[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] x86/IRQ: make internally used IRQs also honor the pending EOI stack
On 28.11.2019 12:39, Roger Pau Monné wrote: > On Thu, Nov 28, 2019 at 12:03:47PM +0100, Jan Beulich wrote: >> At the time the pending EOI stack was introduced there were no >> internally used IRQs which would have the LAPIC EOI issued from the >> ->end() hook. This had then changed with the introduction of IOMMUs, >> but the interaction issue was presumably masked by >> irq_guest_eoi_timer_fn() frequently EOI-ing interrupts way too early >> (which got fixed by 359cf6f8a0ec ["x86/IRQ: don't keep EOI timer >> running without need"]). >> >> The problem is that with us re-enabling interrupts across handler >> invocation, a higher priority (guest) interrupt may trigger while >> handling a lower priority (internal) one. The EOI issued from >> ->end() (for ACKTYPE_EOI kind interrupts) would then mistakenly >> EOI the higher priority (guest) interrupt, breaking (among other >> things) pending EOI stack logic's assumptions. > > Maybe there's something that I'm missing, but shouldn't hypervisor > vectors always be higher priority than guest ones? Depends - IOMMU ones imo aren't something that needs urgently dealing with, so a little bit of delay won't hurt. There would only be a problem if such interrupts could be deferred indefinitely. > I see there's already a range reserved for high priority vectors > ({FIRST/LAST}_HIPRIORITY_VECTOR), what's the reason for hypervisor > interrupts not using this range? We'd quickly run out of high priority vectors on systems with multiple (and perhaps indeed many) IOMMUs. > IMO it seems troublesome that pending guests vectors can delay the > injection of hypervisor interrupt vectors. As per above - depends. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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