KVM/QEMU community call tomorrow - agenda items?

KVM/QEMU community call tomorrow - agenda items?

[Alex Bennée]

Hi,

The KVM/QEMU community call is at:

https://meet.jit.si/kvmcallmeeting
@
01/09/2026 14:00 UTC

Are there any agenda items for the sync-up?

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro

Re: KVM/QEMU community call tomorrow - agenda items?

[Philippe Mathieu-Daudé]

On 31/8/26 09:24, Alex Bennée wrote:
> 
> Hi,
> 
> The KVM/QEMU community call is at:
> 
> https://meet.jit.si/kvmcallmeeting
> @
> 01/09/2026 14:00 UTC
> 
> Are there any agenda items for the sync-up?

Mark suggested 2 topics but I can only remember one of them:

- How to merge a series what touch many subsystems and which is
   mostly reviewed but few maintainers are not responding

Maybe the other one is about merging experiments?

Re: KVM/QEMU community call tomorrow - agenda items?

[BillXiang]

On 8/31/2026 3:24 PM, Alex Bennée wrote:
> 
> Hi,
> 
> The KVM/QEMU community call is at:
> 
> https://meet.jit.si/kvmcallmeeting
> @
> 01/09/2026 14:00 UTC
> 
> Are there any agenda items for the sync-up?
> 

Hi,

How about discussing the patch[1]:
"virtio: Add aligned ld/st accessors for vring".

As pointed out in the patch, this has been a long-standing issue. It is 
now necessary to introduce atomic accessors for fields that require 
atomicity, such as the avail_idx field in virtio. This support is 
especially crucial for architectures like RISC-V, which do not natively 
support misaligned memory accesses.

I'm particularly eager to receive more suggestions for it.

Thanks,
--
BillXiang

[1] 
https://lore.kernel.org/qemu-devel/20260821100856.1794011-1-xiangwencheng@lanxincomputing.com/

Re: KVM/QEMU community call tomorrow - agenda items?

[Philippe Mathieu-Daudé]

On 31/8/26 13:49, BillXiang wrote:

> How about discussing the patch[1]:
> "virtio: Add aligned ld/st accessors for vring".
> 
> As pointed out in the patch, this has been a long-standing issue. It is
> now necessary to introduce atomic accessors for fields that require
> atomicity, such as the avail_idx field in virtio. This support is
> especially crucial for architectures like RISC-V, which do not natively
> support misaligned memory accesses.
> 
> I'm particularly eager to receive more suggestions for it.

This is a very technical topic, not sure if the community call will
be a better place than the mailing list, in particular if no virtio /
atomic expert developers appears. We'll see :)

Re: KVM/QEMU community call tomorrow - agenda items?

[Peter Xu]

On Mon, Aug 31, 2026 at 05:46:12PM +0200, Philippe Mathieu-Daudé wrote:
> On 31/8/26 13:49, BillXiang wrote:
> 
> > How about discussing the patch[1]:
> > "virtio: Add aligned ld/st accessors for vring".
> > 
> > As pointed out in the patch, this has been a long-standing issue. It is
> > now necessary to introduce atomic accessors for fields that require
> > atomicity, such as the avail_idx field in virtio. This support is
> > especially crucial for architectures like RISC-V, which do not natively
> > support misaligned memory accesses.
> > 
> > I'm particularly eager to receive more suggestions for it.

I saw the last email was from me..

https://lore.kernel.org/qemu-devel/aoxiBB2Wn8NiL5s6@x1.local/

I believe that was what PeterM suggested. I think Richard also at least
partly agrees. so I thought we had at least partial consensus on the rough
idea, if not exactly how.

I confess I haven't fully got the latter part of Richard's comment,
regarding the possibility to reuse accel/tcg/ldst_atomicity.c.inc: that
path seems to invole a guest CPU context, where in the case of reading
virtio ring it is from host and it has no guest CPU context.  But I think
we can continue the discussion on the list in that thread.

> 
> This is a very technical topic, not sure if the community call will
> be a better place than the mailing list, in particular if no virtio /
> atomic expert developers appears. We'll see :)

Yes, I had such similar feeling that the problem was not yet blocked by
something that a video call would better help..

For example, I still want to double check if that change would work for
your current use case, it will at least verify the thought, no matter if we
want to use it or not.

Thanks,

-- 
Peter Xu

Re: KVM/QEMU community call tomorrow - agenda items?

[BillXiang]

On 8/31/2026 11:46 PM, Philippe Mathieu-Daudé wrote:
> On 31/8/26 13:49, BillXiang wrote:
> 
>> How about discussing the patch[1]:
>> "virtio: Add aligned ld/st accessors for vring".
>>
>> As pointed out in the patch, this has been a long-standing issue. It is
>> now necessary to introduce atomic accessors for fields that require
>> atomicity, such as the avail_idx field in virtio. This support is
>> especially crucial for architectures like RISC-V, which do not natively
>> support misaligned memory accesses.
>>
>> I'm particularly eager to receive more suggestions for it.
> 
> This is a very technical topic, not sure if the community call will
> be a better place than the mailing list, in particular if no virtio /
> atomic expert developers appears. We'll see :)

Sorry, I'm not yet familiar with the community call process. If this 
isn't for technical topic, please feel free to disregard my message.

BTY, this patch isn't limited to virtio. The load/store functions are 
intended to handle various use cases across different architectures. 
This might also serve as a good example for Philippe's topic: "How to 
merge a series that touches many subsystems, with most reviews already 
done but a few maintainers still not responding."

Thanks,
--
BillXiang

Re: KVM/QEMU community call tomorrow - agenda items?

[BillXiang]

On 9/1/2026 1:05 AM, Peter Xu wrote:
> On Mon, Aug 31, 2026 at 05:46:12PM +0200, Philippe Mathieu-Daudé wrote:
>> On 31/8/26 13:49, BillXiang wrote:
>>
>>> How about discussing the patch[1]:
>>> "virtio: Add aligned ld/st accessors for vring".
>>>
>>> As pointed out in the patch, this has been a long-standing issue. It is
>>> now necessary to introduce atomic accessors for fields that require
>>> atomicity, such as the avail_idx field in virtio. This support is
>>> especially crucial for architectures like RISC-V, which do not natively
>>> support misaligned memory accesses.
>>>
>>> I'm particularly eager to receive more suggestions for it.
> 
> I saw the last email was from me..
> 
> https://lore.kernel.org/qemu-devel/aoxiBB2Wn8NiL5s6@x1.local/
> 
> I believe that was what PeterM suggested. I think Richard also at least
> partly agrees. so I thought we had at least partial consensus on the rough
> idea, if not exactly how.
> 
> I confess I haven't fully got the latter part of Richard's comment,
> regarding the possibility to reuse accel/tcg/ldst_atomicity.c.inc: that
> path seems to invole a guest CPU context, where in the case of reading
> virtio ring it is from host and it has no guest CPU context.  But I think
> we can continue the discussion on the list in that thread.
> 
>>
>> This is a very technical topic, not sure if the community call will
>> be a better place than the mailing list, in particular if no virtio /
>> atomic expert developers appears. We'll see :)
> 
> Yes, I had such similar feeling that the problem was not yet blocked by
> something that a video call would better help..
> 
> For example, I still want to double check if that change would work for
> your current use case, it will at least verify the thought, no matter if we
> want to use it or not.
> 
> Thanks,
> 

Thanks for your reply. Your change works for the virtio use case. While 
waiting for further comments, I've also gathered some additional 
information. Let's continue the discussion on the original thread.

--
BillXiang

Re: KVM/QEMU community call tomorrow - agenda items?

[Markus Armbruster]

"BillXiang" <xiangwencheng@lanxincomputing.com> writes:

> On 8/31/2026 11:46 PM, Philippe Mathieu-Daudé wrote:
>> On 31/8/26 13:49, BillXiang wrote:
>> 
>>> How about discussing the patch[1]:
>>> "virtio: Add aligned ld/st accessors for vring".
>>>
>>> As pointed out in the patch, this has been a long-standing issue. It is
>>> now necessary to introduce atomic accessors for fields that require
>>> atomicity, such as the avail_idx field in virtio. This support is
>>> especially crucial for architectures like RISC-V, which do not natively
>>> support misaligned memory accesses.
>>>
>>> I'm particularly eager to receive more suggestions for it.
>> 
>> This is a very technical topic, not sure if the community call will
>> be a better place than the mailing list, in particular if no virtio /
>> atomic expert developers appears. We'll see :)
>
> Sorry, I'm not yet familiar with the community call process. If this 
> isn't for technical topic, please feel free to disregard my message.

The technical conversation with reviewers starts on the mailing list,
where it's asynchronous, public, and archived.

Occasionally, this gets stuck in ways that a call can resolve best.  The
community call is an option then.  Make sure that the right people
attend.  Do consider scheduling a separate call instead, to not bore the
"wrong" people on the community call.

[...]

Re: KVM/QEMU community call tomorrow - agenda items?

[Mark Cave-Ayland]

On 31/08/2026 11:12, Philippe Mathieu-Daudé wrote:

> On 31/8/26 09:24, Alex Bennée wrote:
>>
>> Hi,
>>
>> The KVM/QEMU community call is at:
>>
>> https://urldefense.proofpoint.com/v2/url? 
>> u=https-3A__meet.jit.si_kvmcallmeeting&d=DwIDaQ&c=s883GpUCOChKOHiocYtGcg&r=c23RpsaH4D2MKyD3EPJTDa0BAxz6tV8aUJqVSoytEiY&m=tJnw3gip-5JC7hYEXkI3jFOeCB5tdEvEhf7cFH-iTEakJq0k9z98tMYtI1pEpyUD&s=V9nPukf4EkuZhKo4vCepVa5Swiw6ejdGfdC3itPL_XU&e= @
>> 01/09/2026 14:00 UTC
>>
>> Are there any agenda items for the sync-up?
> 
> Mark suggested 2 topics but I can only remember one of them:
> 
> - How to merge a series what touch many subsystems and which is
>    mostly reviewed but few maintainers are not responding

Yes, I'm happy to talk about this on the call :)

> Maybe the other one is about merging experiments?

I'm not sure, but I really wish I could remember!


ATB,

Mark.