Re: [PATCH v11 3/5] i386: Add support for CPUID_8000_001E for AMD

Moger, Babu
2018-06-05T17:14:36Z

> -----Original Message-----
> From: kvm-owner@vger.kernel.org [mailto:kvm-owner@vger.kernel.org]
> On Behalf Of Moger, Babu
> Sent: Tuesday, June 5, 2018 10:49 AM
> To: Eduardo Habkost <ehabkost@redhat.com>
> Cc: mst@redhat.com; marcel.apfelbaum@gmail.com; pbonzini@redhat.com;
> rth@twiddle.net; mtosatti@redhat.com; geoff@hostfission.com;
> kash@tripleback.net; qemu-devel@nongnu.org; kvm@vger.kernel.org
> Subject: RE: [Qemu-devel] [PATCH v11 3/5] i386: Add support for
> CPUID_8000_001E for AMD
>
>
>
> > -----Original Message-----
> > From: Eduardo Habkost [mailto:ehabkost@redhat.com]
> > Sent: Monday, June 4, 2018 9:46 PM
> > To: Moger, Babu <Babu.Moger@amd.com>
> > Cc: mst@redhat.com; marcel.apfelbaum@gmail.com;
> pbonzini@redhat.com;
> > rth@twiddle.net; mtosatti@redhat.com; geoff@hostfission.com;
> > kash@tripleback.net; qemu-devel@nongnu.org; kvm@vger.kernel.org
> > Subject: Re: [Qemu-devel] [PATCH v11 3/5] i386: Add support for
> > CPUID_8000_001E for AMD
> >
> > On Thu, May 24, 2018 at 11:43:32AM -0400, Babu Moger wrote:
> > > Add support for cpuid leaf CPUID_8000_001E. Build the config that closely
> > > match the underlying hardware. Please refer to the Processor
> > Programming
> > > Reference (PPR) for AMD Family 17h Model for more details.
> > >
> > > Signed-off-by: Babu Moger <babu.moger@amd.com>
> > > ---
> > > target/i386/cpu.c | 61
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > > 1 file changed, 61 insertions(+)
> > >
> > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > > index 0d423e5..9f8bad9 100644
> > > --- a/target/i386/cpu.c
> > > +++ b/target/i386/cpu.c
> > > @@ -429,6 +429,62 @@ static void
> > encode_cache_cpuid8000001d(CPUCacheInfo *cache, CPUState *cs,
> > > (cache->complex_indexing ? CACHE_COMPLEX_IDX : 0);
> > > }
> > >
> > > +/* Data structure to hold the configuration info for a given core index */
> > > +struct core_topology {
> > > + /* core complex id of the current core index */
> > > + int ccx_id;
> > > + /* Adjusted core id for this core index in the topology */
> >
> > What's an "adjusted core id"?
>
> When you build the topology, "adjusted core id" is the core index inside the
> core complex.
> There can be max 4 cores in a core complex, so this id can be 0, 1, 2, 3. I will
> change the name to ccx_core_index;
> >
> > > + int core_id;
> > > + /* Node id for this core index */
> > > + int node_id;
> > > + /* Number of nodes in this config, 0 based */
> > > + int num_nodes;
> >
> > I suggest making num_nodes carry the actual number of nodes, and
> > using (num_nodes - 1) when building CPUID data.
>
> Sure. Will do
> >
> > > +};
> > > +
> > > +/*
> > > + * Build the configuration closely match the EPYC hardware. Using the
> > EPYC
> > > + * hardware configuration values (MAX_CCX, MAX_CORES_IN_CCX,
> > MAX_CORES_IN_NODE)
> > > + * right now. This could change in future.
> > > + * nr_cores : Total number of cores in the config
> > > + * core_id : Core index of the current CPU
> > > + * topo : Data structure to hold all the config info for this core index
> > > + */
> > > +static void build_core_topology(int nr_cores, int core_id,
> > > + struct core_topology *topo)
> > > +{
> > > + int nodes, cores_in_ccx;
> > > +
> > > + /* First get the number of nodes required */
> > > + nodes = nodes_in_socket(nr_cores);
> > > +
> > > + cores_in_ccx = cores_in_core_complex(nr_cores);
> > > +
> > > + topo->node_id = core_id / (cores_in_ccx * MAX_CCX);
> > > + topo->ccx_id = (core_id % (cores_in_ccx * MAX_CCX)) / cores_in_ccx;
> > > + topo->core_id = core_id % cores_in_ccx;
> > > + /* num_nodes is 0 based, return n - 1 */
> > > + topo->num_nodes = nodes - 1;
> > > +}
> >
> > Is this guaranteed to work with any nr_cores value, or only with
> > a few specific values that match real hardware?
>
> I have tested all the supported core values(1 to 32). All of them work fine.
>
> >
> >
> >
> > > +
> > > +/* Encode cache info for CPUID[8000001E] */
> > > +static void encode_topo_cpuid8000001e(CPUState *cs, X86CPU *cpu,
> > > + uint32_t *eax, uint32_t *ebx,
> > > + uint32_t *ecx, uint32_t *edx)
> > > +{
> > > + struct core_topology topo = {0};
> > > +
> > > + build_core_topology(cs->nr_cores, cpu->core_id, &topo);
> > > + *eax = cpu->apic_id;
> > > + if (cs->nr_threads - 1) {
> > > + *ebx = ((cs->nr_threads - 1) << 8) | (topo.node_id << 3) |
> > > + (topo.ccx_id << 2) | topo.core_id;
> > > + } else {
> > > + *ebx = (topo.node_id << 4) | (topo.ccx_id << 3) | topo.core_id;
> > > + }
> >
> > This part confuses me a lot. Where are those bit offsets in EBX
> > defined?
>
> Bit 7-0 is core id. This decodes to where in the topology the core is located.
> (2 bits for node, 2 bits for core complex and 3 bit index).

Sorry.. This should be 2 bits for node, 1 bit for core complex and 2 bits for index.
Will add comments..

> I will add those details in the comments.
>
> >
> > Is this guaranteed to work with any cs->nr_cores value?
> >
> >
> > > + *ecx = (topo.num_nodes << 8) | (cpu->socket_id << 2) |
> topo.node_id;
> >
> > Like on EBX, I'm confused by the bit offsets. Where are they
> > defined?
> >
>
> Bit 7-0 is Node id. This decodes to 1 bit for socket and 2 bits for node_id.
> I will add those details in comments.
>
> > Probably it's safer to not allow TOPOEXT to be enabled if the CPU
> > socket/core/thread topology configuration can't generate a sane
> > node/core-complex topology.
>
> Like I said before It may become too restrictive. I have tested all the
> numbers (1 to 32).
> They all appear to work ok.
>
> >
> >
> > > + *edx = 0;
> > > +}
> > > +
> > > /*
> > > * Definitions of the hardcoded cache entries we expose:
> > > * These are legacy cache values. If there is a need to change any
> > > @@ -4122,6 +4178,11 @@ void cpu_x86_cpuid(CPUX86State *env,
> > uint32_t index, uint32_t count,
> > > break;
> > > }
> > > break;
> > > + case 0x8000001E:
> > > + assert(cpu->core_id <= 255);
> > > + encode_topo_cpuid8000001e(cs, cpu,
> > > + eax, ebx, ecx, edx);
> > > + break;
> > > case 0xC0000000:
> > > *eax = env->cpuid_xlevel2;
> > > *ebx = 0;
> > > --
> > > 1.8.3.1
> > >
> > >
> >
> > --
> > Eduardo