On 6/17/19 5:47 AM, Borislav Petkov wrote:
> 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?
Yes and no... it doesn't say how it is done, namely through the use of
memblock_reserve() calls and when and where those occur.
>
>> 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 <b...@redhat.com>
>> Cc: Lianbo Jiang <liji...@redhat.com>
>> Signed-off-by: Tom Lendacky <thomas.lenda...@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* ...
The comment above is more explicit about what will be discarded and
how not to have it discarded, so I removed this comment.
Thanks,
Tom
>
>> DISCARDS
>> /DISCARD/ : {
>> *(.eh_frame)
>
