Re: [Xen-devel] SVM Trap Flag exiting?

[Tim Deegan <tim@xxxxxxx>]

At 11:37 -0400 on 25 Sep (1348573069), Cutter 409 wrote:
> I'm having a really hard time trying to accomplish something that seems
> generally simple. I want to single step some code in an SVM guest.
> 
> My current method essentially does the following:
> 
> From a domctl:
>    * Pause the target VCPU
>    * vmcb_set_exception_intercepts(vmcb,
> vmcb_get_exception_intercepts(vmcb) | (1U << TRAP_debug) );
>    * v->arch.guest_context.user_regs.rflags |= X86_EFLAGS_TF;
>    * I've also tried vmcb->rflags |= X86_EFLAGS_TF;
>    * Unpause the VCPU
> 
> But the VMEXIT_EXCEPTION_DB case doesn't ever seem to get called. Is there
> something I'm missing here?

Hard to tell without seeing your patch.  Did you see the code in
svm_do_resume that clears TRAP_debug from the intercept mask if it
doesn't think there's a debugger attached?

Have you considered using the existing debugger_attached mechanism
rather than adding your own?

Tim

> I've also tried setting both versions of rflags in svm_do_resume() but it
> doesn't make a difference.The guest doesn't crash either, so I'm assuming
> TF is just not getting set.
> 
> Any thoughts would be greatly appreciated.
> 
> Thanks!

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