[PATCH 2/2] i386: Simplify CPUID_8000_001E for AMD

From: Babu Moger <babu.moger@amd.com>
To: pbonzini@redhat.com, rth@twiddle.net, ehabkost@redhat.com,
	mst@redhat.com,  marcel.apfelbaum@gmail.com
Cc: qemu-devel@nongnu.org
Subject: [PATCH 2/2] i386: Simplify CPUID_8000_001E for AMD
Date: Mon, 08 Jun 2020 15:18:56 -0500	[thread overview]
Message-ID: <159164753686.20543.4158548114186964547.stgit@naples-babu.amd.com> (raw)
In-Reply-To: <159164739269.20543.3074052993891532749.stgit@naples-babu.amd.com>

apic_id contains all the information required to build
CPUID_8000_001E. core_id and node_id is already part of
apic_id generated by x86_topo_ids_from_apicid_epyc.
Also remove the restriction on number bits on core_id and
node_id.

Remove all the hardcoded values and replace with generalized
fields.

Refer the Processor Programming Reference (PPR) documentation
available from the bugzilla Link below.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
Signed-off-by: Babu Moger <babu.moger@amd.com>
---
 target/i386/cpu.c |   78 +++++++++++++++++++++++++----------------------------
 1 file changed, 37 insertions(+), 41 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 3733d9a279..166d2f2bde 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -388,57 +388,53 @@ static void encode_topo_cpuid8000001e(X86CPUTopoInfo *topo_info, X86CPU *cpu,
 {
     X86CPUTopoIDs topo_ids = {0};
     unsigned long nodes = MAX(topo_info->nodes_per_pkg, 1);
-    int shift;
 
     x86_topo_ids_from_apicid_epyc(cpu->apic_id, topo_info, &topo_ids);
 
     *eax = cpu->apic_id;
+
     /*
+     * CPUID_Fn8000001E_EBX [Core Identifiers] (CoreId)
+     * Read-only. Reset: 0000_XXXXh.
+     * See Core::X86::Cpuid::ExtApicId.
+     * Core::X86::Cpuid::CoreId_lthree[1:0]_core[3:0]_thread[1:0];
      * CPUID_Fn8000001E_EBX
-     * 31:16 Reserved
-     * 15:8  Threads per core (The number of threads per core is
-     *       Threads per core + 1)
-     *  7:0  Core id (see bit decoding below)
-     *       SMT:
-     *           4:3 node id
-     *             2 Core complex id
-     *           1:0 Core id
-     *       Non SMT:
-     *           5:4 node id
-     *             3 Core complex id
-     *           1:0 Core id
+     * Bits Description
+     * 31:16 Reserved.
+     * 15:8 ThreadsPerCore: threads per core. Read-only. Reset: XXh.
+     *      The number of threads per core is ThreadsPerCore+1.
+     *  7:0 CoreId: core ID. Read-only. Reset: XXh.
+     *
+     *  NOTE: CoreId is already part of apic_id. Just use it. We can
+     *  use all the 8 bits to represent the core_id here.
      */
-    *ebx = ((topo_info->threads_per_core - 1) << 8) | (topo_ids.node_id << 3) |
-            (topo_ids.core_id);
+    *ebx = ((topo_info->threads_per_core - 1) << 8) | (topo_ids.core_id & 0xFF);
+
     /*
+     * CPUID_Fn8000001E_ECX [Node Identifiers] (NodeId)
+     * Read-only. Reset: 0000_0XXXh.
+     * Core::X86::Cpuid::NodeId_lthree[1:0]_core[3:0]_thread[1:0];
      * CPUID_Fn8000001E_ECX
-     * 31:11 Reserved
-     * 10:8  Nodes per processor (Nodes per processor is number of nodes + 1)
-     *  7:0  Node id (see bit decoding below)
-     *         2  Socket id
-     *       1:0  Node id
+     * Bits Description
+     * 31:11 Reserved.
+     * 10:8 NodesPerProcessor: Node per processor. Read-only. Reset: XXXb.
+     *      ValidValues:
+     *      Value Description
+     *      000b  1 node per processor.
+     *      001b  2 nodes per processor.
+     *      010b Reserved.
+     *      011b 4 nodes per processor.
+     *      111b-100b Reserved.
+     *  7:0 NodeId: Node ID. Read-only. Reset: XXh.
+     *
+     * NOTE: Hardware reserves 3 bits for number of nodes per processor.
+     * But users can create more nodes than the actual hardware can
+     * support. To genaralize we can use all the upper 8 bits for nodes.
+     * NodeId is combination of node and socket_id which is already decoded
+     * in apic_id. Just use it by shifting.
      */
-    if (nodes <= 4) {
-        *ecx = ((nodes - 1) << 8) | (topo_ids.pkg_id << 2) | topo_ids.node_id;
-    } else {
-        /*
-         * Node id fix up. Actual hardware supports up to 4 nodes. But with
-         * more than 32 cores, we may end up with more than 4 nodes.
-         * Node id is a combination of socket id and node id. Only requirement
-         * here is that this number should be unique accross the system.
-         * Shift the socket id to accommodate more nodes. We dont expect both
-         * socket id and node id to be big number at the same time. This is not
-         * an ideal config but we need to to support it. Max nodes we can have
-         * is 32 (255/8) with 8 cores per node and 255 max cores. We only need
-         * 5 bits for nodes. Find the left most set bit to represent the total
-         * number of nodes. find_last_bit returns last set bit(0 based). Left
-         * shift(+1) the socket id to represent all the nodes.
-         */
-        nodes -= 1;
-        shift = find_last_bit(&nodes, 8);
-        *ecx = (nodes << 8) | (topo_ids.pkg_id << (shift + 1)) |
-               topo_ids.node_id;
-    }
+    *ecx = ((nodes - 1) << 8) |
+            ((cpu->apic_id >> apicid_node_offset_epyc(topo_info)) & 0xFF);
     *edx = 0;
 }
 


