On Fri, Jun 24, 2016 at 04:12:02PM +0200, Ard Biesheuvel wrote:
> 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.
>
Indeed. So let's go back to the method below...
>
> >>
> >> 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.
>
At least for me, this approach will mitigate the inconsistence in some degree while
keeping the similar logic as it was, so I will post an updated version patch soon.
Thanks,
Dennis
>
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