Re: [PATCH v3 1/2] system/memory: Use qemu_ram_{copy, move}() in ram device region accessors

On 7/22/26 2:27 AM, Peter Xu wrote:
> On Tue, Jul 21, 2026 at 03:37:53PM +1000, Gavin Shan wrote:
>> If Peter is fine with two variants for x86 and non-x86 architectures.
>> I can post (v4) for further review. That will be something like below
>> and let me know if there are any other improvements are needed.
> 
> I have a generic question on the "unaligned access for x86": I think the
> question is about the one Michael raised here on unaligned access may break
> x86 here:
> 
>    https://lore.kernel.org/qemu-devel/[email protected]/
> 
>    3. (theoretical concern) also on x86, unaligned accesses are
>    possible on guest and host, so converting an unaligned access to a
>    series of aligned ones can in theory break devices.
> 
> Is that a real problem we need to consider, or can we start with unified
> approach and leave it for later?
> 

I'm leaving this question to Michael.

> PS: I apologize if I missed important piece of info along the way; I didn't
> follow closely on the discussion on this topic in the past few weeks.
> 
> One thing to mention is, what we change should only need to affect
> ram_device, AFAIU.. so most memcpy()/memmove() shouldn't be changed for any
> arch when it's pure RAM.
> 

It depends. This patch intends to fix issue [1] in the lower layer by using
the newly added accessors (qemu_ram_{copy, move}) on all directly accessible
regions including the regular (pure) RAM region. Otherwise, the newly added
accessors should be limited to ram_device regions only as you said.

[1] https://lore.kernel.org/qemu-devel/[email protected]/

Thanks,
Gavin