Re: [PATCH v4 07/12] x86/mtrr: allocate mtrr_value array dynamically

From: Borislav Petkov
Date: Sun Mar 26 2023 - 18:05:32 EST


On Mon, Mar 06, 2023 at 05:34:20PM +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,

Ah, that struct mtrr_value is of size 24 due to that first member
mtrr_type getting padded even if it is a u8.

> especially as the array doesn't need to be that large and it can easily
> be allocated dynamically.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> 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);

Pls put that over the comment.

Also, you need to handle kcalloc() returning an error.

--
Regards/Gruss,
Boris.

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