[PATCH v2] i386/cpu: fixup number of addressable IDs for logical processors in the physical package

[Chuang Xu]

When QEMU is started with:
-cpu host,migratable=on,host-cache-info=on,l3-cache=off
-smp 180,sockets=2,dies=1,cores=45,threads=2

Execute "cpuid -1 -l 1 -r" in guest, we'll get:
eax=0x000806f8 ebx=0x465a0800 ecx=0xfffaba1f edx=0x3fa9fbff
CPUID.01H.EBX[23:16] is 90, while the expected value is 128.

Execute "cpuid -1 -l 4 -r" in guest, we'll get:
eax=0xfc004121 ebx=0x02c0003f ecx=0x0000003f edx=0x00000000
CPUID.04H.EAX[31:26] is 63, which is as expected.

As (1+CPUID.04H.EAX[31:26]) round up to the nearest power-of-2 integer,
we'd beter round up CPUID.01H.EBX[23:16] to the nearest power-of-2
integer too. Otherwise we may encounter unexpected results in guest.

For example, when QEMU is started with CLI above and xtopology is disabled,
guest kernel 5.15.120 uses CPUID.01H.EBX[23:16]/(1+CPUID.04H.EAX[31:26]) to
calculate threads-per-core in detect_ht(). Then guest will get "90/(1+63)=1"
as the result, even though theads-per-core should actually be 2.

So let us round up CPUID.01H.EBX[23:16] to the nearest power-of-2 integer
to solve the unexpected result.

Signed-off-by: Guixiong Wei <weiguixiong@bytedance.com>
Signed-off-by: Yipeng Yin <yinyipeng@bytedance.com>
Signed-off-by: Chuang Xu <xuchuangxclwt@bytedance.com>
---
 target/i386/cpu.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 4c2e6f3a71..24d60ead9e 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -261,6 +261,12 @@ static uint32_t max_thread_ids_for_cache(X86CPUTopoInfo 
*topo_info,
     return num_ids - 1;
 }
 
+static uint32_t max_thread_number_in_package(X86CPUTopoInfo *topo_info)
+{
+    uint32_t num_threads = 1 << apicid_pkg_offset(topo_info);
+    return num_threads;
+}
+
 static uint32_t max_core_ids_in_package(X86CPUTopoInfo *topo_info)
 {
     uint32_t num_cores = 1 << (apicid_pkg_offset(topo_info) -
@@ -6417,7 +6423,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
uint32_t count,
         }
         *edx = env->features[FEAT_1_EDX];
         if (threads_per_pkg > 1) {
-            *ebx |= threads_per_pkg << 16;
+            *ebx |= max_thread_number_in_package(&topo_info) << 16;
             *edx |= CPUID_HT;
         }
         if (!cpu->enable_pmu) {
-- 
2.20.1