Re: [PATCH] x86: convert BUG_ON()s to WARN_ON()s in read_descriptor()

[Keir Fraser <keir.xen@gmail.com>]

On 16/12/2011 14:44, "Jan Beulich" <JBeulich@suse.com> wrote:

>>>> On 16.12.11 at 10:09, Keir Fraser <keir.xen@gmail.com> wrote:
>> On 15/12/2011 10:25, "Jan Beulich" <JBeulich@suse.com> wrote:
>> 
>>> In the light of AMD erratum #700, and given that these checks happen
>>> for debugging purposes only and also only in debug builds of the
>>> hypervisor, make the failures non-fatal.
>> 
>> I think the changeset comment should have a brief description of erratum
>> #700.
> 
> I'd do this, but ...
> 
>> I also some reference should be made in a comment above the first
>> WARN_ON, explaining why they are now WARN_Ons (again, with reference to #700
>> and its symptoms).
> 
> ... I now think that these should never have been BUG_ON()s in the
> first place (despite probably having been the one who introduced
> them).
> 
> Additionally, on a second look, check_descriptor() would not allow any
> of the affected selector types to be installed into a descriptor table,
> and we clearly don't put in any such descriptors ourselves, so from the
> perspective of the erratum we're okay without the patch.
> 
> So if you prefer them to stay BUG_ON(), I think I'll just withdraw the
> patch.

If the erratum cannot affect us then they may as well stay as BUG_ON and we
sidestep the whole thing.

 -- Keir

> Jan
> 
>> Apart from that:
>> Acked-by: Keir Fraser <keir@xen.org>
>> 
>>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>> 
>>> --- a/xen/arch/x86/traps.c
>>> +++ b/xen/arch/x86/traps.c
>>> @@ -1544,11 +1544,11 @@ static int read_descriptor(unsigned int
>>>              asm volatile (
>>>                  "larl %2,%0 ; setz %1"
>>>                  : "=r" (a), "=qm" (valid) : "rm" (sel));
>>> -            BUG_ON(valid && ((a & 0x00f0ff00) != *ar));
>>> +            WARN_ON(valid && ((a & 0x00f0ff00) != *ar));
>>>              asm volatile (
>>>                  "lsll %2,%0 ; setz %1"
>>>                  : "=r" (l), "=qm" (valid) : "rm" (sel));
>>> -            BUG_ON(valid && (l != *limit));
>>> +            WARN_ON(valid && (l != *limit));
>>>          }
>>>  #endif
>>>      }
>>> 
>>> 
>>> 
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> 
> 
>