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From: Borislav Petkov <bp@alien8.de>
To: Mike Rapoport <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Baoquan He <bhe@redhat.com>, David Hildenbrand <david@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>,
	Mike Rapoport <rppt@linux.ibm.com>, Qian Cai <cai@lca.pw>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org
Subject: Re: [PATCH v3 1/2] x86/setup: don't remove E820_TYPE_RAM for pfn 0
Date: Thu, 21 Jan 2021 14:25:42 +0100	[thread overview]
Message-ID: <20210121132542.GB32060@zn.tnic> (raw)
In-Reply-To: <20210111194017.22696-2-rppt@kernel.org>

On Mon, Jan 11, 2021 at 09:40:16PM +0200, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
> 
> The first 4Kb of memory is a BIOS owned area and to avoid its allocation
> for the kernel it was not listed in e820 tables as memory. As the result,
> pfn 0 was never recognised by the generic memory management and it is not a
> part of neither node 0 nor ZONE_DMA.
> 
> If set_pfnblock_flags_mask() would be ever called for the pageblock
> corresponding to the first 2Mbytes of memory, having pfn 0 outside of
> ZONE_DMA would trigger
> 
> 	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
> 
> Along with reserving the first 4Kb in e820 tables, several first pages are
> reserved with memblock in several places during setup_arch(). These
> reservations are enough to ensure the kernel does not touch the BIOS area
> and it is not necessary to remove E820_TYPE_RAM for pfn 0.
> 
> Remove the update of e820 table that changes the type of pfn 0 and move the
> comment describing why it was done to trim_low_memory_range() that reserves
> the beginning of the memory.
> 
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
>  arch/x86/kernel/setup.c | 20 +++++++++-----------
>  1 file changed, 9 insertions(+), 11 deletions(-)

FWIW,

Acked-by: Borislav Petkov <bp@suse.de>

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette


  parent reply	other threads:[~2021-01-21 13:25 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-11 19:40 [PATCH v3 0/2] mm: fix initialization of struct page for holes in memory layout Mike Rapoport
2021-01-11 19:40 ` [PATCH v3 1/2] x86/setup: don't remove E820_TYPE_RAM for pfn 0 Mike Rapoport
2021-01-13  8:56   ` Oscar Salvador
2021-01-13 11:23     ` Mike Rapoport
2021-01-13 12:56   ` David Hildenbrand
2021-01-13 15:35     ` Mike Rapoport
2021-01-21 13:25   ` Borislav Petkov [this message]
2021-01-11 19:40 ` [PATCH v3 2/2] mm: fix initialization of struct page for holes in memory layout Mike Rapoport
2021-02-01  9:14   ` David Hildenbrand
2021-02-01  9:39     ` Baoquan He
2021-02-01 14:12       ` Mike Rapoport
2021-01-12  0:58 ` [PATCH v3 0/2] " Andrew Morton
2021-01-12  5:25   ` Mike Rapoport

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