Re: [Xen-devel] xc_altp2m_set_vcpu_enable_notify fail

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Thu, May 12, 2016 at 9:17 AM, Wei Liu <wei.liu2@xxxxxxxxxx> wrote:
> On Thu, May 12, 2016 at 09:00:12PM +0800, Big Strong wrote:
>> I'm still not very clear why would do_altp2m_op change the domain to
>> current domain (which is dom0 in my case) when the cmd is
>> HVMOP_altp2m_vcpu_enable_notify
>> <http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/hvm/hvm.c;hb=743289d0296268fe6bad64531a24d8053afeb062#l6198>.
>> As to my case, it would prevent the dom0 to set the #ve info page for other
>> domUs because the check of is_hvm_domain would fail
>> <http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/hvm/hvm.c;hb=743289d0296268fe6bad64531a24d8053afeb062#l6204>and
>> the function will returns directly.
>>
>
> Maybe the intent of that HVMOP is to get called directly by the guest
> that is interested in such event?
>
> I looks like a natural restriction to me because the vcpu needs to set
> up handler for #ve AIUI. It's not likely that Dom0 can do this for
> arbitrary guest.
>

That sounds like a reasonable explanation. When I wrote the libxc
wrapper I pretty much just exposed what was available based on the
hypervisor side. As my off-hand comment in the code states I did find
it odd that this op works on current vCPU. So if it's actually issued
from the domain itself it would make sense. So with that we should
probably remove the libxc wrapper for this hvmop as it won't work/not
designed to be issued from dom0 and should add some comments in the
header explaining its intended use.

Tamas

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