Marcelo Tosatti wrote: > On Wed, Nov 11, 2009 at 09:07:08PM +0100, Jan Kiszka wrote: >> Marcelo Tosatti wrote: >>> From: Joerg Roedel <joerg.roedel@xxxxxxx> >>> >>> The current KVM x86 exception code handles double and triple faults only for >>> page fault exceptions. This patch extends this detection for every exception >>> that gets queued for the guest. >>> >>> Signed-off-by: Joerg Roedel <joerg.roedel@xxxxxxx> >>> CC: Jan Kiszka <jan.kiszka@xxxxxx> >> For a moment I felt like I was time traveling - back in '08. :) >> >> Reading the archive I noticed that someone posted a fix-up for this patch: >> >> http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/16931 >> >> Why don't we need this anymore? > > I suppose qemu-kvm's call to set_sregs (via system_reset) will end up > clearing pending exception? Right, forgot for the moment that triple fault implies user space. > >> Moreover, are we sure to not regress /wrt to the cases that shall be >> handled serially? So far they should have triggered the WARN_ON, right? > > Right. > > How can it regress though, given that serially handled exceptions are > not supported at the moment (you get a WARN_ON and lose the previously > queued anyway). The guest so far sees the second exception as the result, now it sees DF. So the behavior changes from broken to broken, but I wondered if the current state is already so broken that this change doesn't matter. Another micro difference is this: > @@ -184,24 +196,6 @@ void kvm_inject_page_fault(struct kvm_vc > { > ++vcpu->stat.pf_guest; > > - if (vcpu->arch.exception.pending) { > - switch(vcpu->arch.exception.nr) { > - case DF_VECTOR: > - /* triple fault -> shutdown */ > - set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests); > - return; > - case PF_VECTOR: > - vcpu->arch.exception.nr = DF_VECTOR; > - vcpu->arch.exception.error_code = 0; > - return; > - default: > - /* replace previous exception with a new one in a hope > - that instruction re-execution will regenerate lost > - exception */ > - vcpu->arch.exception.pending = false; > - break; > - } > - } > vcpu->arch.cr2 = addr; > kvm_queue_exception_e(vcpu, PF_VECTOR, error_code); > } So far cr2 was not touched on DF, now it is. Jan
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