linux-kernel - [tip:x86/kdump] x86/mm: Identify the end of the kernel area to be reserved

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Message-ID: <tip-c603a309cc75f3dd018ddb20ee44c05047918cbf@git.kernel.org>
Date:   Thu, 20 Jun 2019 02:58:16 -0700
From:   tip-bot for Thomas Lendacky <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     dave.hansen@...el.com, keescook@...omium.org,
        ndesaulniers@...gle.com, luto@...nel.org, samitolvanen@...gle.com,
        mingo@...hat.com, dyoung@...hat.com, x86@...nel.org,
        Thomas.Lendacky@....com, hpa@...or.com, brijesh.singh@....com,
        okaya@...eaurora.org, jgross@...e.com,
        linux-kernel@...r.kernel.org, mingo@...nel.org, lijiang@...hat.com,
        rrichter@...vell.com, pasha.tatashin@...cle.com,
        peterz@...radead.org, bp@...e.de, jroedel@...e.de, bhe@...hat.com,
        tglx@...utronix.de, thomas.lendacky@....com
Subject: [tip:x86/kdump] x86/mm: Identify the end of the kernel area to be
 reserved

Commit-ID:  c603a309cc75f3dd018ddb20ee44c05047918cbf
Gitweb:     https://git.kernel.org/tip/c603a309cc75f3dd018ddb20ee44c05047918cbf
Author:     Thomas Lendacky <Thomas.Lendacky@....com>
AuthorDate: Wed, 19 Jun 2019 18:40:57 +0000
Committer:  Borislav Petkov <bp@...e.de>
CommitDate: Thu, 20 Jun 2019 09:22:47 +0200

x86/mm: Identify the end of the kernel area to be reserved

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.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Baoquan He <bhe@...hat.com>
Reviewed-by: Dave Hansen <dave.hansen@...el.com>
Tested-by: Lianbo Jiang <lijiang@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Brijesh Singh <brijesh.singh@....com>
Cc: Dave Young <dyoung@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Joerg Roedel <jroedel@...e.de>
Cc: Juergen Gross <jgross@...e.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Pavel Tatashin <pasha.tatashin@...cle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Robert Richter <rrichter@...vell.com>
Cc: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Sinan Kaya <okaya@...eaurora.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: "x86@...nel.org" <x86@...nel.org>
Link: https://lkml.kernel.org/r/7db7da45b435f8477f25e66f292631ff766a844c.1560969363.git.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..dac60ad37e5e 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 explicitly 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)