diff mbox series

[v4] i386/cpu: fixup number of addressable IDs for logical processors in the physical package

Message ID 20241007081344.10907-1-xuchuangxclwt@bytedance.com
State New
Headers show
Series [v4] i386/cpu: fixup number of addressable IDs for logical processors in the physical package | expand

Commit Message

Chuang Xu Oct. 7, 2024, 8:13 a.m. UTC 
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

Try to execute "cpuid -1 -l 1 -r" in guest, we'll obtain a value of 90 for
CPUID.01H.EBX[23:16], while the expected value is 128. And Try to
execute "cpuid -1 -l 4 -r" in guest, we'll obtain a value of 63 for
CPUID.04H.EAX[31:26] 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.

In addition, we introduce max_thread_number_in_package() instead of
using pow2ceil() to be compatible with smp and hybrid.

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 mbox series

Patch

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 85ef7452c0..1b4e3b6931 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) -
@@ -6462,7 +6468,7 @@  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) {