Re: kern/57199 (Pure PVH i386 guests hang on disk activity)

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

> Date: Wed, 17 Jul 2024 01:15:12 +0200
> From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
> 
> On Tue, Jul 16, 2024 at 10:49:32PM +0000, riastradh%NetBSD.org@localhost wrote:
> > fixed in HEAD, needs pullup-10 and pullup-9
> 
> AFAIK it's not needed in netbsd-9, PVH is not supported before -10

Don't XEN3_DOM0 and XEN3_DOMU kernels have, e.g., xennet(4)?  If they
rely on xen_mb to enforce store-before-load ordering with respect to
the hypervisor (possibly on another physical CPU), they may need this
fix.

That said, by accident, it looks like this will only be relevant for
very old 32-bit x86 CPUs -- those without SSE2.  On CPUs with SSE2,
netbsd-9 hotpatches membar_sync to use MFENCE.  And all amd64 CPUs
have SSE2.