Re: [RFC PATCH 1/4] libnvdimm/namespace: Make namespace size validation arch dependent

[Dan Williams <dan.j.williams@intel.com>]

On Mon, Oct 28, 2019 at 2:48 AM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> The page size used to map the namespace is arch dependent. For example
> architectures like ppc64 use 16MB page size for direct-mapping. If the namespace
> size is not aligned to the mapping page size, we can observe kernel crash
> during namespace init and destroy.
>
> This is due to kernel doing partial map/unmap of the resource range
>
> BUG: Unable to handle kernel data access at 0xc001000406000000
> Faulting instruction address: 0xc000000000090790
> NIP [c000000000090790] arch_add_memory+0xc0/0x130
> LR [c000000000090744] arch_add_memory+0x74/0x130
> Call Trace:
>  arch_add_memory+0x74/0x130 (unreliable)
>  memremap_pages+0x74c/0xa30
>  devm_memremap_pages+0x3c/0xa0
>  pmem_attach_disk+0x188/0x770
>  nvdimm_bus_probe+0xd8/0x470
>  really_probe+0x148/0x570
>  driver_probe_device+0x19c/0x1d0
>  device_driver_attach+0xcc/0x100
>  bind_store+0x134/0x1c0
>  drv_attr_store+0x44/0x60
>  sysfs_kf_write+0x74/0xc0
>  kernfs_fop_write+0x1b4/0x290
>  __vfs_write+0x3c/0x70
>  vfs_write+0xd0/0x260
>  ksys_write+0xdc/0x130
>  system_call+0x5c/0x68
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  arch/arm64/mm/flush.c     | 11 +++++++++++
>  arch/powerpc/lib/pmem.c   | 21 +++++++++++++++++++--
>  arch/x86/mm/pageattr.c    | 12 ++++++++++++
>  include/linux/libnvdimm.h |  1 +
>  4 files changed, 43 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> index ac485163a4a7..90c54c600023 100644
> --- a/arch/arm64/mm/flush.c
> +++ b/arch/arm64/mm/flush.c
> @@ -91,4 +91,15 @@ void arch_invalidate_pmem(void *addr, size_t size)
>         __inval_dcache_area(addr, size);
>  }
>  EXPORT_SYMBOL_GPL(arch_invalidate_pmem);
> +
> +unsigned long arch_validate_namespace_size(unsigned int ndr_mappings, unsigned long size)
> +{
> +       u32 remainder;
> +
> +       div_u64_rem(size, PAGE_SIZE * ndr_mappings, &remainder);
> +       if (remainder)
> +               return PAGE_SIZE * ndr_mappings;
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(arch_validate_namespace_size);
>  #endif
> diff --git a/arch/powerpc/lib/pmem.c b/arch/powerpc/lib/pmem.c
> index 377712e85605..2e661a08dae5 100644
> --- a/arch/powerpc/lib/pmem.c
> +++ b/arch/powerpc/lib/pmem.c
> @@ -17,14 +17,31 @@ void arch_wb_cache_pmem(void *addr, size_t size)
>         unsigned long start = (unsigned long) addr;
>         flush_dcache_range(start, start + size);
>  }
> -EXPORT_SYMBOL(arch_wb_cache_pmem);
> +EXPORT_SYMBOL_GPL(arch_wb_cache_pmem);
>
>  void arch_invalidate_pmem(void *addr, size_t size)
>  {
>         unsigned long start = (unsigned long) addr;
>         flush_dcache_range(start, start + size);
>  }
> -EXPORT_SYMBOL(arch_invalidate_pmem);
> +EXPORT_SYMBOL_GPL(arch_invalidate_pmem);
> +
> +unsigned long arch_validate_namespace_size(unsigned int ndr_mappings, unsigned long size)
> +{
> +       u32 remainder;
> +       unsigned long linear_map_size;
> +
> +       if (radix_enabled())
> +               linear_map_size = PAGE_SIZE;
> +       else
> +               linear_map_size = (1UL << mmu_psize_defs[mmu_linear_psize].shift);

This seems more a "supported_alignments" problem, and less a namespace
size or PAGE_SIZE problem, because if the starting address is
misaligned this size validation can still succeed when it shouldn't.

One problem is that __size_store() does not validate the size against
the namespace alignment.

However, the next problem is that alignment is a property of the pfn
device, but not the raw namespace. I think this alignment constraint
should be captured by exposing "align" and "supported_alignments" at
the namespace level as the minimum alignment. The pfn level alignment
could then be an additional alignment constraint, but ndctl would
likely set them to the same value.

The "* ndr_mappings" constraint should be left out of the interface,
because that's a side effect of supporting namespace-type-blk aliasing
which no platform seems to do in practice. If for some strange reason
it's need in the future I'd rather expose the "aliasing" property
rather than fold it into the align / supported_aligns interface.
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