Re: [PATCH] i386/cpu: Don't emulate L3 cache on 8000_001D if l3-cache is disabled

[wangyanan (Y)]

在 2023/6/2 14:52, Xiaoyao Li 写道:
> On 5/31/2023 8:00 PM, Yanan Wang wrote:
> > Currently, we only avoid emulating L3 cache properties for AMD CPU
> > when l3-cache is off, but failed to consider this case on CPUID 
> > 8000_001D.
> > This result in a fact that we will still have L3 caches in the VM
> > although we pass "host-cache-info=off,l3-cache=off" CLI to qemu.
>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Thanks.
> Out of curiosity, do you have a valid real use case to run VM with 
> "l3-cache = off"?
No, actually. This problem is found just in testing.

Yanan.
> > Fixes: 8f4202fb108 ("i386: Populate AMD Processor Cache Information 
> > for cpuid 0x8000001D")
> > Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
> > ---
> >   target/i386/cpu.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > index 1242bd541a..17c367c5ba 100644
> > --- a/target/i386/cpu.c
> > +++ b/target/i386/cpu.c
> > @@ -6337,8 +6337,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t 
> > index, uint32_t count,
> >                                          &topo_info, eax, ebx, ecx, 
> > edx);
> >               break;
> >           case 3: /* L3 cache info */
> > - encode_cache_cpuid8000001d(env->cache_info_amd.l3_cache,
> > -                                       &topo_info, eax, ebx, ecx, edx);
> > +            if (cpu->enable_l3_cache) {
> > + encode_cache_cpuid8000001d(env->cache_info_amd.l3_cache,
> > +                                           &topo_info, eax, ebx, 
> > ecx, edx);
> > +            }
> >               break;
> >           default: /* end of info */
> >               *eax = *ebx = *ecx = *edx = 0;