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
On Intel platform:
CPUID.01H.EBX[23:16] is defined as "max number of addressable IDs for
logical processors in the physical package".
When executing "cpuid -1 -l 1 -r" in the guest, we obtain a value of 90 for
CPUID.01H.EBX[23:16], whereas the expected value is 128. Additionally,
executing "cpuid -1 -l 4 -r" in the guest yields a value of 63 for
CPUID.04H.EAX[31:26], which matches the expected result.
As (1+CPUID.04H.EAX[31:26]) rounds 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 threads-per-core should actually be 2.
And on AMD platform:
CPUID.01H.EBX[23:16] is defined as "Logical processor count". Current
result meets our expectation.
So let us round up CPUID.01H.EBX[23:16] to the nearest power-of-2 integer
only for Intel platform to solve the unexpected result.
Reviewed-by: Zhao Liu <zhao1....@intel.com>
Acked-by: Igor Mammedov <imamm...@redhat.com>
Signed-off-by: Guixiong Wei <weiguixi...@bytedance.com>
Signed-off-by: Yipeng Yin <yinyip...@bytedance.com>
Signed-off-by: Chuang Xu <xuchuangxc...@bytedance.com>
---
target/i386/cpu.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index ff227a8c5c..641d4577b0 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6462,7 +6462,15 @@ 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;
+ /*
+ * AMD requires logical processor count, but Intel needs maximum
+ * number of addressable IDs for logical processors per package.
+ */
+ if (cpu->vendor_cpuid_only && IS_AMD_CPU(env)) {
+ *ebx |= threads_per_pkg << 16;
+ } else {
+ *ebx |= 1 << apicid_pkg_offset(&topo_info) << 16;
+ }
*edx |= CPUID_HT;
}
if (!cpu->enable_pmu) {
--
2.20.1
