Subject: [PATCH 1/2] mm: memblock Add some new functions to address the mem limit issue

From: [email-masked] (Dennis Chen)
Date: Fri, 24 Jun 2016 10:28:28 +0800

On Thu, Jun 23, 2016 at 01:57:48PM +0100, Mark Rutland wrote:
> On Thu, Jun 23, 2016 at 07:30:14PM +0800, Dennis Chen wrote:
> > Two major changes in this patch:
> > [1] Add memblock_mem_limit_mark_nomap(phys_addr_t limit) function to
> > mark memblock regions above the @limit as NOMAP region, which will
> > be used to address the observed 'mem=x' kernel parameter issue.
> > 
> > [2] Add 'size' and 'flag' debug output in the memblock debugfs.
> > The '/sys/kernel/debug/memblock/memory' output looks like before:
> >    0: 0x0000008000000000..0x0000008001e7ffff
> >    1: 0x0000008001e80000..0x00000083ff184fff
> >    2: 0x00000083ff185000..0x00000083ff1c2fff
> >    3: 0x00000083ff1c3000..0x00000083ff222fff
> >    4: 0x00000083ff223000..0x00000083ffe42fff
> >    5: 0x00000083ffe43000..0x00000083ffffffff
> > 
> > With this patch applied:
> >    0: 0x0000008000000000..0x0000008001e7ffff  0x0000000001e80000  0x4
> >    1: 0x0000008001e80000..0x00000083ff184fff  0x00000003fd305000  0x0
> >    2: 0x00000083ff185000..0x00000083ff1c2fff  0x000000000003e000  0x4
> >    3: 0x00000083ff1c3000..0x00000083ff222fff  0x0000000000060000  0x0
> >    4: 0x00000083ff223000..0x00000083ffe42fff  0x0000000000c20000  0x4
> >    5: 0x00000083ffe43000..0x00000083ffffffff  0x00000000001bd000  0x0
> 
> Please explain in the commit message what the problem being solved is,
> and how this solves it. e.g.
> 
> In some cases, memblock is queried to determine whether a physical
> address corresponds to memory present in a system even if unused by the
> OS for the linear mapping, highmem, etc. For example, the ACPI core
> needs this information to determine which attributes to use when mapping
> ACPI regions. Use of incorrect memory types can result in faults, data
> corruption, or other issues.
> 
> Removing memory with memblock_enforce_memory_limit throws away this
> information, and so a kernel booted with mem= may suffer from the issues
> described above. To avoid this, we can mark regions as nomap rather than
> removing them, which preserves the information we need while preventing
> other use of the regions.
> 
> This patch adds new insfrastructure to mark all memblock regions in an
> address range as nomap, to cater for this. Similarly we add
> infrastructure to clear the flag for an address range, which makes
> handling some overlap cases simpler.
> 
> Other than that, the patch itself looks fine to me.
>
The above commit message is very clear to describe why we need to add
those new infrastructures in this patch. Thanks Mark, you're saving 
my time :) I will apply it in the next version.

Thanks,
Dennis
> 
> Thanks,
> Mark.
> 
> > Signed-off-by: Dennis Chen <[email-masked]>
> > Cc: Catalin Marinas <[email-masked]>
> > Cc: Steve Capper <[email-masked]>
> > Cc: Ard Biesheuvel <[email-masked]>
> > Cc: Will Deacon <[email-masked]>
> > Cc: Mark Rutland <[email-masked]>
> > Cc: Rafael J. Wysocki <[email-masked]>
> > Cc: Matt Fleming <[email-masked]>
> > Cc: linux-mm at kvack.org
> > Cc: linux-acpi at vger.kernel.org
> > Cc: linux-efi at vger.kernel.org
> > ---
> >  include/linux/memblock.h |  2 ++
> >  mm/memblock.c            | 50 ++++++++++++++++++++++++++++++++++++++++--------
> >  2 files changed, 44 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index 6c14b61..5e069c8 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -92,6 +92,7 @@ int memblock_mark_hotplug(phys_addr_t base, phys_addr_t size);
> >  int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
> >  int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
> >  int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
> > +int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
> >  ulong choose_memblock_flags(void);
> >  
> >  /* Low level functions */
> > @@ -332,6 +333,7 @@ phys_addr_t memblock_mem_size(unsigned long limit_pfn);
> >  phys_addr_t memblock_start_of_DRAM(void);
> >  phys_addr_t memblock_end_of_DRAM(void);
> >  void memblock_enforce_memory_limit(phys_addr_t memory_limit);
> > +void memblock_mem_limit_mark_nomap(phys_addr_t limit);
> >  bool memblock_is_memory(phys_addr_t addr);
> >  int memblock_is_map_memory(phys_addr_t addr);
> >  int memblock_is_region_memory(phys_addr_t base, phys_addr_t size);
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index ca09915..60930ac 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -814,6 +814,18 @@ int __init_memblock memblock_mark_nomap(phys_addr_t base, phys_addr_t size)
> >  }
> >  
> >  /**
> > + * memblock_clear_nomap - Clear flag MEMBLOCK_NOMAP for a specified region.
> > + * @base: the base phys addr of the region
> > + * @size: the size of the region
> > + *
> > + * Return 0 on success, -errno on failure.
> > + */
> > +int __init_memblock memblock_clear_nomap(phys_addr_t base, phys_addr_t size)
> > +{
> > +	return memblock_setclr_flag(base, size, 0, MEMBLOCK_NOMAP);
> > +}
> > +
> > +/**
> >   * __next_reserved_mem_region - next function for for_each_reserved_region()
> >   * @idx: pointer to u64 loop variable
> >   * @out_start: ptr to phys_addr_t for start address of the region, can be %NULL
> > @@ -1465,14 +1477,11 @@ phys_addr_t __init_memblock memblock_end_of_DRAM(void)
> >  	return (memblock.memory.regions[idx].base + memblock.memory.regions[idx].size);
> >  }
> >  
> > -void __init memblock_enforce_memory_limit(phys_addr_t limit)
> > +static phys_addr_t __find_max_addr(phys_addr_t limit)
> >  {
> >  	phys_addr_t max_addr = (phys_addr_t)ULLONG_MAX;
> >  	struct memblock_region *r;
> >  
> > -	if (!limit)
> > -		return;
> > -
> >  	/* find out max address */
> >  	for_each_memblock(memory, r) {
> >  		if (limit <= r->size) {
> > @@ -1482,6 +1491,18 @@ void __init memblock_enforce_memory_limit(phys_addr_t limit)
> >  		limit -= r->size;
> >  	}
> >  
> > +	return max_addr;
> > +}
> > +
> > +void __init memblock_enforce_memory_limit(phys_addr_t limit)
> > +{
> > +	phys_addr_t max_addr;
> > +
> > +	if (!limit)
> > +		return;
> > +
> > +	max_addr = __find_max_addr(limit);
> > +
> >  	/* truncate both memory and reserved regions */
> >  	memblock_remove_range(&memblock.memory, max_addr,
> >  			      (phys_addr_t)ULLONG_MAX);
> > @@ -1489,6 +1510,17 @@ void __init memblock_enforce_memory_limit(phys_addr_t limit)
> >  			      (phys_addr_t)ULLONG_MAX);
> >  }
> >  
> > +void __init memblock_mem_limit_mark_nomap(phys_addr_t limit)
> > +{
> > +	phys_addr_t max_addr;
> > +
> > +	if (!limit)
> > +		return;
> > +
> > +	max_addr = __find_max_addr(limit);
> > +	memblock_mark_nomap(max_addr, (phys_addr_t)ULLONG_MAX);
> > +}
> > +
> >  static int __init_memblock memblock_search(struct memblock_type *type, phys_addr_t addr)
> >  {
> >  	unsigned int left = 0, right = type->cnt;
> > @@ -1677,13 +1709,15 @@ static int memblock_debug_show(struct seq_file *m, void *private)
> >  		reg = &type->regions[i];
> >  		seq_printf(m, "%4d: ", i);
> >  		if (sizeof(phys_addr_t) == 4)
> > -			seq_printf(m, "0x%08lx..0x%08lx\n",
> > +			seq_printf(m, "0x%08lx..0x%08lx  0x%08lx  0x%lx\n",
> >  				   (unsigned long)reg->base,
> > -				   (unsigned long)(reg->base + reg->size - 1));
> > +				   (unsigned long)(reg->base + reg->size - 1),
> > +				   (unsigned long)reg->size, reg->flags);
> >  		else
> > -			seq_printf(m, "0x%016llx..0x%016llx\n",
> > +			seq_printf(m, "0x%016llx..0x%016llx  0x%016llx  0x%lx\n",
> >  				   (unsigned long long)reg->base,
> > -				   (unsigned long long)(reg->base + reg->size - 1));
> > +				   (unsigned long long)(reg->base + reg->size - 1),
> > +				   (unsigned long long)reg->size, reg->flags);
> >  
> >  	}
> >  	return 0;
> > -- 
> > 1.8.3.1
> > 
>