[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] xen/arm: Handle platforms with edge-triggered virtual timer
Hi Ian, On 02/12/14 13:54, Ian Campbell wrote: > On Fri, 2014-11-28 at 15:17 +0000, Julien Grall wrote: >> Some platforms (such as Xgene and ARMv8 models) use an edge-triggered >> interrupt >> for the virtual timer. Even if the timer output signal is masked in the >> context switch, the GIC will keep track that of any interrupts raised >> while IRQs are disabled. As soon as IRQs are re-enabled, the virtual >> interrupt timer will be injected to Xen. >> >> If an idle vVCPU was scheduled next then the interrupt handler doesn't >> expect to the receive the IRQ and will crash: >> >> (XEN) [<0000000000228388>] _spin_lock_irqsave+0x28/0x94 (PC) >> (XEN) [<0000000000228380>] _spin_lock_irqsave+0x20/0x94 (LR) >> (XEN) [<0000000000250510>] vgic_vcpu_inject_irq+0x40/0x1b0 >> (XEN) [<000000000024bcd0>] vtimer_interrupt+0x4c/0x54 >> (XEN) [<0000000000247010>] do_IRQ+0x1a4/0x220 >> (XEN) [<0000000000244864>] gic_interrupt+0x50/0xec >> (XEN) [<000000000024fbac>] do_trap_irq+0x20/0x2c >> (XEN) [<0000000000255240>] hyp_irq+0x5c/0x60 >> (XEN) [<0000000000241084>] context_switch+0xb8/0xc4 >> (XEN) [<000000000022482c>] schedule+0x684/0x6d0 >> (XEN) [<000000000022785c>] __do_softirq+0xcc/0xe8 >> (XEN) [<00000000002278d4>] do_softirq+0x14/0x1c >> (XEN) [<0000000000240fac>] idle_loop+0x134/0x154 >> (XEN) [<000000000024c160>] start_secondary+0x14c/0x15c >> (XEN) [<0000000000000001>] 0000000000000001 >> >> The proper solution is to context switch the virtual interrupt state at >> the GIC level. This would also avoid masking the output signal which >> requires specific handling in the guest OS and more complex code in Xen >> to deal with EOIs, and so is desirable for that reason too. >> >> Sadly, this solution requires some refactoring which would not be >> suitable for a freeze exception for the Xen 4.5 release. >> >> For now implement a temporary solution which ignores the virtual timer >> interrupt when the idle VCPU is running. >> > > When we reschedule the vcpu which caused the spurious interrupt, the IRQ > will definitely trigger again for real, right? Xen arms a timer when the domain is saved. As we received an unexpected interrupt that means the timer expires which will make Xen injected the virtual timer interrupt (see virt_timer_expired). >> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx> > > Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx> > > I'll defer applying until you've said Yes to the above question. > >> diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c >> index a6436f1..471d7a9 100644 >> --- a/xen/arch/arm/time.c >> +++ b/xen/arch/arm/time.c >> @@ -169,6 +169,19 @@ static void timer_interrupt(int irq, void *dev_id, >> struct cpu_user_regs *regs) >> >> static void vtimer_interrupt(int irq, void *dev_id, struct cpu_user_regs >> *regs) >> { >> + /* >> + * Edge-triggered interrupt can be used for the virtual timer. Even > > "interrupts" > >> + * if the timer output signal is masked in the context switch, the >> + * GIC will keep track that of any interrupts raised while IRQS as > > s/as/are/ > > I'll fix those on commit. Thanks! Regards, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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