From: Mike Rapoport <rppt@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
Baoquan He <bhe@redhat.com>, Borislav Petkov <bp@alien8.de>,
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@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: [PATCH v3 1/2] x86/setup: don't remove E820_TYPE_RAM for pfn 0
Date: Mon, 11 Jan 2021 21:40:16 +0200 [thread overview]
Message-ID: <20210111194017.22696-2-rppt@kernel.org> (raw)
In-Reply-To: <20210111194017.22696-1-rppt@kernel.org>
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(-)
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 740f3bdb3f61..3412c4595efd 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -660,17 +660,6 @@ static void __init trim_platform_memory_ranges(void)
static void __init trim_bios_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.
- */
- e820__range_update(0, PAGE_SIZE, E820_TYPE_RAM, E820_TYPE_RESERVED);
-
/*
* special case: Some BIOSes report the PC BIOS
* area (640Kb -> 1Mb) as RAM even though it is not.
@@ -728,6 +717,15 @@ 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));
}
--
2.28.0
next prev parent reply other threads:[~2021-01-11 19:40 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 ` Mike Rapoport [this message]
2021-01-13 8:56 ` [PATCH v3 1/2] x86/setup: don't remove E820_TYPE_RAM for pfn 0 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
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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