[tip:x86/mm] x86, mm: Move reserving low memory later in initialization

[tip:x86/mm] x86, mm: Move reserving low memory later in initialization

[tip-bot for H. Peter Anvin]

Commit-ID:  95c9608478d639dcffc14ea47b31bff021a99ed1
Gitweb:     http://git.kernel.org/tip/95c9608478d639dcffc14ea47b31bff021a99ed1
Author:     H. Peter Anvin <hpa@zytor.com>
AuthorDate: Thu, 14 Feb 2013 14:02:52 -0800
Committer:  H. Peter Anvin <hpa@zytor.com>
CommitDate: Thu, 14 Feb 2013 15:21:25 -0800

x86, mm: Move reserving low memory later in initialization

Move the reservation of low memory, except for the 4K which actually
does belong to the BIOS, later in the initialization; in particular,
after we have already reserved the trampoline.

The current code locates the trampoline as high as possible, so by
deferring the allocation we will still be able to reserve as much
memory as is possible.  This allows us to run with reservelow=640k
without getting a crash on system startup.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Link: http://lkml.kernel.org/n/tip-0y9dqmmsousf69wutxwl3kkf@git.kernel.org
---
 arch/x86/kernel/setup.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 8354399..0aebd77 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -608,8 +608,6 @@ static __init void reserve_ibft_region(void)
 		memblock_reserve(addr, size);
 }
 
-static unsigned reserve_low = CONFIG_X86_RESERVE_LOW << 10;
-
 static bool __init snb_gfx_workaround_needed(void)
 {
 #ifdef CONFIG_PCI
@@ -698,8 +696,7 @@ static void __init trim_bios_range(void)
 	 * since some BIOSes are known to corrupt low memory.  See the
 	 * Kconfig help text for X86_RESERVE_LOW.
 	 */
-	e820_update_range(0, ALIGN(reserve_low, PAGE_SIZE),
-			  E820_RAM, E820_RESERVED);
+	e820_update_range(0, PAGE_SIZE, E820_RAM, E820_RESERVED);
 
 	/*
 	 * special case: Some BIOSen report the PC BIOS
@@ -711,6 +708,8 @@ static void __init trim_bios_range(void)
 	sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 }
 
+static unsigned reserve_low = CONFIG_X86_RESERVE_LOW << 10;
+
 static int __init parse_reservelow(char *p)
 {
 	unsigned long long size;
@@ -733,6 +732,11 @@ static int __init parse_reservelow(char *p)
 
 early_param("reservelow", parse_reservelow);
 
+static void __init trim_low_memory_range(void)
+{
+	memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
+}
+	
 /*
  * Determine if we were loaded by an EFI loader.  If so, then we have also been
  * passed the efi memmap, systab, etc., so we should use these data structures
@@ -987,6 +991,7 @@ void __init setup_arch(char **cmdline_p)
 	setup_real_mode();
 
 	trim_platform_memory_ranges();
+	trim_low_memory_range();
 
 	init_gbpages();
 

Re: [tip:x86/mm] x86, mm: Move reserving low memory later in initialization

[ivory]

This patch seems to make the bios_corruption_check not to cover the lowest
64kB of memory anymore but only the lowest 4kB. Was this deliberate?
When I use kernel 3.9 or higher I always get low mem corruption message from
the bios corruption checker when I resume from suspend.

Below kernel 3.9 I see this boot message:
e820 update range: 0000000000000000 - 0000000000010000 (usable) ==>
(reserved)
... which is the 64kB.

But on newer kernels the message changed to:
e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
... which is only 4kB.

The corrupted low mem areas I get the message for after resuming from
suspend is this:
 Corrupted low memory at c0002d00 (2d00 phys) = 11060000
 Corrupted low memory at c0002d04 (2d04 phys) = 80805122
 Corrupted low memory at c0002d08 (2d08 phys) = 00860003

How to fix this in kernel 3.9 and higher?

Thanks for your help and best regards.



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