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Re: [PATCH v4 1/7] xen/evtchn: Make sure all buckets below d->valid_evtchns are allocated
- To: Rahul Singh <rahul.singh@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 6 Sep 2022 15:45:56 +0200
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- Cc: Julien Grall <jgrall@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 06 Sep 2022 13:46:08 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 06.09.2022 15:40, Rahul Singh wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
>
> Since commit 01280dc19cf3 "evtchn: simplify port_is_valid()", the event
> channels code assumes that all the buckets below d->valid_evtchns are
> always allocated.
>
> This assumption hold in most of the situation because a guest is not
> allowed to chose the port. Instead, it will be the first free from port
> 0.
>
> When static event channel support will be added for dom0less domains
> user can request to allocate the evtchn port numbers that are scattered
> in nature.
>
> The existing implementation of evtchn_allocate_port() is not able to
> deal with such situation and will end up to override bucket or/and leave
> some bucket unallocated. The latter will result to a droplet crash if
> the event channel belongs to an unallocated bucket.
>
> This can be solved by making sure that all the buckets below
> d->valid_evtchns are allocated. There should be no impact for most of
> the situation but LM/LU as only one bucket would be allocated. For
> LM/LU, we may end up to allocate multiple buckets if ports in use are
> sparse.
>
> A potential alternative is to check that the bucket is valid in
> is_port_valid(). This should still possible to do it without taking
> per-domain lock but will result a couple more of memory access.
>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
> Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
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