Messages in this thread | | | Date | Mon, 23 Aug 2021 22:51:48 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH] KVM: arm64: Ratelimit error log during guest debug exception |
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On 2021-08-23 19:13, Raghavendra Rao Ananta wrote: > On Sat, Aug 21, 2021 at 3:56 AM Marc Zyngier <maz@kernel.org> wrote: >> >> On Sat, 21 Aug 2021 00:01:24 +0100, >> Raghavendra Rao Ananta <rananta@google.com> wrote: >> > >> > [1 <text/plain; UTF-8 (7bit)>] >> > On Fri, Aug 20, 2021 at 2:29 AM Marc Zyngier <maz@kernel.org> wrote: >> > > >> > > On Thu, 19 Aug 2021 23:34:06 +0100, >> > > Raghavendra Rao Ananta <rananta@google.com> wrote: >> > > > >> > > > Potentially, the guests could trigger a debug exception that's >> > > > outside the exception class range. >> > > >> > > How? All the exception classes that lead to this functions are already >> > > handled in the switch/case statement. >> > > >> > I guess I didn't think this through. Landing into kvm_handle_guest_debug() >> > itself is not possible :) >> >> Exactly. >> >> > > My take on this is that this code isn't reachable, and that it could >> > > be better rewritten as: >> > > >> > > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c >> > > index 6f48336b1d86..ae7ec086827b 100644 >> > > --- a/arch/arm64/kvm/handle_exit.c >> > > +++ b/arch/arm64/kvm/handle_exit.c >> > > @@ -119,28 +119,14 @@ static int kvm_handle_guest_debug(struct kvm_vcpu >> > *vcpu) >> > > { >> > > struct kvm_run *run = vcpu->run; >> > > u32 esr = kvm_vcpu_get_esr(vcpu); >> > > - int ret = 0; >> > > >> > > run->exit_reason = KVM_EXIT_DEBUG; >> > > run->debug.arch.hsr = esr; >> > > >> > > - switch (ESR_ELx_EC(esr)) { >> > > - case ESR_ELx_EC_WATCHPT_LOW: >> > > + if (ESR_ELx_EC(esr) == ESR_ELx_EC_WATCHPT_LOW) >> > > run->debug.arch.far = vcpu->arch.fault.far_el2; >> > > - fallthrough; >> > > - case ESR_ELx_EC_SOFTSTP_LOW: >> > > - case ESR_ELx_EC_BREAKPT_LOW: >> > > - case ESR_ELx_EC_BKPT32: >> > > - case ESR_ELx_EC_BRK64: >> > > - break; >> > > - default: >> > > - kvm_err("%s: un-handled case esr: %#08x\n", >> > > - __func__, (unsigned int) esr); >> > > - ret = -1; >> > > - break; >> > > - } >> > > >> > > - return ret; >> > > + return 0; >> > > } >> > > >> > This looks better, but do you think we would be compromising on readability? >> >> I don't think so. The exit handler table is, on its own, pretty >> explicit about what we route to this handler, and the comment above >> the function clearly states that we exit to userspace for all the >> debug ECs. > > Sounds great. I'm happy to send out a patch with you as 'Suggested-by' > , if you > are okay with it.
Fire away!
M. -- Jazz is not dead. It just smells funny...
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