|
On 8/7/2023 3:36 PM, Xiaoyao Li wrote:
On
7/28/2023 4:01 PM, Qian Wen wrote:
The legacy topology enumerated by
CPUID.1.EBX[23:16] is defined in SDM
Vol2:
Bits 23-16: Maximum number of addressable IDs for logical
processors in
this physical package.
To avoid data overflow, limit the max value written to
EBX[23:16] to
255.
It's better explain what's issue when overflow happens.
When launch vm with -smp 256, the value writes to EBX[23:16] is 0.
If the guest only support legacy topology, the result of kernel
invokes cpu_smt_allowed() is false and AP's bring-up will fail. Then
only CPU 0 is online, others offline.
Signed-off-by: Qian Wen
<qian.wen@intel.com>
---
target/i386/cpu.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 1294be374ab2..70589a58b727 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5356,6 +5356,7 @@ void cpu_x86_cpuid(CPUX86State *env,
uint32_t index, uint32_t count,
uint32_t die_offset;
uint32_t limit;
uint32_t signature[3];
+ uint32_t threads_per_socket;
X86CPUTopoInfo topo_info;
topo_info.dies_per_pkg = env->nr_dies;
@@ -5397,8 +5398,18 @@ void cpu_x86_cpuid(CPUX86State *env,
uint32_t index, uint32_t count,
*ecx |= CPUID_EXT_OSXSAVE;
}
*edx = env->features[FEAT_1_EDX];
- if (cs->nr_cores * cs->nr_threads > 1) {
- *ebx |= (cs->nr_cores * cs->nr_threads)
<< 16;
+ /*
+ * The vCPU number more than 255 needs support of V2
Extended
+ * Topology enumerated by CPUID.0x1f or Extended
Topology
+ * enumerated by CPUID.0x0b.
+ */
the above comment doesn't explain why it needs below.
you can explain only bits [23:16] represents the maximum number of
addressable IDs for logical processors in this physical package.
When thread_per_socket > 255, it will 1) overwrite bits[31:24]
which is apic_id, 2) bits [23:16] gets truncated.
Thanks for your suggestion, I will add your description in v2.
Thanks,
Qian
+ threads_per_socket =
cs->nr_cores * cs->nr_threads;
+ if (threads_per_socket > 255) {
+ threads_per_socket = 255;
+ }
+
+ if (threads_per_socket > 1) {
+ *ebx |= threads_per_socket << 16;
*edx |= CPUID_HT;
}
/*
|