On 24 June 2016 at 14:01, Dennis Chen <dennis.chen@xxxxxxx> wrote:
> On Fri, Jun 24, 2016 at 12:43:52PM +0200, Ard Biesheuvel wrote:
>> On 24 June 2016 at 05:13, Dennis Chen <dennis.chen@xxxxxxx> wrote:
>> > When booting an ACPI enabled kernel with 'mem=', probably the ACPI data
>> > regions loaded by firmware will beyond the limit of the memory, in this
>> > case we need to nomap the region above the limit while not removing
>> > it from memblock, because once region removed from memblock, the ACPI
>> > will think that region is not a normal memory and map it as device type
>> > memory accordingly. Since the ACPI core will produce non-alignment access
>> > when paring AML data stream, hence result in alignment fault upon the io
>> > mapped memory space.
>> >
>> > For example, below is an alignment exception observed on softIron board
>> > when booting the kernel with 'acpi=force mem=8G':
>> > ...
>> > [ 0.542475] Unable to handle kernel paging request at virtual address ffff0000080521e7
>> > [ 0.550457] pgd = ffff000008aa0000
>> > [ 0.553880] [ffff0000080521e7] *pgd=000000801fffe003, *pud=000000801fffd003, *pmd=000000801fffc003, *pte=00e80083ff1c1707
>> > [ 0.564939] Internal error: Oops: 96000021 [#1] PREEMPT SMP
>> > [ 0.570553] Modules linked in:
>> > [ 0.573626] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.7.0-rc3-next-20160616+ #172
>> > [ 0.581344] Hardware name: AMD Overdrive/Supercharger/Default string, BIOS ROD1001A 02/09/2016
>> > [ 0.590025] task: ffff800001ef0000 ti: ffff800001ef8000 task.ti: ffff800001ef8000
>> > [ 0.597571] PC is at acpi_ns_lookup+0x520/0x734
>> > [ 0.602134] LR is at acpi_ns_lookup+0x4a4/0x734
>> > [ 0.606693] pc : [<ffff0000083b8b10>] lr : [<ffff0000083b8a94>] pstate: 60000045
>> > [ 0.614145] sp : ffff800001efb8b0
>> > [ 0.617478] x29: ffff800001efb8c0 x28: 000000000000001b
>> > [ 0.622829] x27: 0000000000000001 x26: 0000000000000000
>> > [ 0.628181] x25: ffff800001efb9e8 x24: ffff000008a10000
>> > [ 0.633531] x23: 0000000000000001 x22: 0000000000000001
>> > [ 0.638881] x21: ffff000008724000 x20: 000000000000001b
>> > [ 0.644230] x19: ffff0000080521e7 x18: 000000000000000d
>> > [ 0.649580] x17: 00000000000038ff x16: 0000000000000002
>> > [ 0.654929] x15: 0000000000000007 x14: 0000000000007fff
>> > [ 0.660278] x13: ffffff0000000000 x12: 0000000000000018
>> > [ 0.665627] x11: 000000001fffd200 x10: 00000000ffffff76
>> > [ 0.670978] x9 : 000000000000005f x8 : ffff000008725fa8
>> > [ 0.676328] x7 : ffff000008a8df70 x6 : ffff000008a8df70
>> > [ 0.681679] x5 : ffff000008a8d000 x4 : 0000000000000010
>> > [ 0.687027] x3 : 0000000000000010 x2 : 000000000000000c
>> > [ 0.692378] x1 : 0000000000000006 x0 : 0000000000000000
>> > ...
>> > [ 1.262235] [<ffff0000083b8b10>] acpi_ns_lookup+0x520/0x734
>> > [ 1.267845] [<ffff0000083a7160>] acpi_ds_load1_begin_op+0x174/0x4fc
>> > [ 1.274156] [<ffff0000083c1f4c>] acpi_ps_build_named_op+0xf8/0x220
>> > [ 1.280380] [<ffff0000083c227c>] acpi_ps_create_op+0x208/0x33c
>> > [ 1.286254] [<ffff0000083c1820>] acpi_ps_parse_loop+0x204/0x838
>> > [ 1.292215] [<ffff0000083c2fd4>] acpi_ps_parse_aml+0x1bc/0x42c
>> > [ 1.298090] [<ffff0000083bc6e8>] acpi_ns_one_complete_parse+0x1e8/0x22c
>> > [ 1.304753] [<ffff0000083bc7b8>] acpi_ns_parse_table+0x8c/0x128
>> > [ 1.310716] [<ffff0000083bb8fc>] acpi_ns_load_table+0xc0/0x1e8
>> > [ 1.316591] [<ffff0000083c9068>] acpi_tb_load_namespace+0xf8/0x2e8
>> > [ 1.322818] [<ffff000008984128>] acpi_load_tables+0x7c/0x110
>> > [ 1.328516] [<ffff000008982ea4>] acpi_init+0x90/0x2c0
>> > [ 1.333603] [<ffff0000080819fc>] do_one_initcall+0x38/0x12c
>> > [ 1.339215] [<ffff000008960cd4>] kernel_init_freeable+0x148/0x1ec
>> > [ 1.345353] [<ffff0000086b7d30>] kernel_init+0x10/0xec
>> > [ 1.350529] [<ffff000008084e10>] ret_from_fork+0x10/0x40
>> > [ 1.355878] Code: b9009fbc 2a00037b 36380057 3219037b (b9400260)
>> > [ 1.362035] ---[ end trace 03381e5eb0a24de4 ]---
>> > [ 1.366691] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>> >
>> > With 'efi=debug', we can see those ACPI regions loaded by firmware on
>> > that board as:
>> > [ 0.000000] efi: 0x0083ff1b5000-0x0083ff1c2fff [ACPI Reclaim Memory| | | | | | | | |WB|WT|WC|UC]*
>> > [ 0.000000] efi: 0x0083ff223000-0x0083ff224fff [ACPI Memory NVS | | | | | | | | |WB|WT|WC|UC]*
>> >
>> > This patch is trying to address the above issues by nomaping the region
>> > instead of removing it.
>> >
>> > Signed-off-by: Dennis Chen <dennis.chen@xxxxxxx>
>> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
>> > Cc: Steve Capper <steve.capper@xxxxxxx>
>> > Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>> > Cc: Will Deacon <will.deacon@xxxxxxx>
>> > Cc: Mark Rutland <mark.rutland@xxxxxxx>
>> > Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>> > Cc: Matt Fleming <matt@xxxxxxxxxxxxxxxxxxx>
>> > Cc: linux-mm@xxxxxxxxx
>> > Cc: linux-acpi@xxxxxxxxxxxxxxx
>> > Cc: linux-efi@xxxxxxxxxxxxxxx
>> > ---
>> > Changes in v2:
>> > Update the commit message and remove the memblock_is_map_memory() check
>> > according to the suggestion from Mark Rutland.
>> >
>> > arch/arm64/mm/init.c | 9 +++++----
>> > 1 file changed, 5 insertions(+), 4 deletions(-)
>> >
>> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> > index d45f862..6af2456 100644
>> > --- a/arch/arm64/mm/init.c
>> > +++ b/arch/arm64/mm/init.c
>> > @@ -222,12 +222,13 @@ void __init arm64_memblock_init(void)
>> >
>> > /*
>> > * Apply the memory limit if it was set. Since the kernel may be loaded
>> > - * high up in memory, add back the kernel region that must be accessible
>> > - * via the linear mapping.
>> > + * in the memory regions above the limit, so we need to clear the
>> > + * MEMBLOCK_NOMAP flag of this region to make it can be accessible via
>> > + * the linear mapping.
>> > */
>> > if (memory_limit != (phys_addr_t)ULLONG_MAX) {
>> > - memblock_enforce_memory_limit(memory_limit);
>> > - memblock_add(__pa(_text), (u64)(_end - _text));
>> > + memblock_mem_limit_mark_nomap(memory_limit);
>> > + memblock_clear_nomap(__pa(_text), (u64)(_end - _text));
>>
>> Up until now, we have ignored the effect of having NOMAP memblocks on
>> the return values of functions like memblock_phys_mem_size() and
>> memblock_mem_size(), since they could reasonably be expected to cover
>> only a small slice of all available memory. However, after applying
>> this patch, it may well be the case that most of memory is marked
>> NOMAP, and these functions will cease to work as expected.
>>
> Hi Ard, I noticed these inconsistences as you mentioned, but seems the
> available memory is limited correctly. For this case('mem='), will it bring
> some substantive side effects except that some log messages maybe confusing?
That is exactly the question that needs answering before we can merge
these patches. I know we consider mem= a development hack, but the
intent is to make it appear to the kernel as if only a smaller amount
of memory is available to the kernel, and this is signficantly
different from having memblock_mem_size() et al return much larger
values than what is actually available. Perhaps this doesn't matter at
all, but it is something we must discuss before proceeding with these
changes.
>>
>> This means NOMAP is really only suited to punch some holes into the
>> kernel direct mapping, and so implementing the memory limit by marking
>> everything NOMAP is not the way to go. Instead, we should probably
>> reorder the init sequence so that the regions that are reserved in the
>> UEFI memory map are declared and marked NOMAP [again] after applying
>> the memory limit in the old way.
>>
> Before this patch, I have another one addressing the same issue [1], with
> that patch we'll not have these inconsistences, but it looks like a little
> bit complicated, so it becomes current one. Any comments about that?
>
> [1]http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/438443.html
>
The problem caused by mem= is that it removes regions that are marked
NOMAP. So instead of marking everything above the limit NOMAP, I would
much rather see an alternative implementation of
memblock_enforce_memory_limit() that enforces the mem= limit by only
removing memblocks that have to NOMAP flag cleared, and leaving the
NOMAP ones where they are.
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