Date:   Fri, 15 Jan 2021 11:10:55 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Baoquan He <bhe@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>, Qian Cai <cai@....pw>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org
Subject: Re: [PATCH 1/2] x86/setup: consolidate early memory reservations

On 15.01.21 09:32, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> The early reservations of memory areas used by the firmware, bootloader,
> kernel text and data are spread over setup_arch(). Moreover, some of them
> happen *after* memblock allocations, e.g trim_platform_memory_ranges() and
> trim_low_memory_range() are called after reserve_real_mode() that allocates
> memory.
> 
> We did not observe corruption of these memory regions because memblock
> always allocates memory either from the end of memory (in top-down mode) or
> above the kernel image (in bottom-up mode). However, the bottom up mode is
> going to be updated to span the entire memory [1] to avoid limitations
> caused by KASLR.
> 
> Consolidate early memory reservations in a dedicated function to improve
> robustness against future changes. Having the early reservations in one
> place also makes it clearer what memory must be reserved before we allow
> memblock allocations.
> 
> [1] https://lore.kernel.org/lkml/20201217201214.3414100-2-guro@fb.com
> 
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> ---
>  arch/x86/kernel/setup.c | 80 ++++++++++++++++++++++-------------------
>  1 file changed, 44 insertions(+), 36 deletions(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 3412c4595efd..32cd2e790a0a 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -728,7 +728,38 @@ static void __init trim_low_memory_range(void)
>  	 */
>  	memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
>  }
> -	
> +
> +static void __init early_reserve_memory(void)
> +{
> +	/*
> +	 * Reserve the memory occupied by the kernel between _text and
> +	 * __end_of_kernel_reserve symbols. Any kernel sections after the
> +	 * __end_of_kernel_reserve symbol must be explicitly reserved with a
> +	 * separate memblock_reserve() or they will be discarded.
> +	 */
> +	memblock_reserve(__pa_symbol(_text),
> +			 (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
> +
> +	/*
> +	 * Make sure page 0 is always reserved because on systems with
> +	 * L1TF its contents can be leaked to user processes.
> +	 */
> +	memblock_reserve(0, PAGE_SIZE);
> +
> +	early_reserve_initrd();
> +
> +	if (efi_enabled(EFI_BOOT))
> +		efi_memblock_x86_reserve_range();
> +
> +	memblock_x86_reserve_range_setup_data();
> +
> +	reserve_ibft_region();
> +	reserve_bios_regions();
> +
> +	trim_platform_memory_ranges();
> +	trim_low_memory_range();
> +}
> +
>  /*
>   * Dump out kernel offset information on panic.
>   */
> @@ -763,29 +794,6 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
>  
>  void __init setup_arch(char **cmdline_p)
>  {
> -	/*
> -	 * Reserve the memory occupied by the kernel between _text and
> -	 * __end_of_kernel_reserve symbols. Any kernel sections after the
> -	 * __end_of_kernel_reserve symbol must be explicitly reserved with a
> -	 * separate memblock_reserve() or they will be discarded.
> -	 */
> -	memblock_reserve(__pa_symbol(_text),
> -			 (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
> -
> -	/*
> -	 * Make sure page 0 is always reserved because on systems with
> -	 * L1TF its contents can be leaked to user processes.
> -	 */
> -	memblock_reserve(0, PAGE_SIZE);
> -
> -	early_reserve_initrd();
> -
> -	/*
> -	 * At this point everything still needed from the boot loader
> -	 * or BIOS or kernel text should be early reserved or marked not
> -	 * RAM in e820. All other memory is free game.
> -	 */
> -
>  #ifdef CONFIG_X86_32
>  	memcpy(&boot_cpu_data, &new_cpu_data, sizeof(new_cpu_data));
>  
> @@ -909,8 +917,18 @@ void __init setup_arch(char **cmdline_p)
>  
>  	parse_early_param();
>  
> -	if (efi_enabled(EFI_BOOT))
> -		efi_memblock_x86_reserve_range();
> +	/*
> +	 * 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
> @@ -937,9 +955,6 @@ void __init setup_arch(char **cmdline_p)
>  
>  	x86_report_nx();
>  
> -	/* after early param, so could get panic from serial */
> -	memblock_x86_reserve_range_setup_data();
> -
>  	if (acpi_mps_check()) {
>  #ifdef CONFIG_X86_LOCAL_APIC
>  		disable_apic = 1;
> @@ -1031,8 +1046,6 @@ void __init setup_arch(char **cmdline_p)
>  	 */
>  	find_smp_config();
>  
> -	reserve_ibft_region();
> -
>  	early_alloc_pgt_buf();
>  
>  	/*
> @@ -1053,8 +1066,6 @@ void __init setup_arch(char **cmdline_p)
>  	 */
>  	sev_setup_arch();
>  
> -	reserve_bios_regions();
> -
>  	efi_fake_memmap();
>  	efi_find_mirror();
>  	efi_esrt_init();
> @@ -1080,9 +1091,6 @@ void __init setup_arch(char **cmdline_p)
>  
>  	reserve_real_mode();
>  
> -	trim_platform_memory_ranges();
> -	trim_low_memory_range();
> -
>  	init_mem_mapping();
>  
>  	idt_setup_early_pf();
> 

Did not fully review for side-effects, but looks like a reasonable thing
to do!

-- 
Thanks,

David / dhildenb

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