[PATCH] x86, pmem: use memcpy_mcsafe() for memcpy_from_pmem()

[Dan Williams]

Update the definition of memcpy_from_pmem() to return 0 or -EIO on
error.  Implement x86::arch_memcpy_from_pmem() with memcpy_mcsafe().

Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
Note that this patch is built on a merge of tip/ras/core, tip/x86/asm, and
nvdimm/for-4.6/acpi6.1 for the following reasons (respectively):

1/ memcpy_mcsafe() itself

2/ X86_FEATURE_MCE_RECOVERY cpu capability

3/ merge with the new 'clear poison' implementation:
   https://lists.01.org/pipermail/linux-nvdimm/2016-March/004826.html

 arch/x86/include/asm/pmem.h |    9 +++++++++
 drivers/nvdimm/pmem.c       |    4 ++--
 include/linux/pmem.h        |   14 ++++++++------
 3 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
index bf8b35d2035a..4df3820535c6 100644
--- a/arch/x86/include/asm/pmem.h
+++ b/arch/x86/include/asm/pmem.h
@@ -47,6 +47,15 @@ static inline void arch_memcpy_to_pmem(void __pmem *dst, const void *src,
 		BUG();
 }
 
+static inline int arch_memcpy_from_pmem(void *dst, const void __pmem *src,
+		size_t n)
+{
+	if (static_cpu_has(X86_FEATURE_MCE_RECOVERY))
+		return memcpy_mcsafe(dst, (void __force *) src, n) ? 0 : -EIO;
+	memcpy(dst, (void __force *) src, n);
+	return 0;
+}
+
 /**
  * arch_wmb_pmem - synchronize writes to persistent memory
  *
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index adc387236fe7..2022d08c60ce 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -98,7 +98,7 @@ static int pmem_do_bvec(struct pmem_device *pmem, struct page *page,
 		if (unlikely(bad_pmem))
 			rc = -EIO;
 		else {
-			memcpy_from_pmem(mem + off, pmem_addr, len);
+			rc = memcpy_from_pmem(mem + off, pmem_addr, len);
 			flush_dcache_page(page);
 		}
 	} else {
@@ -295,7 +295,7 @@ static int pmem_rw_bytes(struct nd_namespace_common *ndns,
 
 		if (unlikely(is_bad_pmem(&pmem->bb, offset / 512, sz_align)))
 			return -EIO;
-		memcpy_from_pmem(buf, pmem->virt_addr + offset, size);
+		return memcpy_from_pmem(buf, pmem->virt_addr + offset, size);
 	} else {
 		memcpy_to_pmem(pmem->virt_addr + offset, buf, size);
 		wmb_pmem();
diff --git a/include/linux/pmem.h b/include/linux/pmem.h
index 3ec5309e29f3..c46c5cf6538e 100644
--- a/include/linux/pmem.h
+++ b/include/linux/pmem.h
@@ -66,14 +66,16 @@ static inline void arch_invalidate_pmem(void __pmem *addr, size_t size)
 #endif
 
 /*
- * Architectures that define ARCH_HAS_PMEM_API must provide
- * implementations for arch_memcpy_to_pmem(), arch_wmb_pmem(),
- * arch_copy_from_iter_pmem(), arch_clear_pmem(), arch_wb_cache_pmem()
- * and arch_has_wmb_pmem().
+ * memcpy_from_pmem - read from persistent memory with error handling
+ * @dst: destination buffer
+ * @src: source buffer
+ *
+ * Returns 0 on success -EIO on failure.
  */
-static inline void memcpy_from_pmem(void *dst, void __pmem const *src, size_t size)
+static inline int memcpy_from_pmem(void *dst, void __pmem const *src,
+		size_t size)
 {
-	memcpy(dst, (void __force const *) src, size);
+	return arch_memcpy_from_pmem(dst, src, size);
 }
 
 static inline bool arch_has_pmem_api(void)