Messages in this thread Patch in this message | | | Date | Mon, 17 Jun 2019 12:47:40 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v2 1/2] x86/mm: Identify the end of the kernel area to be reserved |
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On Fri, Jun 14, 2019 at 09:15:18PM +0000, Lendacky, Thomas wrote: > 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.
Hmm, so I see this in arch/x86/kernel/vmlinux.lds.S after _end:
_end = .;
STABS_DEBUG DWARF_DEBUG
/* Sections to be discarded */ DISCARDS /DISCARD/ : { *(.eh_frame) }
and over DISCARDS:
/* * Default discarded sections. * * Some archs want to discard exit text/data at runtime rather than * link time due to cross-section references such as alt instructions, * bug table, eh_frame, etc. DISCARDS must be the last of output * section definitions so that such archs put those in earlier section * definitions. */ #define DISCARDS
That sounds like it is documented to me, or do you mean something else?
> 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. > > Cc: Baoquan He <bhe@redhat.com> > Cc: Lianbo Jiang <lijiang@redhat.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..32eb70625b3b 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 it will be discarded.
s/it/they/
> + */ > 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 */
Huh?
They're called DISCARD* ...
> DISCARDS > /DISCARD/ : { > *(.eh_frame)
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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