linux-kernel - Re: [PATCH v4 07/12] x86/mtrr: allocate mtrr

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Date:   Mon, 20 Mar 2023 12:25:01 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "Gross, Jurgen" <jgross@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 07/12] x86/mtrr: allocate mtrr_value array dynamically

On Mon, 2023-03-06 at 17:34 +0100, Juergen Gross wrote:
> The mtrr_value[] array is a static variable, which is used only in a
> few configurations. Consuming 6kB is ridiculous for this case,
> especially as the array doesn't need to be that large and it can easily
> be allocated dynamically.
> 
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  arch/x86/kernel/cpu/mtrr/mtrr.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/mtrr/mtrr.c b/arch/x86/kernel/cpu/mtrr/mtrr.c
> index 0c83990501f5..50cd2287b6e1 100644
> --- a/arch/x86/kernel/cpu/mtrr/mtrr.c
> +++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
> @@ -581,7 +581,7 @@ struct mtrr_value {
>  	unsigned long	lsize;
>  };
>  
> -static struct mtrr_value mtrr_value[MTRR_MAX_VAR_RANGES];
> +static struct mtrr_value *mtrr_value;
>  
>  static int mtrr_save(void)
>  {
> @@ -750,6 +750,7 @@ static int __init mtrr_init_finialize(void)
>  	 * TBD: is there any system with such CPU which supports
>  	 * suspend/resume? If no, we should remove the code.
>  	 */
> +	mtrr_value = kcalloc(num_var_ranges, sizeof(*mtrr_value), GFP_KERNEL);

Theoretically dynamic allocation can fail, although it should not happen as this
happens during kernel boot and the size is small.  Maybe a WARN()?

>  	register_syscore_ops(&mtrr_syscore_ops);
>  
>  	return 0;