RE: [PATCH v2] i386: Add the support for AMD EPYC 3rd generation processors

[Babu Moger]

> -----Original Message-----
> From: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
> Sent: Monday, March 1, 2021 2:22 PM
> To: Moger, Babu <Babu.Moger@amd.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>; Paolo Bonzini
> <pbonzini@redhat.com>; richard.henderson@linaro.org; Eduardo Habkost
> <ehabkost@redhat.com>; Qemu Developers <qemu-devel@nongnu.org>
> Subject: Re: [PATCH v2] i386: Add the support for AMD EPYC 3rd generation
> processors
> 
> > > Hi Babu,
> > >
> > > I tried to test below patch for AMD EPYC Rome CPU and I got below error
> [1]:
> > >
> > > Also, I noticed SSBD CPU flag for guest was still available even
> > > without this patch, I noticed that for the guest, AMD_SSBD not got set.
> > >
> > > Guest:
> > > 0x80000008 0x00: eax=0x00003028 ebx=0x00009205 ecx=0x00002003
> > > edx=0x00000000
> > >
> > > [1]
> > > [    0.008000] unchecked MSR access error: WRMSR to 0x48 (tried to
> > > write 0x0000000000000000) at rIP: 0xffffffff9245c9e4
> > > (native_write_msr+0x4/0x20)
> > > [    0.008000]  [<ffffffff9243a6c5>] ? x86_spec_ctrl_setup_ap+0x35/0x50
> > > [    0.008000]  [<ffffffff92439423>] ? identify_secondary_cpu+0x53/0x80
> > > [    0.008000]  [<ffffffff9244adfa>] ? start_secondary+0x6a/0x1b0
> > >
> > > 0.011970] unchecked MSR access error: RDMSR from 0x48 at rIP:
> > > 0xffffffff9245c772 (native_read_msr+0x2/0x40)
> >
> > I did not see any problem with these patches.
> > My guest setup.
> > # lscpu |grep -o ssbd
> > ssbd
> > [root@rome-vm ~]# uname -r
> > 4.18.0-147.el8.x86_64
> > [root@rome-vm ~]# cat /etc/redhat-release Red Hat Enterprise Linux
> > release 8.1 (Ootpa) # wrmsr 0x48 7 [root@rome-vm ~]# rdmsr 0x48
> > 7
> >
> >
> > My host os.
> > # uname -r
> > 4.18.0-193.el8.x86_64
> > [root@rome images]# cat /etc/redhat-release Red Hat Enterprise Linux
> > release 8.2 Beta (Ootpa)
> >
> > Also, I only see ssbd feature when add this patch(EPYC-Rome-v2).
> > Otherwise, I don’t see ssbd feature.
> 
> Thanks for checking!
> Can you also see the ibrs feature inside guest with this patch?

Yes, The feature is available with this patch. Otherwise it is not available.
[root@rome-vm ~]# lscpu |grep -o ibrs
ibrs

> 
> Thanks,
> Pankaj
> >
> > Thanks
> > Babu
> >
> >
> > >
> > > Thanks,
> > > Pankaj
> > >
> > > > > It is normally added as v2 for compatibility. Like this.
> > > >
> > > > o.k. Thanks!
> > > > I will test this tomorrow.
> > > >
> > > > >
> > > > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c index
> > > > > 24db7ed892..f721d0db78 100644
> > > > > --- a/target/i386/cpu.c
> > > > > +++ b/target/i386/cpu.c
> > > > > @@ -4179,6 +4179,20 @@ static X86CPUDefinition builtin_x86_defs[] =
> {
> > > > >          .xlevel = 0x8000001E,
> > > > >          .model_id = "AMD EPYC-Rome Processor",
> > > > >          .cache_info = &epyc_rome_cache_info,
> > > > > +        .versions = (X86CPUVersionDefinition[]) {
> > > > > +            { .version = 1 },
> > > > > +            {
> > > > > +                .version = 2,
> > > > > +                .props = (PropValue[]) {
> > > > > +                    { "ibrs", "on" },
> > > > > +                    { "amd-ssbd", "on" },
> > > > > +                    { "model-id",
> > > > > +                      "AMD EPYC-Rome Processor" },
> > > > > +                    { /* end of list */ }
> > > > > +                }
> > > > > +            },
> > > > > +            { /* end of list */ }
> > > > > +        }
> > > > >      },
> > > > >      {
> > > > >          .name = "EPYC-Milan",