x86/asm/memcpy_mcsafe: Return bytes remaining

Machine check safe memory copies are currently deployed in the pmem
driver whenever reading from persistent memory media, so that -EIO is
returned rather than triggering a kernel panic. While this protects most
pmem accesses, it is not complete in the filesystem-dax case. When
filesystem-dax is enabled reads may bypass the block layer and the
driver via dax_iomap_actor() and its usage of copy_to_iter().

In preparation for creating a copy_to_iter() variant that can handle
machine checks, teach memcpy_mcsafe() to return the number of bytes
remaining rather than -EFAULT when an exception occurs.

Co-developed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: hch@lst.de
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-nvdimm@lists.01.org
Link: http://lkml.kernel.org/r/152539238119.31796.14318473522414462886.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/string_64.h b/arch/x86/include/asm/string_64.h
index 4752f89..d33f92b 100644 (file)
--- 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(void *dst, const void *src, size_t cnt);
+__must_check unsigned long __memcpy_mcsafe(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/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
index 5709f3e..f01a883 100644 (file)
--- a/arch/x86/lib/memcpy_64.S
+++ b/arch/x86/lib/memcpy_64.S
@@ -252,14 +252,22 @@ ENDPROC(__memcpy_mcsafe)
 EXPORT_SYMBOL_GPL(__memcpy_mcsafe)
 
        .section .fixup, "ax"
-       /* Return -EFAULT for any failure */
-.L_memcpy_mcsafe_fail:
-       mov     $-EFAULT, %rax
+       /*
+        * Return number of bytes not copied for any failure. Note that
+        * there is no "tail" handling since the source buffer is 8-byte
+        * aligned and poison is cacheline aligned.
+        */
+.E_read_words:
+       shll    $3, %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_read_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_read_words, .E_read_words)
+       _ASM_EXTABLE_FAULT(.L_read_trailing_bytes, .E_trailing_bytes)
 #endif

diff --git a/drivers/nvdimm/claim.c b/drivers/nvdimm/claim.c
index 3085227..2e96b34 100644 (file)
--- 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 9d71492..e023d6a 100644 (file)
--- 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 dd39a69..4a5a0eb 100644 (file)
--- 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;