On Wed, 18 Sep 2024 21:18:15 +0800 Chuang Xu <xuchuangxc...@bytedance.com> wrote:
> 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. > > Signed-off-by: Guixiong Wei <weiguixi...@bytedance.com> > Signed-off-by: Yipeng Yin <yinyip...@bytedance.com> > Signed-off-by: Chuang Xu <xuchuangxc...@bytedance.com> Reviewed-by: Igor Mammedov <imamm...@redhat.com> > --- > target/i386/cpu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c > index 4c2e6f3a71..3710ae5283 100644 > --- a/target/i386/cpu.c > +++ b/target/i386/cpu.c > @@ -6417,7 +6417,7 @@ 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 |= pow2ceil(threads_per_pkg) << 16; > *edx |= CPUID_HT; > } > if (!cpu->enable_pmu) {