[PATCH] x86/boot/e820: add new chareater "-" to free BIOS memory in memmap bootargs

[zoucao@linux.alibaba.com]

From: zoucao <zoucao@localhost.localdomain>

Normally every BIOS reserved memory is used for some features, we can't
use them, but in some conditions,  users can ensure some BIOS memories
are not used and reserved memory is well to free, they have not a good
way to free these memories, here add a new chareater "-" in memmap to
free reserved memory.

Signed-off-by: zou cao <zoucao@linux.alibaba.com>
---
 7u/Documentation/kernel-parameters.txt | 6 ++++++
 7u/arch/x86/kernel/e820.c              | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/7u/Documentation/kernel-parameters.txt b/7u/Documentation/kernel-parameters.txt
index 9a1abb99a..dbea75e12 100644
--- a/7u/Documentation/kernel-parameters.txt
+++ b/7u/Documentation/kernel-parameters.txt
@@ -1677,6 +1677,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			         or
 			         memmap=0x10000$0x18690000
 
+	memmap=nn[KMG]-ss[KMG]
+			Free E820 reserved memory, as specified by the user.
+			Region of reserved memory to be free, from ss to ss+nn.
+			Example: free reserved memory from 0x18690000-0x186a0000
+					memmap=0x4101000-0x6aeff000
+
 	memory_corruption_check=0/1 [X86]
 			Some BIOSes seem to corrupt the first 64k of
 			memory when doing things like suspend/resume.
diff --git a/7u/arch/x86/kernel/e820.c b/7u/arch/x86/kernel/e820.c
index 174da5fc5..b8a042981 100644
--- a/7u/arch/x86/kernel/e820.c
+++ b/7u/arch/x86/kernel/e820.c
@@ -875,6 +875,9 @@ static int __init parse_memmap_one(char *p)
 	} else if (*p == '$') {
 		start_at = memparse(p+1, &p);
 		e820_add_region(start_at, mem_size, E820_RESERVED);
+	} else if (*p == '-') {
+		start_at = memparse(p+1, &p);
+		e820_remove_range(start_at, mem_size, E820_RESERVED, E820_RAM);
 	} else
 		e820_remove_range(mem_size, ULLONG_MAX - mem_size, E820_RAM, 1);
 
-- 
2.14.1.40.g8e62ba1