Re: [PATCH] x86/setup: call early_reserve_memory() earlier

[Jan Beulich]

On 14.09.2021 11:41, Juergen Gross wrote:
> Commit a799c2bd29d19c565 ("x86/setup: Consolidate early memory
> reservations") introduced early_reserve_memory() to do all needed
> initial memblock_reserve() calls in one function. Unfortunately the
> call of early_reserve_memory() is done too late for Xen dom0, as in
> some cases a Xen hook called by e820__memory_setup() will need those
> memory reservations to have happened already.
> 
> Move the call of early_reserve_memory() to the beginning of
> setup_arch() in order to avoid such problems.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: a799c2bd29d19c565 ("x86/setup: Consolidate early memory reservations")
> Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  arch/x86/kernel/setup.c | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 79f164141116..f369c51ec580 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -757,6 +757,18 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
>  
>  void __init setup_arch(char **cmdline_p)
>  {
> +	/*
> +	 * Do some memory reservations *before* memory is added to
> +	 * memblock, so memblock allocations won't overwrite it.
> +	 * Do it after early param, so we could get (unlikely) panic from
> +	 * serial.

Hmm, this part of the comment is not only stale now, but gets actively
undermined. No idea how likely such a panic() would be, and hence how
relevant it is to retain this particular property.

Jan

> +	 * After this point everything still needed from the boot loader or
> +	 * firmware or kernel text should be early reserved or marked not
> +	 * RAM in e820. All other memory is free game.
> +	 */
> +	early_reserve_memory();
> +
>  #ifdef CONFIG_X86_32
>  	memcpy(&boot_cpu_data, &new_cpu_data, sizeof(new_cpu_data));
>  
> @@ -876,18 +888,6 @@ void __init setup_arch(char **cmdline_p)
>  
>  	parse_early_param();
>  
> -	/*
> -	 * Do some memory reservations *before* memory is added to
> -	 * memblock, so memblock allocations won't overwrite it.
> -	 * Do it after early param, so we could get (unlikely) panic from
> -	 * serial.
> -	 *
> -	 * After this point everything still needed from the boot loader or
> -	 * firmware or kernel text should be early reserved or marked not
> -	 * RAM in e820. All other memory is free game.
> -	 */
> -	early_reserve_memory();
> -
>  #ifdef CONFIG_MEMORY_HOTPLUG
>  	/*
>  	 * Memory used by the kernel cannot be hot-removed because Linux
>