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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 <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Reviewed-by: Ross Zwisler <[email protected]>
[hch: set ARCH_HAS_PMEM_API=n on x86_32]
Reviewed-by: Christoph Hellwig <[email protected]>
[toshi: x86_32 compile fixes]
Signed-off-by: Toshi Kani <[email protected]>
Signed-off-by: Dan Williams <[email protected]>
This commit is contained in:
Dan Williams 2015-08-24 18:29:38 -04:00
commit 96601adb74
5 changed files with 27 additions and 25 deletions
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3
drivers/acpi/nfit.c
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@ -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)