Re: [PATCH v2 01/12] mm/memblock: add MEMBLOCK_NOMAP attribute to memblock memory table

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 16 November 2015 at 19:58, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> On Mon, Nov 16, 2015 at 07:32:26PM +0100, Ard Biesheuvel wrote:
>> This introduces the MEMBLOCK_NOMAP attribute and the required plumbing
>> to make it usable as an indicator that some parts of normal memory
>> should not be covered by the kernel direct mapping. It is up to the
>> arch to actually honor the attribute when laying out this mapping,
>> but the memblock code itself is modified to disregard these regions
>> for allocations and other general use.
>
> What does NOMAP mean for the rest of the kernel?  Does this mean the
> memory is never handed over to the kernel page allocators for kernel
> use - in a similar way to what we do with arm_memblock_steal() ?
>

The main difference is that memblock_is_memory() still returns true
for the region. This is useful in some cases, e.g., to decide which
attributes to use when mapping.

>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> ---
>>  include/linux/memblock.h |  8 ++++++
>>  mm/memblock.c            | 28 ++++++++++++++++++++
>>  2 files changed, 36 insertions(+)
>>
>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>> index 24daf8fc4d7c..fec66f86eeff 100644
>> --- a/include/linux/memblock.h
>> +++ b/include/linux/memblock.h
>> @@ -25,6 +25,7 @@ enum {
>>       MEMBLOCK_NONE           = 0x0,  /* No special request */
>>       MEMBLOCK_HOTPLUG        = 0x1,  /* hotpluggable region */
>>       MEMBLOCK_MIRROR         = 0x2,  /* mirrored region */
>> +     MEMBLOCK_NOMAP          = 0x4,  /* don't add to kernel direct mapping */
>>  };
>>
>>  struct memblock_region {
>> @@ -82,6 +83,7 @@ bool memblock_overlaps_region(struct memblock_type *type,
>>  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);
>>  ulong choose_memblock_flags(void);
>>
>>  /* Low level functions */
>> @@ -184,6 +186,11 @@ static inline bool memblock_is_mirror(struct memblock_region *m)
>>       return m->flags & MEMBLOCK_MIRROR;
>>  }
>>
>> +static inline bool memblock_is_nomap(struct memblock_region *m)
>> +{
>> +     return m->flags & MEMBLOCK_NOMAP;
>> +}
>> +
>>  #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
>>  int memblock_search_pfn_nid(unsigned long pfn, unsigned long *start_pfn,
>>                           unsigned long  *end_pfn);
>> @@ -319,6 +326,7 @@ 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);
>>  int 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);
>>  int memblock_is_reserved(phys_addr_t addr);
>>  bool memblock_is_region_reserved(phys_addr_t base, phys_addr_t size);
>> diff --git a/mm/memblock.c b/mm/memblock.c
>> index d300f1329814..07ff069fef25 100644
>> --- a/mm/memblock.c
>> +++ b/mm/memblock.c
>> @@ -822,6 +822,17 @@ int __init_memblock memblock_mark_mirror(phys_addr_t base, phys_addr_t size)
>>       return memblock_setclr_flag(base, size, 1, MEMBLOCK_MIRROR);
>>  }
>>
>> +/**
>> + * memblock_mark_nomap - Mark a memory region with flag MEMBLOCK_NOMAP.
>> + * @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_mark_nomap(phys_addr_t base, phys_addr_t size)
>> +{
>> +     return memblock_setclr_flag(base, size, 1, MEMBLOCK_NOMAP);
>> +}
>>
>>  /**
>>   * __next_reserved_mem_region - next function for for_each_reserved_region()
>> @@ -913,6 +924,10 @@ void __init_memblock __next_mem_range(u64 *idx, int nid, ulong flags,
>>               if ((flags & MEMBLOCK_MIRROR) && !memblock_is_mirror(m))
>>                       continue;
>>
>> +             /* skip nomap memory unless we were asked for it explicitly */
>> +             if (!(flags & MEMBLOCK_NOMAP) && memblock_is_nomap(m))
>> +                     continue;
>> +
>>               if (!type_b) {
>>                       if (out_start)
>>                               *out_start = m_start;
>> @@ -1022,6 +1037,10 @@ void __init_memblock __next_mem_range_rev(u64 *idx, int nid, ulong flags,
>>               if ((flags & MEMBLOCK_MIRROR) && !memblock_is_mirror(m))
>>                       continue;
>>
>> +             /* skip nomap memory unless we were asked for it explicitly */
>> +             if (!(flags & MEMBLOCK_NOMAP) && memblock_is_nomap(m))
>> +                     continue;
>> +
>>               if (!type_b) {
>>                       if (out_start)
>>                               *out_start = m_start;
>> @@ -1519,6 +1538,15 @@ int __init_memblock memblock_is_memory(phys_addr_t addr)
>>       return memblock_search(&memblock.memory, addr) != -1;
>>  }
>>
>> +int __init_memblock memblock_is_map_memory(phys_addr_t addr)
>> +{
>> +     int i = memblock_search(&memblock.memory, addr);
>> +
>> +     if (i == -1)
>> +             return false;
>> +     return !memblock_is_nomap(&memblock.memory.regions[i]);
>> +}
>> +
>>  #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
>>  int __init_memblock memblock_search_pfn_nid(unsigned long pfn,
>>                        unsigned long *start_pfn, unsigned long *end_pfn)
>> --
>> 1.9.1
>>
>
> --
> FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
> according to speedtest.net.

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