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@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Tested-by: Lianbo Jiang <lijiang@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <rrichter@marvell.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Sinan Kaya <okaya@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "x86@kernel.org" <x86@kernel.org>
Link: https://lkml.kernel.org/r/7db7da45b435f8477f25e66f292631ff766a844c.1560969363.git.thomas.lendacky@amd.com

diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index 8ea1cfd..71b32f2 100644 (file)
--- 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 08a5f4a..dac60ad 100644 (file)
--- 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 0850b51..ca2252c 100644 (file)
--- 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)