Re: [RFC PATCH v4 20/21] iommu/vt-d: hpet: Reserve an interrupt remampping table entry for watchdog

From: Thomas Gleixner
Date: Sat Jun 22 2019 - 03:23:13 EST

On Fri, 21 Jun 2019, Ricardo Neri wrote:
> On Fri, Jun 21, 2019 at 10:05:01PM +0200, Thomas Gleixner wrote:
> > On Fri, 21 Jun 2019, Jacob Pan wrote:
> > > >
> > > I looked at the code again, seems the per cpu HPET code already taken
> > > care of HPET MSI management. Why can't we use IR-HPET-MSI chip and
> > > domain to allocate and set affinity etc.?
> > > Most APIC timer has ARAT not enough per cpu HPET, so per cpu HPET is
> > > not used mostly.
> >
> > Sure, we can use that, but that does not allow to move the affinity from
> > NMI context either. Same issue with the IOMMU as with the other hack.
> If I understand Thomas' point correctly, the problem is having to take
> lock in NMI context to update the IRTE for the HPET; both as in my hack
> and in the generic irq code. The problem is worse when using the generic
> irq code as there are several layers and several locks that need to be
> handled.

It does not matter how many locks are involved. One is enough to wedge the