On 15/07/2019 09:11, Alexey Kardashevskiy wrote: > There is a race between releasing an irq on one cpu and fetching it > from XIVE on another cpu as there does not seem to be any locking between > these, probably because xive_irq_chip::irq_shutdown() is supposed to > remove the irq from all queues in the system which it does not do. > > As a result, when such released irq appears in a queue, we take it > from the queue but we do not change the current priority on that cpu and > since there is no handler for the irq, EOI is never called and the cpu > current priority remains elevated (7 vs. 0xff==unmasked). If another irq > is assigned to the same cpu, then that device stops working until irq > is moved to another cpu or the device is reset. > > This adds a new ppc_md.orphan_irq callback which is called if no irq > descriptor is found. The XIVE implementation drops the current priority > to 0xff which effectively unmasks interrupts in a current CPU.
The test on generic_handle_irq() catches interrupt events that were served on a target CPU while the source interrupt was being shutdown on another CPU. The orphan_irq() handler restores the CPPR in such cases. This looks OK to me. I would have added some more comments in the code. Reviewed-by: Cédric Le Goater <c...@kaod.org> And adding to the list of future cleanups : a 'set_cppr' helper. Thanks, C. > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > --- > Changes: > v2: > * added ppc_md.orphan_irq > > --- > > Found it on P9 system with: > - a host with 8 cpus online > - a boot disk on ahci with its msix on cpu#0 > - a guest with 2xGPUs + 6xNVLink + 4 cpus > - GPU#0 from the guest is bound to the same cpu#0. > > Killing a guest killed ahci and therefore the host because of the race. > Note that VFIO masks interrupts first and only then resets the device. > --- > arch/powerpc/include/asm/machdep.h | 3 +++ > arch/powerpc/kernel/irq.c | 9 ++++++--- > arch/powerpc/sysdev/xive/common.c | 10 ++++++++++ > 3 files changed, 19 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/include/asm/machdep.h > b/arch/powerpc/include/asm/machdep.h > index c43d6eca9edd..6cc14e28e89a 100644 > --- a/arch/powerpc/include/asm/machdep.h > +++ b/arch/powerpc/include/asm/machdep.h > @@ -59,6 +59,9 @@ struct machdep_calls { > /* Return an irq, or 0 to indicate there are none pending. */ > unsigned int (*get_irq)(void); > > + /* Drops irq if it does not have a valid descriptor */ > + void (*orphan_irq)(unsigned int irq); > + > /* PCI stuff */ > /* Called after allocating resources */ > void (*pcibios_fixup)(void); > diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c > index bc68c53af67c..b4e06d05bdba 100644 > --- a/arch/powerpc/kernel/irq.c > +++ b/arch/powerpc/kernel/irq.c > @@ -632,10 +632,13 @@ void __do_irq(struct pt_regs *regs) > may_hard_irq_enable(); > > /* And finally process it */ > - if (unlikely(!irq)) > + if (unlikely(!irq)) { > __this_cpu_inc(irq_stat.spurious_irqs); > - else > - generic_handle_irq(irq); > + } else if (generic_handle_irq(irq)) { > + if (ppc_md.orphan_irq) > + ppc_md.orphan_irq(irq); > + __this_cpu_inc(irq_stat.spurious_irqs); > + } > > trace_irq_exit(regs); > > diff --git a/arch/powerpc/sysdev/xive/common.c > b/arch/powerpc/sysdev/xive/common.c > index 082c7e1c20f0..b4054091999a 100644 > --- a/arch/powerpc/sysdev/xive/common.c > +++ b/arch/powerpc/sysdev/xive/common.c > @@ -283,6 +283,15 @@ static unsigned int xive_get_irq(void) > return irq; > } > > +static void xive_orphan_irq(unsigned int irq) > +{ > + struct xive_cpu *xc = __this_cpu_read(xive_cpu); > + > + xc->cppr = 0xff; > + out_8(xive_tima + xive_tima_offset + TM_CPPR, 0xff); > + DBG_VERBOSE("orphan_irq: irq %d, adjusting CPPR to 0xff\n", irq); > +} > + > /* > * After EOI'ing an interrupt, we need to re-check the queue > * to see if another interrupt is pending since multiple > @@ -1419,6 +1428,7 @@ bool __init xive_core_init(const struct xive_ops *ops, > void __iomem *area, u32 o > xive_irq_priority = max_prio; > > ppc_md.get_irq = xive_get_irq; > + ppc_md.orphan_irq = xive_orphan_irq; > __xive_enabled = true; > > pr_devel("Initializing host..\n"); >