lib/iov_iter: Fix pipe handling in _copy_to_iter_mcsafe()

By mistake the ITER_PIPE early-exit / warning from copy_from_iter() was
cargo-culted in _copy_to_iter_mcsafe() rather than a machine-check-safe
version of copy_to_iter_pipe().

Implement copy_pipe_to_iter_mcsafe() being careful to return the
indication of short copies due to a CPU exception.

Without this regression-fix all splice reads to dax-mode files fail.

Reported-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Tested-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: 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>
Fixes: 8780356ef630 ("x86/asm/memcpy_mcsafe: Define copy_to_iter_mcsafe()")
Link: http://lkml.kernel.org/r/153108277278.37979.3327916996902264102.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 33 insertions, 4 deletions

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 09fb73ad9d54..8be175df3075 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -596,6 +596,37 @@ static unsigned long memcpy_mcsafe_to_page(struct page *page, size_t offset,
         return ret;
 }
 
+static size_t copy_pipe_to_iter_mcsafe(const void *addr, size_t bytes,
+                                struct iov_iter *i)
+{
+        struct pipe_inode_info *pipe = i->pipe;
+        size_t n, off, xfer = 0;
+        int idx;
+
+        if (!sanity(i))
+                return 0;
+
+        bytes = n = push_pipe(i, bytes, &idx, &off);
+        if (unlikely(!n))
+                return 0;
+        for ( ; n; idx = next_idx(idx, pipe), off = 0) {
+                size_t chunk = min_t(size_t, n, PAGE_SIZE - off);
+                unsigned long rem;
+
+                rem = memcpy_mcsafe_to_page(pipe->bufs[idx].page, off, addr,
+                                chunk);
+                i->idx = idx;
+                i->iov_offset = off + chunk - rem;
+                xfer += chunk - rem;
+                if (rem)
+                        break;
+                n -= chunk;
+                addr += chunk;
+        }
+        i->count -= xfer;
+        return xfer;
+}
+
 /**
  * _copy_to_iter_mcsafe - copy to user with source-read error exception handling
  * @addr: source kernel address
@@ -627,10 +658,8 @@ size_t _copy_to_iter_mcsafe(const void *addr, size_t bytes, struct iov_iter *i)
         const char *from = addr;
         unsigned long rem, curr_addr, s_addr = (unsigned long) addr;
 
-        if (unlikely(i->type & ITER_PIPE)) {
-                WARN_ON(1);
-                return 0;
-        }
+        if (unlikely(i->type & ITER_PIPE))
+                return copy_pipe_to_iter_mcsafe(addr, bytes, i);
         if (iter_is_iovec(i))
                 might_fault();
         iterate_and_advance(i, bytes, v,