Messages in this thread | | | Subject | Possible nohz-full/RCU issue in arm64 KVM | From | Nicolas Saenz Julienne <> | Date | Fri, 17 Dec 2021 12:51:57 +0100 |
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Hi All, arm64's guest entry code does the following:
int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) { [...]
guest_enter_irqoff();
ret = kvm_call_hyp_ret(__kvm_vcpu_run, vcpu);
[...]
local_irq_enable();
/* * We do local_irq_enable() before calling guest_exit() so * that if a timer interrupt hits while running the guest we * account that tick as being spent in the guest. We enable * preemption after calling guest_exit() so that if we get * preempted we make sure ticks after that is not counted as * guest time. */ guest_exit(); [...] }
On a nohz-full CPU, guest_{enter,exit}() delimit an RCU extended quiescent state (EQS). Any interrupt happening between local_irq_enable() and guest_exit() should disable that EQS. Now, AFAICT all el0 interrupt handlers do the right thing if trggered in this context, but el1's won't. Is it possible to hit an el1 handler (for example __el1_irq()) there?
Thanks,
-- Nicolás Sáenz
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