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Re: [Qemu-devel] [PATCH v3 7/9] target/i386: Support multi-dies when hos


From: Eduardo Habkost
Subject: Re: [Qemu-devel] [PATCH v3 7/9] target/i386: Support multi-dies when host doesn't support CPUID.1F
Date: Wed, 19 Jun 2019 16:15:46 -0300

On Wed, Jun 12, 2019 at 04:41:02PM +0800, Like Xu wrote:
> In guest CPUID generation process, the cpuid_min_level would be adjusted to
> the maximum passed value for basic CPUID configuration and it should not be
> restricted by the limited value returned from cpu_x86_cpuid(). After the basic
> cpu_x86_cpuid() loop is finished, the cpuid_0_entry.eax needs to be configured
> again by the last adjusted cpuid_min_level value.
> 
> If a user wants to expose CPUID.1F by passing dies > 1 for any reason without
> host support, a per-cpu smp topology warning will appear but it's not blocked.
> 
> Signed-off-by: Like Xu <address@hidden>

This code doesn't look at host CPUID at all, as far as I can see.
Isn't it simpler to just make cpuid_x86_cpuid() return the
correct data?

> ---
>  target/i386/kvm.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 9b4da9b265..8bf1604d2b 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -931,12 +931,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      struct kvm_cpuid_entry2 *c;
>      uint32_t signature[3];
>      int kvm_base = KVM_CPUID_SIGNATURE;
> -    int r;
> +    int r, cpuid_0_entry, cpuid_min_level;
>      Error *local_err = NULL;
>  
>      memset(&cpuid_data, 0, sizeof(cpuid_data));
>  
> -    cpuid_i = 0;
> +    cpuid_i = cpuid_0_entry = cpuid_min_level = 0;
>  
>      r = kvm_arch_set_tsc_khz(cs);
>      if (r < 0) {
> @@ -1050,6 +1050,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
>  
>      cpu_x86_cpuid(env, 0, 0, &limit, &unused, &unused, &unused);
>  
> +    /* Allow 0x1f setting regardless of kvm support if nr_dies > 1 */
> +    if (limit < 0x1f && env->nr_dies > 1 && cpu->enable_cpuid_0x1f) {
> +        limit = env->cpuid_level = env->cpuid_min_level = 0x1f;
> +        warn_report("CPU topology: the CPUID.1F isn't supported on the 
> host.");
> +    }
> +
>      for (i = 0; i <= limit; i++) {
>          if (cpuid_i == KVM_MAX_CPUID_ENTRIES) {
>              fprintf(stderr, "unsupported level value: 0x%x\n", limit);
> @@ -1151,8 +1157,22 @@ int kvm_arch_init_vcpu(CPUState *cs)
>              cpu_x86_cpuid(env, i, 0, &c->eax, &c->ebx, &c->ecx, &c->edx);
>              break;
>          }
> +
> +        /* Remember the index of cpuid.0 leaf for reconfiguration. */
> +        cpuid_0_entry = (i == 0) ? (cpuid_i - 1) : cpuid_0_entry;
> +
> +        /* Adjust cpuid_min_level to the maximum index of valid basic 
> cpuids. */
> +        cpuid_min_level =
> +                ((c->eax | c->ebx | c->ecx | c->edx | c->flags | c->index) &&
> +                                (i > cpuid_min_level)) ? i : cpuid_min_level;
>      }
>  
> +    env->cpuid_level = env->cpuid_min_level = cpuid_min_level;
> +
> +    /* Reconfigure cpuid_0_eax value to follow CPUID.0 instruction spec.*/
> +    c = &cpuid_data.entries[cpuid_0_entry];
> +    cpu_x86_cpuid(env, 0, 0, &c->eax, &c->ebx, &c->ecx, &c->edx);
> +
>      if (limit >= 0x0a) {
>          uint32_t eax, edx;
>  
> -- 
> 2.21.0
> 

-- 
Eduardo



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