Re: [PATCH 0/4] hw/s390x: Alias @dump-skeys -> @dump-s390-skey and deprecate

[Thomas Huth]

On 31/05/2024 16.02, Dr. David Alan Gilbert wrote:
> * Thomas Huth (thuth@redhat.com) wrote:
> > On 30/05/2024 09.45, Philippe Mathieu-Daudé wrote:
> > > We are trying to unify all qemu-system-FOO to a single binary.
> > > In order to do that we need to remove QAPI target specific code.
> > >
> > > @dump-skeys is only available on qemu-system-s390x. This series
> > > rename it as @dump-s390-skey, making it available on other
> > > binaries. We take care of backward compatibility via deprecation.
> > >
> > > Philippe Mathieu-Daudé (4):
> > >     hw/s390x: Introduce the @dump-s390-skeys QMP command
> > >     hw/s390x: Introduce the 'dump_s390_skeys' HMP command
> > >     hw/s390x: Deprecate the HMP 'dump_skeys' command
> > >     hw/s390x: Deprecate the QMP @dump-skeys command
> >
> > Why do we have to rename the command? Just for the sake of it? I think
> > renaming HMP commands is maybe ok, but breaking the API in QMP is something
> > you should consider twice.
> >
> > And even if we decide to rename ... maybe we should discuss whether it makes
> > sense to come up with a generic command instead: As far as I know, ARM also
> > has something similar, called MTE. Maybe we also want to dump MTE keys one
> > day? So the new command should maybe be called "dump-memory-keys" instead?
>
> I think there are at least two different concepts; but I agree it would be
> nice to keep a single command for matching concepts across different 
> architectures;
> I can't say I know the details of any, but:
>
>    a) Page table things - I think x86 PKRU/PKEY (???) is a page table thing
>      where pages marked a special way are associated with keys.
>      That sounds similar to what the skeys are???

Sounds a little bit similar, but s390 storage keys are independent from page 
tables. It's rather that each page (4096 bytes) of RAM has an additional 
7-bit value that contains the storage key and some additional bits. It's 
also usable when page tables are still disabled.

> I'm not sure the two fit in the same command.

Does it make sense to dump all the MTE or x86 keys all at once? If so, we 
could maybe come up with an unified command. Otherwise it might not make 
sense, indeed.

 Thomas