Re: [PATCH v2 4/6] mshv: limit SynIC management to MSHV-owned resources

[Jork Loeser]

On Mon, 6 Apr 2026, Anirudh Rayabharam wrote:

> On Fri, Apr 03, 2026 at 12:06:10PM -0700, Jork Loeser wrote:
> > The SynIC is shared between VMBus and MSHV. VMBus owns the message
> > page (SIMP), event flags page (SIEFP), global enable (SCONTROL),
> > and SINT2. MSHV adds SINT0, SINT5, and the event ring page (SIRBP).
> >
> > Currently mshv_synic_init() redundantly enables SIMP, SIEFP, and
>
> The redundant enable is probably a no-op from the hypervisor side so it
> probably doesn't hurt us. The main problem is with the tear down.

It's an MSR intercept. If we can replace this by an "if()" we shave a few 
cycles.

> An alternative approach could be: check if SIMP/SIEFP/SCONTROL is
> already enabled. If so, don't enable it again. If not enabled, enable it
> and keep track of what all stuf we have enabled. Then disable all of
> them during cleanup. This approach makes less assumptions about the
> behavior of the VMBUS driver and what stuff it does or doesn't use.

It would, yes. Then again, we drag yet more state and make debugging more 
complicated / less clear to reason what happens dynamically. I had been 
debating this briefly myself, and ultimately decided against it for that 
very reason.

Best,
Jork