Re: [PATCH v4 1/6] libnvdimm/namespace: Make namespace size validation arch dependent

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

On Mon, Jan 20, 2020 at 6:08 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, users 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
>
> Kernel should also ensure that namespace size is also mulitple of subsection size.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  arch/arm64/mm/flush.c     | 6 ++++++
>  arch/powerpc/lib/pmem.c   | 9 +++++++++
>  arch/x86/mm/pageattr.c    | 7 +++++++
>  include/linux/libnvdimm.h | 1 +
>  4 files changed, 23 insertions(+)
>
> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> index ac485163a4a7..95cb5538bc6e 100644
> --- a/arch/arm64/mm/flush.c
> +++ b/arch/arm64/mm/flush.c
> @@ -91,4 +91,10 @@ void arch_invalidate_pmem(void *addr, size_t size)
>         __inval_dcache_area(addr, size);
>  }
>  EXPORT_SYMBOL_GPL(arch_invalidate_pmem);
> +
> +unsigned long arch_namespace_map_size(void)
> +{
> +       return PAGE_SIZE;
> +}
> +EXPORT_SYMBOL_GPL(arch_namespace_map_size);
>  #endif
> diff --git a/arch/powerpc/lib/pmem.c b/arch/powerpc/lib/pmem.c
> index 0666a8d29596..63dca24e4a18 100644
> --- a/arch/powerpc/lib/pmem.c
> +++ b/arch/powerpc/lib/pmem.c
> @@ -26,6 +26,15 @@ void arch_invalidate_pmem(void *addr, size_t size)
>  }
>  EXPORT_SYMBOL_GPL(arch_invalidate_pmem);
>
> +unsigned long arch_namespace_map_size(void)
> +{
> +       if (radix_enabled())
> +               return PAGE_SIZE;
> +       return (1UL << mmu_psize_defs[mmu_linear_psize].shift);
> +
> +}
> +EXPORT_SYMBOL_GPL(arch_namespace_map_size);
> +
>  /*
>   * CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE symbols
>   */
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 1b99ad05b117..d78b5082f376 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -310,6 +310,13 @@ void arch_invalidate_pmem(void *addr, size_t size)
>  }
>  EXPORT_SYMBOL_GPL(arch_invalidate_pmem);
>
> +unsigned long arch_namespace_map_size(void)
> +{
> +       return PAGE_SIZE;
> +}
> +EXPORT_SYMBOL_GPL(arch_namespace_map_size);
> +
> +
>  static void __cpa_flush_all(void *arg)
>  {
>         unsigned long cache = (unsigned long)arg;
> diff --git a/include/linux/libnvdimm.h b/include/linux/libnvdimm.h
> index 9df091bd30ba..a3476dbd2656 100644
> --- a/include/linux/libnvdimm.h
> +++ b/include/linux/libnvdimm.h
> @@ -284,4 +284,5 @@ static inline void arch_invalidate_pmem(void *addr, size_t size)
>  }
>  #endif
>
> +unsigned long arch_namespace_map_size(void);

This property is more generic than the nvdimm namespace mapping size,
it's more the fundamental remap granularity that the architecture
supports. So I would expect this to be defined in core header files.
Something like:

diff --git a/include/linux/io.h b/include/linux/io.h
index a59834bc0a11..58b3b2091dbb 100644
--- a/include/linux/io.h
+++ b/include/linux/io.h
@@ -155,6 +155,13 @@ enum {
 void *memremap(resource_size_t offset, size_t size, unsigned long flags);
 void memunmap(void *addr);

+#ifndef memremap_min_align
+static inline unsigned int memremap_min_align(void)
+{
+       return PAGE_SIZE;
+}
+#endif
+
 /*
  * On x86 PAT systems we have memory tracking that keeps track of
  * the allowed mappings on memory ranges. This tracking works for

...and then have a definition is asm/io.h like this:

unsigned int memremap_min_align(void);
#define memremap_min_align memremap_min_align

That way only architectures that want to opt out of the default need
to define something in their local header.
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