x86, pmem: use memcpy_mcsafe() for memcpy_from_pmem()

Update the definition of memcpy_from_pmem() to return 0 or a negative
error code. Implement x86/arch_memcpy_from_pmem() with memcpy_mcsafe().

Cc: Borislav Petkov <[e-mail]>
Cc: Tony Luck <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Acked-by: Ingo Molnar <[e-mail]>
Reviewed-by: Ross Zwisler <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>

arch/x86/include/asm/pmem.h

···
 		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);
+	memcpy(dst, (void __force *) src, n);
+	return 0;
+}
+
 /**
  * arch_wmb_pmem - synchronize writes to persistent memory
  *

drivers/nvdimm/pmem.c

···
 		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 {
···
 
 		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();

include/linux/pmem.h

···
 	BUG();
 }
 
+static inline int arch_memcpy_from_pmem(void *dst, const void __pmem *src,
+		size_t n)
+{
+	BUG();
+	return -EFAULT;
+}
+
 static inline size_t arch_copy_from_iter_pmem(void __pmem *addr, size_t bytes,
 		struct iov_iter *i)
 {
···
 #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
+ * @size: transfer length
+ *
+ * Returns 0 on success negative error code 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)