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x86, pmem: clarify that ARCH_HAS_PMEM_API implies PMEM mapped WB

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Given that a write-back (WB) mapping plus non-temporal stores is
expected to be the most efficient way to access PMEM, update the
definition of ARCH_HAS_PMEM_API to imply arch support for
WB-mapped-PMEM.  This is needed as a pre-requisite for adding PMEM to
the direct map and mapping it with struct page.

The above clarification for X86_64 means that memcpy_to_pmem() is
permitted to use the non-temporal arch_memcpy_to_pmem() rather than
needlessly fall back to default_memcpy_to_pmem() when the pcommit
instruction is not available.  When arch_memcpy_to_pmem() is not
guaranteed to flush writes out of cache, i.e. on older X86_32
implementations where non-temporal stores may just dirty cache,
ARCH_HAS_PMEM_API is simply disabled.

The default fall back for persistent memory handling remains.  Namely,
map it with the WT (write-through) cache-type and hope for the best.

arch_has_pmem_api() is updated to only indicate whether the arch
provides the proper helpers to meet the minimum "writes are visible
outside the cache hierarchy after memcpy_to_pmem() + wmb_pmem()".  Code
that cares whether wmb_pmem() actually flushes writes to pmem must now
call arch_has_wmb_pmem() directly.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
[hch: set ARCH_HAS_PMEM_API=n on x86_32]
Reviewed-by: Christoph Hellwig <hch@lst.de>
[toshi: x86_32 compile fixes]
Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams 2015-08-24 18:29:38 -04:00
parent 41e94a8513
commit 96601adb74
5 changed files with 28 additions and 26 deletions
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2
arch/x86/Kconfig
View file

@ -27,7 +27,7 @@ config X86
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_FAST_MULTIPLIER
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_PMEM_API
select ARCH_HAS_PMEM_API if X86_64
select ARCH_HAS_MMIO_FLUSH
select ARCH_HAS_SG_CHAIN
select ARCH_HAVE_NMI_SAFE_CMPXCHG

9
arch/x86/include/asm/pmem.h
View file

@ -18,8 +18,6 @@
#include <asm/cpufeature.h>
#include <asm/special_insns.h>
#define ARCH_MEMREMAP_PMEM MEMREMAP_WB
#ifdef CONFIG_ARCH_HAS_PMEM_API
/**
* arch_memcpy_to_pmem - copy data to persistent memory
@ -143,18 +141,13 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
__arch_wb_cache_pmem(vaddr, size);
}
static inline bool arch_has_wmb_pmem(void)
static inline bool __arch_has_wmb_pmem(void)
{
#ifdef CONFIG_X86_64
/*
* We require that wmb() be an 'sfence', that is only guaranteed on
* 64-bit builds
*/
return static_cpu_has(X86_FEATURE_PCOMMIT);
#else
return false;
#endif
}
#endif /* CONFIG_ARCH_HAS_PMEM_API */
#endif /* __ASM_X86_PMEM_H__ */

3
drivers/acpi/nfit.c
View file

@ -20,6 +20,7 @@
#include <linux/sort.h>
#include <linux/pmem.h>
#include <linux/io.h>
#include <asm/cacheflush.h>
#include "nfit.h"
/*
@ -1371,7 +1372,7 @@ static int acpi_nfit_blk_region_enable(struct nvdimm_bus *nvdimm_bus,
return -ENOMEM;
}
if (!arch_has_pmem_api() && !nfit_blk->nvdimm_flush)
if (!arch_has_wmb_pmem() && !nfit_blk->nvdimm_flush)
dev_warn(dev, "unable to guarantee persistence of writes\n");
if (mmio->line_size == 0)

2
drivers/nvdimm/pmem.c
View file

@ -125,7 +125,7 @@ static struct pmem_device *pmem_alloc(struct device *dev,
pmem->phys_addr = res->start;
pmem->size = resource_size(res);
if (!arch_has_pmem_api())
if (!arch_has_wmb_pmem())
dev_warn(dev, "unable to guarantee persistence of writes\n");
if (!devm_request_mem_region(dev, pmem->phys_addr, pmem->size,

38
include/linux/pmem.h
View file

@ -17,18 +17,25 @@
#include <linux/uio.h>
#ifdef CONFIG_ARCH_HAS_PMEM_API
#define ARCH_MEMREMAP_PMEM MEMREMAP_WB
#include <asm/pmem.h>
#else
#define ARCH_MEMREMAP_PMEM MEMREMAP_WT
/*
* These are simply here to enable compilation, all call sites gate
* calling these symbols with arch_has_pmem_api() and redirect to the
* implementation in asm/pmem.h.
*/
static inline bool __arch_has_wmb_pmem(void)
{
return false;
}
static inline void arch_wmb_pmem(void)
{
BUG();
}
static inline bool arch_has_wmb_pmem(void)
{
return false;
}
static inline void arch_memcpy_to_pmem(void __pmem *dst, const void *src,
size_t n)
{
@ -53,7 +60,6 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
* implementations for arch_memcpy_to_pmem(), arch_wmb_pmem(),
* arch_copy_from_iter_pmem(), arch_clear_pmem() and arch_has_wmb_pmem().
*/
static inline void memcpy_from_pmem(void *dst, void __pmem const *src, size_t size)
{
memcpy(dst, (void __force const *) src, size);
@ -64,8 +70,13 @@ static inline void memunmap_pmem(struct device *dev, void __pmem *addr)
devm_memunmap(dev, (void __force *) addr);
}
static inline bool arch_has_pmem_api(void)
{
return IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API);
}
/**
* arch_has_pmem_api - true if wmb_pmem() ensures durability
* arch_has_wmb_pmem - true if wmb_pmem() ensures durability
*
* For a given cpu implementation within an architecture it is possible
* that wmb_pmem() resolves to a nop. In the case this returns
@ -73,9 +84,9 @@ static inline void memunmap_pmem(struct device *dev, void __pmem *addr)
* fall back to a different data consistency model, or otherwise notify
* the user.
*/
static inline bool arch_has_pmem_api(void)
static inline bool arch_has_wmb_pmem(void)
{
return IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API) && arch_has_wmb_pmem();
return arch_has_pmem_api() && __arch_has_wmb_pmem();
}
/*
@ -120,13 +131,8 @@ static inline void default_clear_pmem(void __pmem *addr, size_t size)
static inline void __pmem *memremap_pmem(struct device *dev,
resource_size_t offset, unsigned long size)
{
#ifdef ARCH_MEMREMAP_PMEM
return (void __pmem *) devm_memremap(dev, offset, size,
ARCH_MEMREMAP_PMEM);
#else
return (void __pmem *) devm_memremap(dev, offset, size,
MEMREMAP_WT);
#endif
}
/**
@ -158,8 +164,10 @@ static inline void memcpy_to_pmem(void __pmem *dst, const void *src, size_t n)
*/
static inline void wmb_pmem(void)
{
if (arch_has_pmem_api())
if (arch_has_wmb_pmem())
arch_wmb_pmem();
else
wmb();
}
/**