Re: [Xen-devel] xc_altp2m_set_vcpu_enable_notify fail

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, May 02, 2016 at 07:42:34PM +0800, Big Strong wrote:
> >
> > Check the errno please, thats' where the information is stored.
> 
> 
> I looked up in the source code of xen 4.6, and find that errno 4 indicates
> "Interrupted system call
> <http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/include/public/errno.h;h=8c88bb1d40ff370c2824bb214bddfda4540528ed;hb=b24ad7ba911a9f0688ab179736476e44c52144f1#l36>",
> I'm not sure if it is the cause.
> 

That error number is internal to Xen, so you could be looking at the
wrong source.

The errno business is a bit messy. In general privcmd translates Xen's
errno into OS's errno. So in this case you need to look at your
operating system's errno.

> Another information about VMFUNC error is from the Intel Manual:
> 
> 25.5.5.2 General Operation of the VMFUNC Instruction
> > The VMFUNC instruction causes an invalid-opcode exception (#UD) if the
> > “enable VM functions” VM-execution
> > controls is 0 or the value of EAX is greater than 63 (only VM functions
> > 0–63 can be enable). Otherwise, the
> > instruction causes a VM exit if the bit at position EAX is 0 in the
> > VM-function controls (the selected VM function is
> > not enabled). If such a VM exit occurs, the basic exit reason used is 59
> > (3BH), indicating “VMFUNC”, and the length
> > of the VMFUNC instruction is saved into the VM-exit instruction-length
> > field. If the instruction causes neither an
> > invalid-opcode exception nor a VM exit due to a disabled VM function, it
> > performs the functionality of the
> > VM function specified by the value in EAX.
> 
> 
>  i.e. In conditions when guest software invoked a VM function with the
> VMFUNC instruction and the VM function either was not
> enabled or generated a function-specific condition causing a VM exit.
> 
> But I've already enabled VM function and the conditions described in the
> manual are not true (EAX is 0), so I'm still not clear the real reason

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