Re: [PATCH] target/i386: Avoid cpu number overflow in legacy topology

[Zhao Liu <zhao1.liu@linux.intel.com>]

On Fri, Jul 28, 2023 at 04:01:50PM +0800, Qian Wen wrote:
> Date: Fri, 28 Jul 2023 16:01:50 +0800
> From: Qian Wen <qian.wen@intel.com>
> Subject: [PATCH] target/i386: Avoid cpu number overflow in legacy topology
> X-Mailer: git-send-email 2.25.1
> 
> 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.
> 
> 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.
> +         */
> +        threads_per_socket = cs->nr_cores * cs->nr_threads;
> +        if (threads_per_socket > 255) {
> +            threads_per_socket = 255;

Straight encoding to 255 is good for me!

-Zhao

> +        }
> +
> +        if (threads_per_socket > 1) {
> +            *ebx |= threads_per_socket << 16;
>              *edx |= CPUID_HT;
>          }
>          /*
> -- 
> 2.25.1
>