[PATCH v4 1/5] mm/memremap_pages: Introduce memremap_compat_align()
Dan Williams
dan.j.williams at intel.com
Wed Mar 4 13:08:08 AEDT 2020
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 at linux.ibm.com>
Reported-by: Jeff Moyer <jmoyer at redhat.com>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Paul Mackerras <paulus at samba.org>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
Signed-off-by: Dan Williams <dan.j.williams at intel.com>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/mm/ioremap.c | 21 +++++++++++++++++++++
drivers/nvdimm/pfn_devs.c | 2 +-
include/linux/memremap.h | 8 ++++++++
include/linux/mmzone.h | 1 +
lib/Kconfig | 3 +++
mm/memremap.c | 23 +++++++++++++++++++++++
7 files changed, 58 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 497b7d0b2d7e..e6ffe905e2b9 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -122,6 +122,7 @@ config PPC
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_KCOV
select ARCH_HAS_HUGEPD if HUGETLB_PAGE
+ select ARCH_HAS_MEMREMAP_COMPAT_ALIGN
select ARCH_HAS_MMIOWB if PPC64
select ARCH_HAS_PHYS_TO_DMA
select ARCH_HAS_PMEM_API
diff --git a/arch/powerpc/mm/ioremap.c b/arch/powerpc/mm/ioremap.c
index fc669643ce6a..b1a0aebe8c48 100644
--- a/arch/powerpc/mm/ioremap.c
+++ b/arch/powerpc/mm/ioremap.c
@@ -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
diff --git a/drivers/nvdimm/pfn_devs.c b/drivers/nvdimm/pfn_devs.c
index b94f7a7e94b8..a5c25cb87116 100644
--- a/drivers/nvdimm/pfn_devs.c
+++ b/drivers/nvdimm/pfn_devs.c
@@ -750,7 +750,7 @@ static int nd_pfn_init(struct nd_pfn *nd_pfn)
start = nsio->res.start;
size = resource_size(&nsio->res);
npfns = PHYS_PFN(size - SZ_8K);
- align = max(nd_pfn->align, (1UL << SUBSECTION_SHIFT));
+ align = max(nd_pfn->align, SUBSECTION_SIZE);
end_trunc = start + size - ALIGN_DOWN(start + size, align);
if (nd_pfn->mode == PFN_MODE_PMEM) {
/*
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 6fefb09af7c3..8af1cbd8f293 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -132,6 +132,7 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
unsigned long vmem_altmap_offset(struct vmem_altmap *altmap);
void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns);
+unsigned long memremap_compat_align(void);
#else
static inline void *devm_memremap_pages(struct device *dev,
struct dev_pagemap *pgmap)
@@ -165,6 +166,12 @@ static inline void vmem_altmap_free(struct vmem_altmap *altmap,
unsigned long nr_pfns)
{
}
+
+/* when memremap_pages() is disabled all archs can remap a single page */
+static inline unsigned long memremap_compat_align(void)
+{
+ return PAGE_SIZE;
+}
#endif /* CONFIG_ZONE_DEVICE */
static inline void put_dev_pagemap(struct dev_pagemap *pgmap)
@@ -172,4 +179,5 @@ static inline void put_dev_pagemap(struct dev_pagemap *pgmap)
if (pgmap)
percpu_ref_put(pgmap->ref);
}
+
#endif /* _LINUX_MEMREMAP_H_ */
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 462f6873905a..6b77f7239af5 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1170,6 +1170,7 @@ static inline unsigned long section_nr_to_pfn(unsigned long sec)
#define SECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SECTION_MASK)
#define SUBSECTION_SHIFT 21
+#define SUBSECTION_SIZE (1UL << SUBSECTION_SHIFT)
#define PFN_SUBSECTION_SHIFT (SUBSECTION_SHIFT - PAGE_SHIFT)
#define PAGES_PER_SUBSECTION (1UL << PFN_SUBSECTION_SHIFT)
diff --git a/lib/Kconfig b/lib/Kconfig
index bc7e56370129..5d53f9609c25 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -615,6 +615,9 @@ config ARCH_HAS_PMEM_API
config MEMREGION
bool
+config ARCH_HAS_MEMREMAP_COMPAT_ALIGN
+ bool
+
# use memcpy to implement user copies for nommu architectures
config UACCESS_MEMCPY
bool
diff --git a/mm/memremap.c b/mm/memremap.c
index 09b5b7adc773..3e7afaf05639 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -7,6 +7,7 @@
#include <linux/mm.h>
#include <linux/pfn_t.h>
#include <linux/swap.h>
+#include <linux/mmzone.h>
#include <linux/swapops.h>
#include <linux/types.h>
#include <linux/wait_bit.h>
@@ -14,6 +15,28 @@
static DEFINE_XARRAY(pgmap_array);
+/*
+ * The memremap() and memremap_pages() interfaces are alternately used
+ * to map persistent memory namespaces. These interfaces place different
+ * constraints on the alignment and size of the mapping (namespace).
+ * memremap() can map individual PAGE_SIZE pages. memremap_pages() can
+ * only map subsections (2MB), and at least one architecture (PowerPC)
+ * the minimum mapping granularity of memremap_pages() is 16MB.
+ *
+ * The role of memremap_compat_align() is to communicate the minimum
+ * arch supported alignment of a namespace such that it can freely
+ * switch modes without violating the arch constraint. Namely, do not
+ * allow a namespace to be PAGE_SIZE aligned since that namespace may be
+ * reconfigured into a mode that requires SUBSECTION_SIZE alignment.
+ */
+#ifndef CONFIG_ARCH_HAS_MEMREMAP_COMPAT_ALIGN
+unsigned long memremap_compat_align(void)
+{
+ return SUBSECTION_SIZE;
+}
+EXPORT_SYMBOL_GPL(memremap_compat_align);
+#endif
+
#ifdef CONFIG_DEV_PAGEMAP_OPS
DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
EXPORT_SYMBOL(devmap_managed_key);
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