linux-kernel - Re: [PATCH 2/2] x86/setup: merge several reservations of start of the memory

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Date:   Mon, 25 Jan 2021 15:55:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Baoquan He <bhe@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        "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 2/2] x86/setup: merge several reservations of start of
 the memory

On Fri, Jan 15, 2021 at 10:32:55AM +0200, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> Currently the first several pages are reserved both to avoid leaking their
> contents on systems with L1TF and to avoid corrupting BIOS memory.
> 
> Merge the two memory reservations.
> 
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> ---
>  arch/x86/kernel/setup.c | 29 +++++++++++------------------
>  1 file changed, 11 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 32cd2e790a0a..3f2fd67240f8 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -715,20 +715,6 @@ static int __init parse_reservelow(char *p)
>  
>  early_param("reservelow", parse_reservelow);
>  
> -static void __init trim_low_memory_range(void)
> -{
> -	/*
> -	 * A special case is the first 4Kb of memory;
> -	 * This is a BIOS owned area, not kernel ram, but generally
> -	 * not listed as such in the E820 table.
> -	 *
> -	 * This typically reserves additional memory (64KiB by default)
> -	 * since some BIOSes are known to corrupt low memory.  See the
> -	 * Kconfig help text for X86_RESERVE_LOW.
> -	 */
> -	memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
> -}
> -
>  static void __init early_reserve_memory(void)
>  {
>  	/*
> @@ -741,10 +727,18 @@ static void __init early_reserve_memory(void)
>  			 (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.
> +	 * The first 4Kb of memory is a BIOS owned area, but generally it is
> +	 * not listed as such in the E820 table.
> +	 *
> +	 * Reserve the first memory page and typically some additional
> +	 * memory (64KiB by default) since some BIOSes are known to corrupt
> +	 * low memory. See the Kconfig help text for X86_RESERVE_LOW.
> +	 *
> +	 * In addition, we must make sure page 0 is always reserved because

s/we must//

Other than that:

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

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