x86, bios: Make the x86 early memory reservation a kernel option

Add a kernel command-line option so the x86 early memory reservation
size can be adjusted at runtime instead of only at compile time.

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <tip-d0cd7425fab774a480cce17c2f649984312d0b55@git.kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

3 files changed, 32 insertions, 3 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 2c85c0692b01..41ce93e71ded 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2150,6 +2150,11 @@ and is between 256 and 4096 characters. It is defined in the file
                         Reserves a hole at the top of the kernel virtual
                         address space.
 
+        reservelow=     [X86]
+                        Format: nn[K]
+                        Set the amount of memory to reserve for BIOS at
+                        the bottom of the address space.
+
         reset_devices   [KNL] Force drivers to reset the underlying device
                         during initialization.
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 683ae8f9bd0b..d3590008c5dc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1326,7 +1326,7 @@ config X86_BOOTPARAM_MEMORY_CORRUPTION_CHECK
           Set whether the default state of memory_corruption_check is
           on or off.
 
-config X86_LOW_RESERVE
+config X86_RESERVE_LOW
         int "Amount of low memory, in kilobytes, to reserve for the BIOS"
         default 64
         range 4 640
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index eb87f1c83f91..af277e369def 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -618,6 +618,8 @@ static __init void reserve_ibft_region(void)
                 reserve_early_overlap_ok(addr, addr + size, "ibft");
 }
 
+static unsigned reserve_low = CONFIG_X86_RESERVE_LOW << 10;
+
 static void __init trim_bios_range(void)
 {
         /*
@@ -627,9 +629,9 @@ static void __init trim_bios_range(void)
          *
          * This typically reserves additional memory (64KiB by default)
          * since some BIOSes are known to corrupt low memory.  See the
-         * Kconfig help text for X86_LOW_RESERVE.
+         * Kconfig help text for X86_RESERVE_LOW.
          */
-        e820_update_range(0, ALIGN(CONFIG_X86_LOW_RESERVE << 10, PAGE_SIZE),
+        e820_update_range(0, ALIGN(reserve_low, PAGE_SIZE),
                           E820_RAM, E820_RESERVED);
 
         /*
@@ -641,6 +643,28 @@ static void __init trim_bios_range(void)
         sanitize_e820_map(e820.map, ARRAY_SIZE(e820.map), &e820.nr_map);
 }
 
+static int __init parse_reservelow(char *p)
+{
+        unsigned long long size;
+
+        if (!p)
+                return -EINVAL;
+
+        size = memparse(p, &p);
+
+        if (size < 4096)
+                size = 4096;
+
+        if (size > 640*1024)
+                size = 640*1024;
+
+        reserve_low = size;
+
+        return 0;
+}
+
+early_param("reservelow", parse_reservelow);
+
 /*
  * 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