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Re: Design session notes: GPU acceleration in Xen
- To: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 17 Jun 2024 11:07:54 +0200
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- Cc: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, Ray Huang <ray.huang@xxxxxxx>, Xen developer discussion <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 17 Jun 2024 09:08:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 14.06.2024 18:44, Demi Marie Obenour wrote:
> On Fri, Jun 14, 2024 at 10:12:40AM +0200, Jan Beulich wrote:
>> On 14.06.2024 09:21, Roger Pau Monné wrote:
>>> I'm not sure it's possible to ensure that when using system RAM such
>>> memory comes from the guest rather than the host, as it would likely
>>> require some very intrusive hooks into the kernel logic, and
>>> negotiation with the guest to allocate the requested amount of
>>> memory and hand it over to dom0. If the maximum size of the buffer is
>>> known in advance maybe dom0 can negotiate with the guest to allocate
>>> such a region and grant it access to dom0 at driver attachment time.
>>
>> Besides the thought of transiently converting RAM to kind-of-MMIO, this
>> makes me think of another possible option: Could Dom0 transfer ownership
>> of the RAM that wants mapping in the guest (remotely resembling
>> grant-transfer)? Would require the guest to have ballooned down enough
>> first, of course. (In both cases it would certainly need working out how
>> the conversion / transfer back could be made work safely and reasonably
>> cleanly.)
>
> The kernel driver needs to be able to reclaim the memory at any time.
> My understanding is that this is used to migrate memory between VRAM and
> system RAM. It might also be used for other purposes.
Except: How would the kernel driver reclaim the memory when it's mapped
by a DomU?
Jan
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