Re: [PATCH v2 4/6] docs/about/deprecated: Deprecate the qemu-system-arm binary

[Daniel P. Berrangé <berrange@xxxxxxxxxx>]

On Fri, Mar 03, 2023 at 12:31:42PM +0100, Thomas Huth wrote:
> On 03/03/2023 12.16, Peter Maydell wrote:
> > On Thu, 2 Mar 2023 at 16:31, Thomas Huth <thuth@xxxxxxxxxx> wrote:
> > > 
> > > qemu-system-aarch64 is a proper superset of qemu-system-arm,
> > > and the latter was mainly still required for 32-bit KVM support.
> > > But this 32-bit KVM arm support has been dropped in the Linux
> > > kernel a couple of years ago already, so we don't really need
> > > qemu-system-arm anymore, thus deprecated it now.
> > > 
> > > Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
> > > ---
> > >   docs/about/deprecated.rst | 10 ++++++++++
> > >   1 file changed, 10 insertions(+)
> > > 
> > > diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
> > > index a30aa8dfdf..21ce70b5c9 100644
> > > --- a/docs/about/deprecated.rst
> > > +++ b/docs/about/deprecated.rst
> > > @@ -45,6 +45,16 @@ run 32-bit guests by selecting a 32-bit CPU model, 
> > > including KVM support
> > >   on x86_64 hosts. Thus users are recommended to reconfigure their systems
> > >   to use the ``qemu-system-x86_64`` binary instead.
> > > 
> > > +``qemu-system-arm`` binary (since 8.0)
> > > +''''''''''''''''''''''''''''''''''''''
> > > +
> > > +``qemu-system-aarch64`` is a proper superset of ``qemu-system-arm``.
> > 
> > I think this is not quite true -- at the moment if you want
> > "every feature we implement, 32-bit" the only way to get
> > that is 'qemu-system-arm -cpu max'. The '-cpu max' on
> > qemu-system-aarch64 is 64-bit, and we don't implement for TCG
> > the "-cpu max,aarch64=off" syntax that we do for KVM that would
> > let the user say "no 64-bit support".
> 
> Ok ... so what does that mean now? ... can we continue with this patch, e.g.
> after rephrasing the text a little bit, or do we need to implement "-cpu
> max,aarch64=off" for TCG first?

I think we need to have a way to request the max 32-bit CPU before we
deprecate, because deprecation has to tell people what they should use
instead.

For qemu-system-i686 -cpu max, I guess we have lm=off to hide the 64-bit
support, so that's OK from QEMU POV, but will need libvirt enhancement
as I don't think we've taken that into account.


With regards,
Daniel
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