A given page of memory can only be accepted once. The kernel has to
accept memory both in the early decompression stage and during normal
runtime.
A bitmap is used to communicate the acceptance state of each page
between the decompression stage and normal runtime.
boot_params is used to communicate location of the bitmap throughout
the boot. The bitmap is allocated and initially populated in EFI stub.
Decompression stage accepts pages required for kernel/initrd and marks
these pages accordingly in the bitmap. The main kernel picks up the
bitmap from the same boot_params and uses it to determine what has to
be accepted on allocation.
In the runtime kernel, reserve the bitmap's memory to ensure nothing
overwrites it.
The size of bitmap is determined with e820__end_of_ram_pfn() which
relies on setup_e820() marking unaccepted memory as E820_TYPE_RAM.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
---
arch/x86/kernel/e820.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 9dac24680ff8..62068956bb76 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -1316,6 +1316,23 @@ void __init e820__memblock_setup(void)
int i;
u64 end;
+ /*
+ * Mark unaccepted memory bitmap reserved.
+ *
+ * This kind of reservation usually done from early_reserve_memory(),
+ * but early_reserve_memory() called before e820__memory_setup(), so
+ * e820_table is not finalized and e820__end_of_ram_pfn() cannot be
+ * used to get correct RAM size.
+ */
+ 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
--
2.38.0
