Re: [PATCH v5 02/10] x86/resctrl: Protect against bad shift

[Borislav Petkov]

On Tue, Jun 30, 2026 at 09:27:02PM -0700, Reinette Chatre wrote:
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index bca782050198..9b9495174041 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -247,7 +247,11 @@ static __init bool __rdt_get_mem_config_amd(struct rdt_resource *r)
>  
>  	cpuid_count(0x80000020, subleaf, &eax, &ebx, &ecx, &edx);
>  	hw_res->num_closid = edx + 1;
> -	r->membw.max_bw = 1 << eax;
> +	if (BITS_PER_TYPE(r->membw.max_bw) <= eax) {
> +		pr_warn("Unable to support hardware's maximum bandwidth\n");
> +		return false;
> +	}
> +	r->membw.max_bw = BIT(eax);

Why?

Why go all the effort if the field can be 64 bits?

Why not make max_bw u64 and handle *all* possible values naturally?

-- 
Regards/Gruss,
    Boris.

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