no definition of virtualization exception in exception table

no definition of virtualization exception in exception table

[Big Strong]

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There is a #VE exception defined in p2086 of Intel Software Development
Manual, however, no definition of exception handler is availble in Xen 4.6.
<http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/x86_64/entry.S;h=d0f3259efe8b63a152fb413696b66cfb6a382345;hb=9772c480a71ad38cc2c342e4c2e78c2475de7268#l658>Should
I define the handler by myself by modifying the source code of xen, or is
there a way to define the handler of the reserved IDT vectors (0-31, #VE is
20) without modifying the source code?

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Re: no definition of virtualization exception in exception table

[George Dunlap]

On Thu, Apr 28, 2016 at 3:37 AM, Big Strong <fangtuo90@gmail.com> wrote:
> There is a #VE exception defined in p2086 of Intel Software Development
> Manual, however, no definition of exception handler is availble in Xen 4.6.
> Should I define the handler by myself by modifying the source code of xen,
> or is there a way to define the handler of the reserved IDT vectors (0-31,
> #VE is 20) without modifying the source code?

What are you actually trying to do?

Xen shouldn't be generating #VEs itself, so it doesn't need a #VE
handler.  Those should only be generated by guests in HVM mode (if I'm
remembering things correctly).  In those cases the #VE will either be
delivered directly to the guest, or it will cause a VMEXIT.

 -George

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Re: no definition of virtualization exception in exception table

[Andrew Cooper]

On 28/04/16 09:53, George Dunlap wrote:
> On Thu, Apr 28, 2016 at 3:37 AM, Big Strong <fangtuo90@gmail.com> wrote:
>> There is a #VE exception defined in p2086 of Intel Software Development
>> Manual, however, no definition of exception handler is availble in Xen 4.6.
>> Should I define the handler by myself by modifying the source code of xen,
>> or is there a way to define the handler of the reserved IDT vectors (0-31,
>> #VE is 20) without modifying the source code?
> What are you actually trying to do?
>
> Xen shouldn't be generating #VEs itself, so it doesn't need a #VE
> handler.  Those should only be generated by guests in HVM mode (if I'm
> remembering things correctly).  In those cases the #VE will either be
> delivered directly to the guest, or it will cause a VMEXIT.

Correct.  #VE occurs from a EPT permission violation when appropriate
controls are set up, and are either become a VMEXIT or an in-guest #VE
depending on the .surpress_ve bit in a leaf epte.

Unless you are nesting Xen inside another hypervisor on Intel hardware,
and have opted in to receiving #VE's, you won't encounter any.

~Andrew

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Re: no definition of virtualization exception in exception table

[Big Strong]

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Got it. Thanks for the replying.

2016-04-28 17:03 GMT+08:00 Andrew Cooper <andrew.cooper3@citrix.com>:

> On 28/04/16 09:53, George Dunlap wrote:
> > On Thu, Apr 28, 2016 at 3:37 AM, Big Strong <fangtuo90@gmail.com> wrote:
> >> There is a #VE exception defined in p2086 of Intel Software Development
> >> Manual, however, no definition of exception handler is availble in Xen
> 4.6.
> >> Should I define the handler by myself by modifying the source code of
> xen,
> >> or is there a way to define the handler of the reserved IDT vectors
> (0-31,
> >> #VE is 20) without modifying the source code?
> > What are you actually trying to do?
> >
> > Xen shouldn't be generating #VEs itself, so it doesn't need a #VE
> > handler.  Those should only be generated by guests in HVM mode (if I'm
> > remembering things correctly).  In those cases the #VE will either be
> > delivered directly to the guest, or it will cause a VMEXIT.
>
> Correct.  #VE occurs from a EPT permission violation when appropriate
> controls are set up, and are either become a VMEXIT or an in-guest #VE
> depending on the .surpress_ve bit in a leaf epte.
>
> Unless you are nesting Xen inside another hypervisor on Intel hardware,
> and have opted in to receiving #VE's, you won't encounter any.
>
> ~Andrew
>

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