[PATCHv3 5/7] x86/mm: Reserve unaccepted memory bitmap

[Kirill A. Shutemov]

A given page of memory can only be accepted once.  The kernel has a need
to accept memory both in the early decompression stage and during normal
runtime.

Use a bitmap to communicate the acceptance state of each page between
the decompression stage and normal runtime.  This eliminates the
possibility of attempting to double-accept a page.

Allocate the bitmap during decompression stage and hand it over to the
main kernel image via boot_params.

In the runtime kernel, reserve the bitmap's memory to ensure nothing
overwrites it.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/e820.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index bc0657f0deed..3905bd1ca41d 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1297,6 +1297,16 @@ void __init e820__memblock_setup(void)
 	int i;
 	u64 end;
 
+	/* Mark unaccepted memory bitmap reserved */
+	if (boot_params.unaccepted_memory) {
+		unsigned long size;
+
+		/* One bit per 2MB */
+		size = DIV_ROUND_UP(e820__end_of_ram_pfn() * PAGE_SIZE,
+				    PMD_SIZE * BITS_PER_BYTE);
+		memblock_reserve(boot_params.unaccepted_memory, size);
+	}
+
 	/*
 	 * The bootstrap memblock region count maximum is 128 entries
 	 * (INIT_MEMBLOCK_REGIONS), but EFI might pass us more E820 entries
-- 
2.34.1