Re: Emulating CPUs with larger atomic accesses

[Richard Henderson]

On 5/24/22 02:27, Florian Weimer wrote:
> * Richard Henderson:
>
> > On 5/13/22 03:00, Florian Weimer wrote:
> > > What's QEMU's approach to emulating CPU instructions that atomatically
> > > operate on values larger than what is supported by the host CPU?
> > > I assume that for full system emulation, this is not a problem, but
> > > qemu-user will not achieve atomic behavior on shared memory mappings.
> > > How much of a problem is this in practice?
> >
> > Well, it doesn't work, no.  In practice, x86_64 supports 128-bit
> > atomic operations, and guest requires more than that.  No one really
> > cares anymore about 32-bit hosts with smaller atomic operations.
>
> Which part doesn't work?  Full-system emulation?

No, user-only.

> Do guests really require wider-than-128 atomics?  That's quite
> surprising?

Typo there -- "and no guest requires...".


r~