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Re: [PATCH v2 12/18] AMD/IOMMU: allow use of superpage mappings
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 13 Dec 2021 11:41:46 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Mon, 13 Dec 2021 10:42:07 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13.12.2021 11:33, Roger Pau Monné wrote:
> On Mon, Dec 13, 2021 at 11:00:23AM +0100, Jan Beulich wrote:
>> On 13.12.2021 10:45, Roger Pau Monné wrote:
>>> It would be better if we could somehow account this in a per-vCPU way,
>>> kind of similar to what we do with vPCI BAR mappings.
>>
>> But recording them per-vCPU wouldn't make any difference to the
>> number of pages that could accumulate in a single run. Maybe I'm
>> missing something in what you're thinking about here ...
>
> If Xen somehow did the free in guest vCPU context before resuming
> guest execution then you could yield when events are pending and thus
> allow other guests to run without hogging the pCPU, and the freeing
> would be accounted to vCPU sched slice time.
That's an interesting thought. Shouldn't be difficult to arrange for
HVM (from {svm,vmx}_vmenter_helper()), but I can't immediately see a
clean way of having the same for PV (short of an ad hoc call out of
assembly code somewhere after test_all_events).
Jan
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