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mm/memremap_pages: Introduce memremap_compat_align()

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The "sub-section memory hotplug" facility allows memremap_pages() users
like libnvdimm to compensate for hardware platforms like x86 that have a
section size larger than their hardware memory mapping granularity.  The
compensation that sub-section support affords is being tolerant of
physical memory resources shifting by units smaller (64MiB on x86) than
the memory-hotplug section size (128 MiB). Where the platform
physical-memory mapping granularity is limited by the number and
capability of address-decode-registers in the memory controller.

While the sub-section support allows memremap_pages() to operate on
sub-section (2MiB) granularity, the Power architecture may still
require 16MiB alignment on "!radix_enabled()" platforms.

In order for libnvdimm to be able to detect and manage this per-arch
limitation, introduce memremap_compat_align() as a common minimum
alignment across all driver-facing memory-mapping interfaces, and let
Power override it to 16MiB in the "!radix_enabled()" case.

The assumption / requirement for 16MiB to be a viable
memremap_compat_align() value is that Power does not have platforms
where its equivalent of address-decode-registers never hardware remaps a
persistent memory resource on smaller than 16MiB boundaries. Note that I
tried my best to not add a new Kconfig symbol, but header include
entanglements defeated the #ifndef memremap_compat_align design pattern
and the need to export it defeats the __weak design pattern for arch
overrides.

Based on an initial patch by Aneesh.

Link: http://lore.kernel.org/r/CAPcyv4gBGNP95APYaBcsocEa50tQj9b5h__83vgngjq3ouGX_Q@mail.gmail.com
Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams
2020-01-30 12:06:07 -08:00
parent 1d0827b75e
commit 9ffc1d19fc
7 changed files with 58 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
arch/powerpc/mm/ioremap.c
View File

@@ -2,6 +2,7 @@
#include <linux/io.h>
#include <linux/slab.h>
#include <linux/mmzone.h>
#include <linux/vmalloc.h>
#include <asm/io-workarounds.h>
@@ -97,3 +98,23 @@ void __iomem *do_ioremap(phys_addr_t pa, phys_addr_t offset, unsigned long size,
return NULL;
}
#ifdef CONFIG_ZONE_DEVICE
/*
* Override the generic version in mm/memremap.c.
*
* With hash translation, the direct-map range is mapped with just one
* page size selected by htab_init_page_sizes(). Consult
* mmu_psize_defs[] to determine the minimum page size alignment.
*/
unsigned long memremap_compat_align(void)
{
unsigned int shift = mmu_psize_defs[mmu_linear_psize].shift;
if (radix_enabled())
return SUBSECTION_SIZE;
return max(SUBSECTION_SIZE, 1UL << shift);
}
EXPORT_SYMBOL_GPL(memremap_compat_align);
#endif