Re: [Xen-devel] HVMOP_altp2m_vcpu_enable_notify code example usage

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

On Mon, Aug 22, 2016 at 12:42 PM, Dmitry Rockosov <rockosov@xxxxxxxxx> wrote:
> Tamas, what do you think, why the same hypercall operations (get_param) are
> executed by Xen differently? Does Xen know anything about caller domU CPL:
> usermode or kernelmode?

It's not about the guest's CPL - all hypercalls are issued ultimately
from kernelmode anyway - but depending on which HVMOP the guest issues
it can get treated differently by Xen. You can follow the path from
here: 
https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/x86/hvm/hvm.c;h=0180f26b56b75c08c8c53b58a599de6085949bce;hb=HEAD#l5510.
I'm not sure which HVMOPs are allowed by default to be executed by the
guest itself.

Tamas

>
> Thank you for answers!
>
> Best Regards,
> Rockosov Dmitry
>
> 2016-08-22 21:28 GMT+03:00 Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>:
>>
>> On Mon, Aug 22, 2016 at 12:12 PM, Dmitry Rockosov <rockosov@xxxxxxxxx>
>> wrote:
>> > The problem is in hypervisor checking definitely. I deeper debugged the
>> > code, I met vmcall instruction execution. This means EFAULT is coming
>> > from
>> > hypervisor.
>>
>> As it should, question is where exactly it gets denied in Xen.
>>
>> >
>> > Best Regards,
>> > Rockosov Dmitry
>> >
>> > 2016-08-22 18:09 GMT+03:00 Dmitry Rockosov <rockosov@xxxxxxxxx>:
>> >>
>> >> Hello Tamas,
>> >>
>> >> Thank you for the answer!
>> >>
>> >> I installed the same xen source code (4.7.0) as on dom0 to domU, built
>> >> dist-tools, installed xen-tools, updated rc.d configuration and
>> >> rebooted.
>> >> IOCTL channel to privcmd driver is working fine, but all requests to
>> >> hypervisor like hvm_get_param, translate_foreign_address,
>> >> altp2m_vcpu_enable_notify return EFAULT errno (Bad access).
>> >>
>> >> Just for experiment I wrote below code in usermode:
>> >> ===================================
>> >> ...
>> >> rc = xc_hvm_param_get(xch, DOMID_SELF, HVM_PARAM_CONSOLE_PFN, &value);
>> >> if (rc < 0) {
>> >>     PERROR("Fail to get CONSOLE PFN HVM PARAM\n");
>> >>     goto exit;
>> >> }
>> >> DPRINTF("CONSOLE PFN == %llx", (unsigned long long)value);
>> >> ...
>> >> ===================================
>> >>
>> >> and below code in kernelmode:
>> >> ===================================
>> >> ...
>> >> printk(KERN_INFO "We are in Xen domain HVM = %d\n", xen_hvm_domain());
>> >> err = hvm_get_parameter(HVM_PARAM_CONSOLE_PFN, &value);
>> >> printk(KERN_INFO "err = %d\n", err);
>> >> printk(KERN_INFO "CONSOLE PFN = %llx\n", value);
>> >> ...
>> >> ===================================
>> >>
>> >> In the usermode I got an error:
>> >> ===================================
>> >> Fail to get CONSOLE PFN HVM PARAM
>> >> : Bad address
>> >> ===================================
>> >>
>> >> In the kernelmode code executed fine:
>> >> ===================================
>> >> [23261.230188] We are in Xen domain HVM = 1
>> >> [23261.307840] err = 0
>> >> [23261.352587] CONSOLE PFN = fefff
>> >> ===================================
>> >>
>> >> Looks like usermode wrappers don't support many requests to hypervisor,
>> >> right?
>>
>> Not sure about HVMOP_get_param but AFAIK for
>> HVMOP_altp2m_vcpu_enable_notify to work you would have to create the
>> domain with altp2mhvm=1 enabled, then also issue the required commands
>> from dom0 to enable it (xc_altp2m_set_domain_state) and also perhaps
>> create a couple altp2m views.
>>
>> Tamas
>>
>> >>
>> >> Best Regards,
>> >> Rockosov Dmitry
>> >>
>> >> 2016-08-21 20:27 GMT+03:00 Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>:
>> >>>
>> >>> Hi Dmitry,
>> >>> as long as you are testing with a HVM Linux guest you should be able
>> >>> to just compile the Xen tools in the guest and then use libxc from
>> >>> within the guest to issue that hypercall via
>> >>> xc_altp2m_set_vcpu_enable_notify. You will need to load a couple Xen
>> >>> related kernel-modules for it to work (like xen-privcmd). Let us know
>> >>> if you got it working!
>> >>>
>> >>> Cheers,
>> >>> Tamas
>> >>>
>> >>> On Fri, Aug 19, 2016 at 1:19 PM, Dmitry Rockosov <rockosov@xxxxxxxxx>
>> >>> wrote:
>> >>> > Hello Xen Team!
>> >>> >
>> >>> > Does anybody have any code examples of
>> >>> > HVMOP_altp2m_vcpu_enable_notify?
>> >>> >
>> >>> > I want to fully test #VE, VMFUNC and EPTP Switching VM Function 0 in
>> >>> > Xen,
>> >>> > but doesn't have any documentations/examples for it.
>> >>> > I tried xen-access test from tools/tests/xen-access, but looks like
>> >>> > it
>> >>> > doesn't use VMFUNC and #VE, it simply changes VMCS entries with
>> >>> > vmwrite, w/o
>> >>> > VMFUNC 0 (EPTP Switching).
>> >>> >
>> >>> > Thanks in advance!
>> >>> >
>> >>> > Best Regards,
>> >>> > Rockosov Dmitry
>> >>> >
>> >>> > _______________________________________________
>> >>> > Xen-devel mailing list
>> >>> > Xen-devel@xxxxxxxxxxxxx
>> >>> > https://lists.xen.org/xen-devel
>> >>> >
>> >>
>> >>
>> >
>
>

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