From: David Hildenbrand <david@redhat.com>
To: Mike Rapoport <rppt@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Cc: "Andrea Arcangeli" <aarcange@redhat.com>,
"Baoquan He" <bhe@redhat.com>, "Borislav Petkov" <bp@alien8.de>,
"Chris Wilson" <chris@chris-wilson.co.uk>,
"H. Peter Anvin" <hpa@zytor.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Łukasz Majczak" <lma@semihalf.com>,
"Mel Gorman" <mgorman@suse.de>,
"Michal Hocko" <mhocko@kernel.org>,
"Mike Rapoport" <rppt@linux.ibm.com>, "Qian Cai" <cai@lca.pw>,
"Sarvela, Tomi P" <tomi.p.sarvela@intel.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Vlastimil Babka" <vbabka@suse.cz>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
stable@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH v4 1/2] x86/setup: always add the beginning of RAM as memblock.memory
Date: Mon, 1 Feb 2021 10:32:44 +0100 [thread overview]
Message-ID: <56e2c568-b121-8860-a6b0-274ace46d835@redhat.com> (raw)
In-Reply-To: <20210130221035.4169-2-rppt@kernel.org>
On 30.01.21 23:10, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> The physical memory on an x86 system starts at address 0, but this is not
> always reflected in e820 map. For example, the BIOS can have e820 entries
> like
>
> [ 0.000000] BIOS-provided physical RAM map:
> [ 0.000000] BIOS-e820: [mem 0x0000000000001000-0x000000000009ffff] usable
>
> or
>
> [ 0.000000] BIOS-provided physical RAM map:
> [ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x0000000000000fff] reserved
> [ 0.000000] BIOS-e820: [mem 0x0000000000001000-0x0000000000057fff] usable
>
> In either case, e820__memblock_setup() won't add the range 0x0000 - 0x1000
> to memblock.memory and later during memory map initialization this range is
> left outside any zone.
>
> With SPARSEMEM=y there is always a struct page for pfn 0 and this struct
> page will have it's zone link wrong no matter what value will be set there.
>
> To avoid this inconsistency, add the beginning of RAM to memblock.memory.
> Limit the added chunk size to match the reserved memory to avoid
> registering memory that may be used by the firmware but never reserved at
> e820__memblock_setup() time.
>
> Fixes: bde9cfa3afe4 ("x86/setup: don't remove E820_TYPE_RAM for pfn 0")
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> Cc: stable@vger.kernel.org
> ---
> arch/x86/kernel/setup.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 3412c4595efd..67c77ed6eef8 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -727,6 +727,14 @@ static void __init trim_low_memory_range(void)
> * Kconfig help text for X86_RESERVE_LOW.
> */
> memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
> +
> + /*
> + * Even if the firmware does not report the memory at address 0 as
> + * usable, inform the generic memory management about its existence
> + * to ensure it is a part of ZONE_DMA and the memory map for it is
> + * properly initialized.
> + */
> + memblock_add(0, ALIGN(reserve_low, PAGE_SIZE));
> }
>
> /*
>
I think, to make that code more robust, and to not rely on archs to do
the right thing, we should do something like
1) Make sure in free_area_init() that each PFN with a memmap (i.e.,
falls into a partial present section) is spanned by a zone; that would
include PFN 0 in this case.
2) In init_zone_unavailable_mem(), similar to round_up(max_pfn,
PAGES_PER_SECTION) handling, consider range
[round_down(min_pfn, PAGES_PER_SECTION), min_pfn - 1]
which would handle in the x86-64 case [0..0] and, therefore, initialize
PFN 0.
Also, I think the special-case of PFN 0 is analogous to the
round_up(max_pfn, PAGES_PER_SECTION) handling in
init_zone_unavailable_mem(): who guarantees that these PFN above the
highest present PFN are actually spanned by a zone?
I'd suggest going through all zone ranges in free_area_init() first,
dealing with zones that have "not section aligned start/end", clamping
them up/down if required such that no holes within a section are left
uncovered by a zone.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-02-01 9:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-30 22:10 [PATCH v4 0/2] mm: fix initialization of struct page for holes in memory layout Mike Rapoport
2021-01-30 22:10 ` [PATCH v4 1/2] x86/setup: always add the beginning of RAM as memblock.memory Mike Rapoport
2021-01-31 0:37 ` Linus Torvalds
2021-01-31 8:03 ` Mike Rapoport
2021-01-31 21:49 ` Linus Torvalds
2021-02-01 14:06 ` Mike Rapoport
2021-02-01 9:32 ` David Hildenbrand [this message]
2021-02-01 11:26 ` Baoquan He
2021-02-01 14:34 ` Mike Rapoport
2021-02-01 14:55 ` Baoquan He
2021-02-01 14:30 ` Mike Rapoport
2021-02-01 14:32 ` David Hildenbrand
2021-02-01 23:22 ` Mike Rapoport
2021-01-30 22:10 ` [PATCH v4 2/2] mm: fix initialization of struct page for holes in memory layout Mike Rapoport
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