Re: [kvm-devel] [RFC][PATCH 3/4] kvm-vmx: KVM_EXIT_DEBUG on #BP exceptions

[Avi Kivity <avi@qumranet.com>]

Jan Kiszka wrote:
> Avi Kivity wrote:
>   
>> Jan Kiszka wrote:
>>     
>>> In order to allow the gdbstub of QEMU to push (soft) breakpoint handling
>>> completely into the gdb frontend, this patch enables guest exits also
>>> for #BP exceptions - in case guest debugging was turned on.
>>>
>>> Along this enhancement, this patch also fixes the flag manipulation for
>>> the singlestep mode.
>>>   
>>>       
>> Suppose userspace determines the exception is due to a guest
>> breakpoint.  How does it inject the debug exception?
>>     
>
> Good question. Is there no "inject exception #XX" mechanism in kvm yet?
>
>   

No userspace interface for it.  The kernel injects plenty 
(kvm_queue_exception).

> Will need this, as my current impression is that we better keep track of
> breakpoints at qemu level to tell guest soft-BPs apart from host
> injected ones. Would you suggest to add a separate IOCTL for exception
> injection then? Or should the new guest debug IOCTL contain a flag that
> signals "inject breakpoint trap" (both for guest soft-BP hits as well as
> guests already in single step mode)?

A debug specific thing may allow us to limit the generality of the 
implementation.

Or maybe, disable int 3 trapping, single step, reenable int 3 trapping 
-> no need to inject vectors.

-- 
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