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Re: [Xen-devel] [PATCH 3/9] x86/cpuid: Extend the cpuid= command line option to support all named features

>>> On 03.12.18 at 17:18, <andrew.cooper3@xxxxxxxxxx> 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(), introduce a slightly fuzzy strcmp() to accept changes in
> punctuation, and perform a binary search over INIT_FEATURE_NAMES.
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Slightly RFC, because I'm not entirely certain if this is a good idea or 
> not.

It is a good idea, but precautions are needed against attempts
to disable features we rely on (specifically ones inferred from us
running in 64-bit mode), or guests would equally rely on. I'm
therefore unsure whether the mere "named" fact for a feature
is a suitable criteria to allow its disabling from the command line.
Perhaps a second form of annotation in the public header is
needed? Or some minimal feature set to enforce?


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