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Subject[PATCH v3 1/2] x86/mm: Identify the end of the kernel area to be reserved
Date
The memory occupied by the kernel is reserved using memblock_reserve()
in setup_arch(). Currently, the area is from symbols _text to __bss_stop.
Everything after __bss_stop must be specifically reserved otherwise it
is discarded. This is not clearly documented.

Add a new symbol, __end_of_kernel_reserve, that more readily identifies
what is reserved, along with comments that indicate what is reserved,
what is discarded and what needs to be done to prevent a section from
being discarded.

Tested-by: Lianbo Jiang <lijiang@redhat.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
arch/x86/include/asm/sections.h | 2 ++
arch/x86/kernel/setup.c | 8 +++++++-
arch/x86/kernel/vmlinux.lds.S | 9 ++++++++-
3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index 8ea1cfdbeabc..71b32f2570ab 100644
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -13,4 +13,6 @@ extern char __end_rodata_aligned[];
extern char __end_rodata_hpage_align[];
#endif

+extern char __end_of_kernel_reserve[];
+
#endif /* _ASM_X86_SECTIONS_H */
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 08a5f4a131f5..fe0f6ebefeb7 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -827,8 +827,14 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)

void __init setup_arch(char **cmdline_p)
{
+ /*
+ * Reserve the memory occupied by the kernel between _text and
+ * __end_of_kernel_reserve symbols. Any kernel sections after the
+ * __end_of_kernel_reserve symbol must be explicity reserved with a
+ * separate memblock_reserve() or they will be discarded.
+ */
memblock_reserve(__pa_symbol(_text),
- (unsigned long)__bss_stop - (unsigned long)_text);
+ (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);

/*
* Make sure page 0 is always reserved because on systems with
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 0850b5149345..ca2252ca6ad7 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -368,6 +368,14 @@ SECTIONS
__bss_stop = .;
}

+ /*
+ * The memory occupied from _text to here, __end_of_kernel_reserve, is
+ * automatically reserved in setup_arch(). Anything after here must be
+ * explicitly reserved using memblock_reserve() or it will be discarded
+ * and treated as available memory.
+ */
+ __end_of_kernel_reserve = .;
+
. = ALIGN(PAGE_SIZE);
.brk : AT(ADDR(.brk) - LOAD_OFFSET) {
__brk_base = .;
@@ -382,7 +390,6 @@ SECTIONS
STABS_DEBUG
DWARF_DEBUG

- /* Sections to be discarded */
DISCARDS
/DISCARD/ : {
*(.eh_frame)
--
2.17.1
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