Re: [Xen-devel] [PATCH biosdevname]: handle dom0 on AMD systems

[Olaf Hering]

Hello,

and ping.

Olaf


On Wed, Aug 17, Olaf Hering wrote:

> Starting with xen-4.7 cpuid() will return with the hypervisor bit set
> in a dom0 when running on an AMD system. As a result biosdevname
> thinks it runs in a guest and does nothing. Detect a dom0 by looking
> into xenfs. This works with classic xenlinux based kernels and with
> pvops based kernels.
> 
> Signed-off-by: Olaf Hering 
> 
> ---
>  src/bios_dev_name.c |   31 +++
>  1 file changed, 31 insertions(+)
> 
> --- a/src/bios_dev_name.c
> +++ b/src/bios_dev_name.c
> @@ -133,6 +133,31 @@ cpuid (u_int32_t eax, u_int32_t ecx)
>  }
>  
>  /*
> +  Starting with xen-4.7 cpuid will return with the hypervisor bit set
> +  on AMD systems. This breaks biosdevname and network interface names.
> +  Instead of relying on cpuid check for dom0 in xenfs.
> +*/
> +static int
> +running_in_dom0(void)
> +{
> +size_t len = 0;
> +char buf[16];
> +FILE *f = fopen("/proc/xen/capabilities", "r");
> +
> +if (!f)
> +return 0;
> +memset(buf, 0, sizeof(buf));
> +len = fread(, 1, sizeof(buf) - 1, f);
> +fclose(f);
> +while(len && --len && len < sizeof(buf)) {
> +if (buf[len] == '\n')
> +buf[len] = '\0';
> +}
> +len = !strcmp("control_d", buf);
> +return len;
> +}
> +
> +/*
>Algorithm suggested by:
>
> http://kb.vmware.com/selfservice/microsites/search.do?language=en_US=displayKC=1009458
>  */
> @@ -144,7 +171,11 @@ running_in_virtual_machine (void)
>  
>  ecx = cpuid (eax, ecx);
>  if (ecx & 0x8000U)
> +{
> +   if (running_in_dom0())
> +   return 0;
> return 1;
> +}
>  return 0;
>  }
>  




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Re: [Xen-devel] [PATCH biosdevname]: handle dom0 on AMD systems

[Andrew Cooper]

On 17/08/16 12:51, Jan Beulich wrote:
 On 17.08.16 at 12:30,  wrote:
>> @@ -144,7 +171,11 @@ running_in_virtual_machine (void)
>>  
>>  ecx = cpuid (eax, ecx);
>>  if (ecx & 0x8000U)
>> +{
>> +   if (running_in_dom0())
>> +   return 0;
>> return 1;
>> +}
>>  return 0;
>>  }
> Isn't this backwards? Dom0 _is_ a virtual machine.

biosdevname uses it as a "I should silently exit and do nothing" check.

This is unhelpful behaviour as dom0 is responsible for the real hardware.

~Andrew

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Re: [Xen-devel] [PATCH biosdevname]: handle dom0 on AMD systems

[Jan Beulich]

>>> On 17.08.16 at 12:30,  wrote:
> @@ -144,7 +171,11 @@ running_in_virtual_machine (void)
>  
>  ecx = cpuid (eax, ecx);
>  if (ecx & 0x8000U)
> +{
> +   if (running_in_dom0())
> +   return 0;
> return 1;
> +}
>  return 0;
>  }

Isn't this backwards? Dom0 _is_ a virtual machine.

Jan


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