Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1653345

Re: [RFC] KVM: SVM: do not drop VMCB CPL to 0 if SS is not present

Show all headers | View raw

On 30/05/2017 17:58, Roman Penyaev wrote:
> Indeed, what is left is eventually take it from SS.RPL. J.

Ahah! :)  But I only suggested that in specific cases.

> But jokes aside,  with your last patch you seems fixed a race problem
> when "CS.RPL is not equal to the CPL in the few instructions between
> setting CR0.PE and reloading CS".

Yes, exactly.  The symptom was a crash (triple fault) when you kept
interrupting with "info cpus" a guest that repeatedly went to protected
mode and back to real mode.

> We will have CPL in var->dpl, and it seems ok.  All we need is not
> to lose it on the way kernel->userspace->kernel.

You're right.  So what do you think of the other suggestion (svm.c
doesn't clear attributes for unusable registers, QEMU only clears P for
unusable registers)?

Thanks,

Paolo

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [RFC] KVM: SVM: do not drop VMCB CPL to 0 if SS is not present Paolo Bonzini <pbonzini@redhat.com> - 2017-05-30 17:20 +0200
  Re: [RFC] KVM: SVM: do not drop VMCB CPL to 0 if SS is not present Roman Penyaev <roman.penyaev@profitbricks.com> - 2017-05-30 18:00 +0200
    Re: [RFC] KVM: SVM: do not drop VMCB CPL to 0 if SS is not present Paolo Bonzini <pbonzini@redhat.com> - 2017-05-30 18:10 +0200
      Re: [RFC] KVM: SVM: do not drop VMCB CPL to 0 if SS is not present Gi-Oh Kim <gi-oh.kim@profitbricks.com> - 2017-05-30 18:40 +0200

csiph-web