Re: [Qemu-devel] [PATCH v2] i386: Add new Hygon 'Dhyana' CPU model

[Daniel P . Berrangé]

On Tue, Apr 16, 2019 at 02:56:12PM +0800, Pu Wen wrote:
> On 2019/4/15 17:25, Daniel P. Berrangé wrote:
> > On Sat, Apr 13, 2019 at 10:54:40AM +0800, Pu Wen wrote:
> ...
> > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > index f2c15bf..551bec9 100644
> > > --- a/hw/i386/pc.c
> > > +++ b/hw/i386/pc.c
> > > @@ -128,6 +128,8 @@ GlobalProperty pc_compat_3_1[] = {
> > >       { "EPYC" "-" TYPE_X86_CPU, "nrip-save", "off" },
> > >       { "EPYC-IBPB" "-" TYPE_X86_CPU, "npt", "off" },
> > >       { "EPYC-IBPB" "-" TYPE_X86_CPU, "nrip-save", "off" },
> > > +    { "Dhyana" "-" TYPE_X86_CPU, "npt", "off" },
> > > +    { "Dhyana" "-" TYPE_X86_CPU, "nrip-save", "off" },
> > >       { "Skylake-Client" "-" TYPE_X86_CPU,      "mpx", "on" },
> > >       { "Skylake-Client-IBRS" "-" TYPE_X86_CPU, "mpx", "on" },
> > >       { "Skylake-Server" "-" TYPE_X86_CPU,      "mpx", "on" },
> > > @@ -152,6 +154,7 @@ GlobalProperty pc_compat_2_12[] = {
> > >       { TYPE_X86_CPU, "topoext", "off" },
> > >       { "EPYC-" TYPE_X86_CPU, "xlevel", "0x8000000a" },
> > >       { "EPYC-IBPB-" TYPE_X86_CPU, "xlevel", "0x8000000a" },
> > > +    { "Dhyana-" TYPE_X86_CPU, "xlevel", "0x8000000a" },
> > >   };
> > >   const size_t pc_compat_2_12_len = G_N_ELEMENTS(pc_compat_2_12);
> > 
> > You can drop the changes in this file. This CPU model didn't exist
> > in any older QEMU releases, so there's no machine type backcompat
> > required, at least from upstream QEMU POV.
> 
> Then how about running QEMU with the parameter like "-M pc-i440fx-2.12"?
> Although the default machine is newer than that.

That doesnt matter.  This back-compat property table is about ensuring
that "-cpu Skylake-Client -M pc-i440fx-2.12" run on QEMU 4.0.0 release
works the same way as when run on QEMU 2.12.0 release.

Since there is no Dhyana CPU model in QEMU 2.12.0 release, there's no
back compat issue to fix.

Regards,
Daniel
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