Re: [PATCH v3 2/2] target/i386: Avoid overflow of the cache parameter enumerated by leaf 4

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 8/16/2023 4:06 PM, Qian Wen wrote:
> According to SDM, CPUID.0x4:EAX[31:26] indicates the Maximum number of
> addressable IDs for processor cores in the physical package. If we
> launch over 64 cores VM, the 6-bit field will overflow, and the wrong
> core_id number will be reported.
> 
> Since the HW reports 0x3f when the intel processor has over 64 cores,
> limit the max value written to EBX[31:26] to 63, so max num_cores should
> be 64.
> 
> Signed-off-by: Qian Wen <qian.wen@intel.com>
> Reviewed-by: Zhao Liu <zhao1.liu@intel.com>

Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.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 5c008b9d7e..3b6854300a 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -248,7 +248,7 @@ static void encode_cache_cpuid4(CPUCacheInfo *cache,
>       *eax = CACHE_TYPE(cache->type) |
>              CACHE_LEVEL(cache->level) |
>              (cache->self_init ? CACHE_SELF_INIT_LEVEL : 0) |
> -           ((num_cores - 1) << 26) |
> +           ((MIN(num_cores, 64) - 1) << 26) |
>              ((num_apic_ids - 1) << 14);
>   
>       assert(cache->line_size > 0);