diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index 533f74c300c2..92ee5e187113 100644
--- a/arch/x86/include/asm/string_64.h
+++ b/arch/x86/include/asm/string_64.h
@@ -116,7 +116,8 @@ int strcmp(const char *cs, const char *ct);
 #endif
 
 #define __HAVE_ARCH_MEMCPY_MCSAFE 1
-__must_check int memcpy_mcsafe_unrolled(void *dst, const void *src, size_t cnt);
+__must_check unsigned long memcpy_mcsafe_unrolled(void *dst, const void *src,
+		size_t cnt);
 DECLARE_STATIC_KEY_FALSE(mcsafe_key);
 
 /**
@@ -131,9 +132,10 @@ DECLARE_STATIC_KEY_FALSE(mcsafe_key);
  * actually do machine check recovery. Everyone else can just
  * use memcpy().
  *
- * Return 0 for success, -EFAULT for fail
+ * Return 0 for success, or number of bytes not copied if there was an
+ * exception.
  */
-static __always_inline __must_check int
+static __always_inline __must_check unsigned long
 memcpy_mcsafe(void *dst, const void *src, size_t cnt)
 {
 #ifdef CONFIG_X86_MCE
diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
index 62546b3a398e..c064a77e8fcb 100644
--- a/arch/x86/include/asm/uaccess_64.h
+++ b/arch/x86/include/asm/uaccess_64.h
@@ -194,4 +194,7 @@ __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size)
 unsigned long
 copy_user_handle_tail(char *to, char *from, unsigned len);
 
+unsigned long
+mcsafe_handle_tail(char *to, char *from, unsigned len, unsigned limit);
+
 #endif /* _ASM_X86_UACCESS_64_H */
diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
index 6a416a7df8ee..97b772fcf62f 100644
--- a/arch/x86/lib/memcpy_64.S
+++ b/arch/x86/lib/memcpy_64.S
@@ -283,22 +283,79 @@ ENDPROC(memcpy_mcsafe_unrolled)
 EXPORT_SYMBOL_GPL(memcpy_mcsafe_unrolled)
 
 	.section .fixup, "ax"
-	/* Return -EFAULT for any failure */
-.L_memcpy_mcsafe_fail:
-	mov	$-EFAULT, %rax
+	/* Return number of bytes not copied for any failure */
+
+	/*
+	 * For .E_cache_{1,2,3} we have successfully read {8,16,24}
+	 * bytes before crossing into the poison cacheline. Arrange for
+	 * mcsafe_handle_tail to write those {8,16,24} bytes to the
+	 * destination without re-triggering the machine check. %ecx
+	 * contains the limit and %edx contains total bytes remaining.
+	 */
+.E_cache_1:
+	shll	$6, %ecx
+	addl	%ecx, %edx
+	movl	$8, %ecx
+	jmp mcsafe_handle_tail
+.E_cache_2:
+	shll	$6, %ecx
+	addl	%ecx, %edx
+	movl	$16, %ecx
+	jmp mcsafe_handle_tail
+.E_cache_3:
+	shll	$6, %ecx
+	addl	%ecx, %edx
+	movl	$24, %ecx
+	jmp mcsafe_handle_tail
+	/*
+	 * In contrast to .E_cache_{1,2,3}, .E_cache_{5,6,7} have
+	 * successfully copied 32-bytes before crossing into the
+	 * poisoned cacheline.
+	 */
+.E_cache_5:
+	shll	$6, %ecx
+	addl	%ecx, %edx
+	movl	$8, %ecx
+	jmp .E_cache_upper
+.E_cache_6:
+	shll	$6, %ecx
+	addl	%ecx, %edx
+	movl	$16, %ecx
+	jmp .E_cache_upper
+.E_cache_7:
+	shll	$6, %ecx
+	addl	%ecx, %edx
+	movl	$24, %ecx
+	jmp .E_cache_upper
+.E_cache_upper:
+	addq	$32, %rsi
+	addq	$32, %rdi
+	subl	$32, %edx
+	jmp mcsafe_handle_tail
+.E_trailing_words:
+	shll	$3, %ecx
+	jmp .E_leading_bytes
+.E_cache_4:
+	subl	$32, %edx
+.E_cache_0:
+	shll	$6, %ecx
+.E_leading_bytes:
+	addl	%edx, %ecx
+.E_trailing_bytes:
+	mov	%ecx, %eax
 	ret
 
 	.previous
 
-	_ASM_EXTABLE_FAULT(.L_read_leading_bytes, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_cache_r0, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_cache_r1, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_cache_r2, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_cache_r3, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_cache_r4, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_cache_r5, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_cache_r6, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_cache_r7, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_read_trailing_words, .L_memcpy_mcsafe_fail)
-	_ASM_EXTABLE_FAULT(.L_read_trailing_bytes, .L_memcpy_mcsafe_fail)
+	_ASM_EXTABLE_FAULT(.L_read_leading_bytes, .E_leading_bytes)
+	_ASM_EXTABLE_FAULT(.L_cache_r0, .E_cache_0)
+	_ASM_EXTABLE_FAULT(.L_cache_r1, .E_cache_1)
+	_ASM_EXTABLE_FAULT(.L_cache_r2, .E_cache_2)
+	_ASM_EXTABLE_FAULT(.L_cache_r3, .E_cache_3)
+	_ASM_EXTABLE_FAULT(.L_cache_r4, .E_cache_4)
+	_ASM_EXTABLE_FAULT(.L_cache_r5, .E_cache_5)
+	_ASM_EXTABLE_FAULT(.L_cache_r6, .E_cache_6)
+	_ASM_EXTABLE_FAULT(.L_cache_r7, .E_cache_7)
+	_ASM_EXTABLE_FAULT(.L_read_trailing_words, .E_trailing_words)
+	_ASM_EXTABLE_FAULT(.L_read_trailing_bytes, .E_trailing_bytes)
 #endif
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 75d3776123cc..e2bcc7d85436 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -75,6 +75,18 @@ copy_user_handle_tail(char *to, char *from, unsigned len)
 	return len;
 }
 
+__visible unsigned long
+mcsafe_handle_tail(char *to, char *from, unsigned len, unsigned limit)
+{
+	for (; len && limit; --len, --limit, to++) {
+		unsigned long rem = memcpy_mcsafe_unrolled(to, from, 1);
+
+		if (rem)
+			break;
+	}
+	return len;
+}
+
 #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
 /**
  * clean_cache_range - write back a cache range with CLWB
diff --git a/drivers/nvdimm/claim.c b/drivers/nvdimm/claim.c
index 30852270484f..2e96b34bc936 100644
--- a/drivers/nvdimm/claim.c
+++ b/drivers/nvdimm/claim.c
@@ -276,7 +276,8 @@ static int nsio_rw_bytes(struct nd_namespace_common *ndns,
 	if (rw == READ) {
 		if (unlikely(is_bad_pmem(&nsio->bb, sector, sz_align)))
 			return -EIO;
-		return memcpy_mcsafe(buf, nsio->addr + offset, size);
+		if (memcpy_mcsafe(buf, nsio->addr + offset, size) != 0)
+			return -EIO;
 	}
 
 	if (unlikely(is_bad_pmem(&nsio->bb, sector, sz_align))) {
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 9d714926ecf5..e023d6aa22b5 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -101,15 +101,15 @@ static blk_status_t read_pmem(struct page *page, unsigned int off,
 		void *pmem_addr, unsigned int len)
 {
 	unsigned int chunk;
-	int rc;
+	unsigned long rem;
 	void *mem;
 
 	while (len) {
 		mem = kmap_atomic(page);
 		chunk = min_t(unsigned int, len, PAGE_SIZE);
-		rc = memcpy_mcsafe(mem + off, pmem_addr, chunk);
+		rem = memcpy_mcsafe(mem + off, pmem_addr, chunk);
 		kunmap_atomic(mem);
-		if (rc)
+		if (rem)
 			return BLK_STS_IOERR;
 		len -= chunk;
 		off = 0;
diff --git a/include/linux/string.h b/include/linux/string.h
index dd39a690c841..4a5a0eb7df51 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -147,8 +147,8 @@ extern int memcmp(const void *,const void *,__kernel_size_t);
 extern void * memchr(const void *,int,__kernel_size_t);
 #endif
 #ifndef __HAVE_ARCH_MEMCPY_MCSAFE
-static inline __must_check int memcpy_mcsafe(void *dst, const void *src,
-		size_t cnt)
+static inline __must_check unsigned long memcpy_mcsafe(void *dst,
+		const void *src, size_t cnt)
 {
 	memcpy(dst, src, cnt);
 	return 0;
