Re: [PATCH v4 4/7] target/i386: Add feature bits for CPUID_Fn80000021_EAX

[Paolo Bonzini]

On 5/4/23 22:53, Babu Moger wrote:
> Add the following feature bits.
> no-nested-data-bp         : Processor ignores nested data breakpoints.

This bit is useless, unfortunately.  Another similar bit include the one 
about availability of FCS/FDS in the x87 save state.

They say that something is _not_ available, so a strict interpretation 
would prevent migrating from any old processor to Genoa, because in 
theory you never know if guests are using nested data breakpoints.

In practice, this does not really matter because no one used 
them---that's why AMD could get away with removing them---but please 
tell the architects that while they're free to deprecate and remove old 
features, adding CPUID is basically pointless.

Paolo