going further, this cannot be limited to 0 as an input, or to only L1e's.
What I don't see is why you need any restrictions at all ?
~Andrew
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