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Re: [PATCH v6 3/6] xen/arm: ffa: Introduce VM to VM support
- To: Julien Grall <julien@xxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Wed, 16 Jul 2025 06:22:19 +0000
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "jens.wiklander@xxxxxxxxxx" <jens.wiklander@xxxxxxxxxx>, Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>
- Delivery-date: Wed, 16 Jul 2025 06:23:17 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Nodisclaimer: true
- Thread-index: AQHbyyty9jTfyAQcDUecgzUaHU35fLPrtYWAgEjoDQA=
- Thread-topic: [PATCH v6 3/6] xen/arm: ffa: Introduce VM to VM support
Hi Julien,
Sorry for the very long delay.
> On 30 May 2025, at 23:00, Julien Grall <julien@xxxxxxx> wrote:
>
> Hi Bertrand,
>
> On 22/05/2025 16:08, Bertrand Marquis wrote:
>> diff --git a/xen/arch/arm/tee/ffa_partinfo.c
>> b/xen/arch/arm/tee/ffa_partinfo.c
>> index dfa0b23eaf38..66ea1860e97a 100644
>> --- a/xen/arch/arm/tee/ffa_partinfo.c
>> +++ b/xen/arch/arm/tee/ffa_partinfo.c
>> @@ -150,6 +150,67 @@ out:
>> return ret;
>> }
>> +static int32_t ffa_get_vm_partinfo(uint32_t *vm_count, void *dst_buf,
>> + void *end_buf, uint32_t dst_size)
>> +{
>> + struct ffa_ctx *curr_ctx = current->domain->arch.tee;
>> + struct ffa_ctx *dest_ctx, *tmp;
>> + uint32_t count = 0;
>> +
>> + /*
>> + * There could potentially be a lot of VMs in the system and we could
>> + * hold the CPU for long here.
>> + * Right now there is no solution in FF-A specification to split
>> + * the work in this case.
>> + * TODO: Check how we could delay the work or have preemption checks.
>> + */
>> + list_for_each_entry_safe(dest_ctx, tmp, &ffa_ctx_head, ctx_list)
>
> Looking at this code again, I am a bit puzzled why we don't seem to take any
> lock and use list_for_each_entry_safe().
>
> I was under the impression that list_for_each_entry_safe() is used if we
> delete an entry within the loop. But it is not used to protect against a
> deletion from another core.
Yes you are right, my logic here is wrong.
>
> Did I misunderstand the logic? If not, we possibly want to use a readlock
> (over the existing spinlock).
Definitely yes, thanks a lot for the review.
I will fix that in v7 by protecting the list using a read lock.
Cheers
Bertrand
>
> Cheers,
>
> --
> Julien Grall
>
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