Re: [PATCH v6 35/60] i386/cpu: Introduce enable_cpuid_0x1f to force exposing CPUID 0x1f

Ira Weiny
2024-12-12T22:16:33Z

On Tue, Nov 05, 2024 at 01:23:43AM -0500, Xiaoyao Li wrote:
> Currently, QEMU exposes CPUID 0x1f to guest only when necessary, i.e.,
> when topology level that cannot be enumerated by leaf 0xB, e.g., die or
> module level, are configured for the guest, e.g., -smp xx,dies=2.
>
> However, TDX architecture forces to require CPUID 0x1f to configure CPU
> topology.
>
> Introduce a bool flag, enable_cpuid_0x1f, in CPU for the case that
> requires CPUID leaf 0x1f to be exposed to guest.
>
> Introduce a new function x86_has_cpuid_0x1f(), which is the warpper of
> cpu->enable_cpuid_0x1f and x86_has_extended_topo() to check if it needs
> to enable cpuid leaf 0x1f for the guest.

Could you elaborate on the relation between cpuid_0x1f and the extended
topology support? I feel like x86_has_cpuid_0x1f() is a poor name for this
check.

Perhaps I'm just not understanding what is required here?

Ira

>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
> target/i386/cpu.c | 4 ++--
> target/i386/cpu.h | 9 +++++++++
> target/i386/kvm/kvm.c | 2 +-
> 3 files changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 1ffbafef03e7..119b38bcb0c1 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -6731,7 +6731,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
> break;
> case 0x1F:
> /* V2 Extended Topology Enumeration Leaf */
> - if (!x86_has_extended_topo(env->avail_cpu_topo)) {
> + if (!x86_has_cpuid_0x1f(cpu)) {
> *eax = *ebx = *ecx = *edx = 0;
> break;
> }
> @@ -7588,7 +7588,7 @@ void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
> * cpu->vendor_cpuid_only has been unset for compatibility with older
> * machine types.
> */
> - if (x86_has_extended_topo(env->avail_cpu_topo) &&
> + if (x86_has_cpuid_0x1f(cpu) &&
> (IS_INTEL_CPU(env) || !cpu->vendor_cpuid_only)) {
> x86_cpu_adjust_level(cpu, &env->cpuid_min_level, 0x1F);
> }
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index 59959b8b7a4d..dcc673262c06 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -2171,6 +2171,9 @@ struct ArchCPU {
> /* Compatibility bits for old machine types: */
> bool enable_cpuid_0xb;
>
> + /* Force to enable cpuid 0x1f */
> + bool enable_cpuid_0x1f;
> +
> /* Enable auto level-increase for all CPUID leaves */
> bool full_cpuid_auto_level;
>
> @@ -2431,6 +2434,12 @@ void host_cpuid(uint32_t function, uint32_t count,
> uint32_t *eax, uint32_t *ebx, uint32_t *ecx, uint32_t *edx);
> bool cpu_has_x2apic_feature(CPUX86State *env);
>
> +static inline bool x86_has_cpuid_0x1f(X86CPU *cpu)
> +{
> + return cpu->enable_cpuid_0x1f ||
> + x86_has_extended_topo(cpu->env.avail_cpu_topo);
> +}
> +
> /* helper.c */
> void x86_cpu_set_a20(X86CPU *cpu, int a20_state);
> void cpu_sync_avx_hflag(CPUX86State *env);
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index dea0f83370d5..022809bad36e 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -1874,7 +1874,7 @@ uint32_t kvm_x86_build_cpuid(CPUX86State *env, struct kvm_cpuid_entry2 *entries,
> break;
> }
> case 0x1f:
> - if (!x86_has_extended_topo(env->avail_cpu_topo)) {
> + if (!x86_has_cpuid_0x1f(env_archcpu(env))) {
> cpuid_i--;
> break;
> }
> --
> 2.34.1
>