Re: [Xen-devel] [PATCH v2] x86/cpuid: Extend the cpuid= option to support all named features

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.09.2019 14:32, Andrew Cooper wrote:
> On 25/09/2019 13:30, Jan Beulich wrote:
>> On 05.09.2019 21:49, Andrew Cooper wrote:
>>> For gen-cpuid.py, fix a comment describing self.names, and generate the
>>> reverse mapping in self.values.  Write out INIT_FEATURE_NAMES which maps a
>>> string name to a bit position.
>>>
>>> For parse_cpuid(), use cmdline_strcmp() and perform a binary search over
>>> INIT_FEATURE_NAMES.  A tweak to cmdline_strcmp() is needed to break at 
>>> equals
>>> signs as well.
>>>
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> ---
>>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>>> CC: Wei Liu <wl@xxxxxxx>
>>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>>>
>>> v2:
>>>  * Rebase over cmdline_strcmp()
>>> ---
>>>  xen/arch/x86/cpuid.c   | 75 
>>> +++++++++++++++++++++++++++++++-------------------
>>>  xen/common/kernel.c    |  6 ++--
>>>  xen/include/xen/lib.h  |  4 +--
>>>  xen/tools/gen-cpuid.py | 22 +++++++++++++--
>>>  4 files changed, 71 insertions(+), 36 deletions(-)
>> I've noticed this only now: This change would have wanted to be
>> accompanied by an adjustment to the command line doc.
> 
> I debated that, but I don't want to give people the idea that using
> cpuid=no-lm might be a sensible thing to do.

Well, this is a particularly bad example. There are surely more
sensible forms of this option now which weren't previously
supported, and which aren't mentioned by the existing doc text.
The example you give suggests that we also want to have a
"minimal" policy, disabling of elements of which we should
reject when given to "cpuid=".

Jan

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