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SubjectRe: [PATCH v2 5/9] x86, pmem: push fallback handling to arch code
Date
On Wed, 2015-08-26 at 14:41 +0200, Christoph Hellwig wrote:
> I like the intent behind this, but not the implementation.
>
> I think the right approach is to keep the defaults in linux/pmem.h
> and simply not set CONFIG_ARCH_HAS_PMEM_API for x86-32.

Yes, that makes things much cleaner. Revised patch and changelog below:

8<----
Subject: x86, pmem: clarify that ARCH_HAS_PMEM_API implies PMEM mapped WB

From: Dan Williams <dan.j.williams@intel.com>

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>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Christoph Hellwig <hch@lst.de>
[hch: set ARCH_HAS_PMEM_API=n on X86_32]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
arch/x86/Kconfig | 2 +-
arch/x86/include/asm/io.h | 2 --
arch/x86/include/asm/pmem.h | 8 ++------
drivers/acpi/nfit.c | 2 +-
drivers/nvdimm/pmem.c | 2 +-
include/linux/pmem.h | 28 +++++++++++++++++-----------
6 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 76c61154ed50..5912859df533 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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_SG_CHAIN
select ARCH_HAVE_NMI_SAFE_CMPXCHG
select ARCH_MIGHT_HAVE_ACPI_PDC if ACPI
diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index d241fbd5c87b..83ec9b1d77cc 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -248,8 +248,6 @@ static inline void flush_write_buffers(void)
#endif
}

-#define ARCH_MEMREMAP_PMEM MEMREMAP_WB
-
#endif /* __KERNEL__ */

extern void native_io_delay(void);
diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
index a3a0df6545ee..5111f1f053a4 100644
--- a/arch/x86/include/asm/pmem.h
+++ b/arch/x86/include/asm/pmem.h
@@ -19,6 +19,7 @@
#include <asm/special_insns.h>

#ifdef CONFIG_ARCH_HAS_PMEM_API
+#define ARCH_MEMREMAP_PMEM MEMREMAP_WB
/**
* arch_memcpy_to_pmem - copy data to persistent memory
* @dst: destination buffer for the copy
@@ -141,18 +142,13 @@ 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__ */
diff --git a/drivers/acpi/nfit.c b/drivers/acpi/nfit.c
index 7c2638f914a9..c3fe20635562 100644
--- a/drivers/acpi/nfit.c
+++ b/drivers/acpi/nfit.c
@@ -1364,7 +1364,7 @@ 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)
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 3b5b9cb758b6..20bf122328da 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -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,
diff --git a/include/linux/pmem.h b/include/linux/pmem.h
index a9d84bf335ee..9ec42710315e 100644
--- a/include/linux/pmem.h
+++ b/include/linux/pmem.h
@@ -19,12 +19,12 @@
#ifdef CONFIG_ARCH_HAS_PMEM_API
#include <asm/pmem.h>
#else
-static inline void arch_wmb_pmem(void)
-{
- BUG();
-}
-
-static inline bool arch_has_wmb_pmem(void)
+/*
+ * 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;
}
@@ -53,7 +53,6 @@ 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 +63,13 @@ 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 +77,9 @@ 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();
}

/*
@@ -158,8 +162,10 @@ 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();
}

/**
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