netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 127 insertions, 0 deletions

diff --git a/include/asm-generic/cacheflush.h b/include/asm-generic/cacheflush.h
new file mode 100644
index 000000000..7ee8a179d
--- /dev/null
+++ b/include/asm-generic/cacheflush.h
@@ -0,0 +1,127 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_CACHEFLUSH_H
+#define _ASM_GENERIC_CACHEFLUSH_H
+
+#include <linux/instrumented.h>
+
+struct mm_struct;
+struct vm_area_struct;
+struct page;
+struct address_space;
+
+/*
+ * The cache doesn't need to be flushed when TLB entries change when
+ * the cache is mapped to physical memory, not virtual memory
+ */
+#ifndef flush_cache_all
+static inline void flush_cache_all(void)
+{
+}
+#endif
+
+#ifndef flush_cache_mm
+static inline void flush_cache_mm(struct mm_struct *mm)
+{
+}
+#endif
+
+#ifndef flush_cache_dup_mm
+static inline void flush_cache_dup_mm(struct mm_struct *mm)
+{
+}
+#endif
+
+#ifndef flush_cache_range
+static inline void flush_cache_range(struct vm_area_struct *vma,
+				     unsigned long start,
+				     unsigned long end)
+{
+}
+#endif
+
+#ifndef flush_cache_page
+static inline void flush_cache_page(struct vm_area_struct *vma,
+				    unsigned long vmaddr,
+				    unsigned long pfn)
+{
+}
+#endif
+
+#ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+static inline void flush_dcache_page(struct page *page)
+{
+}
+
+#define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0
+#endif
+
+#ifndef flush_dcache_mmap_lock
+static inline void flush_dcache_mmap_lock(struct address_space *mapping)
+{
+}
+#endif
+
+#ifndef flush_dcache_mmap_unlock
+static inline void flush_dcache_mmap_unlock(struct address_space *mapping)
+{
+}
+#endif
+
+#ifndef flush_icache_range
+static inline void flush_icache_range(unsigned long start, unsigned long end)
+{
+}
+#endif
+
+#ifndef flush_icache_user_range
+#define flush_icache_user_range flush_icache_range
+#endif
+
+#ifndef flush_icache_user_page
+static inline void flush_icache_user_page(struct vm_area_struct *vma,
+					   struct page *page,
+					   unsigned long addr, int len)
+{
+}
+#endif
+
+#ifndef flush_cache_vmap
+static inline void flush_cache_vmap(unsigned long start, unsigned long end)
+{
+}
+#endif
+
+#ifndef flush_cache_vmap_early
+static inline void flush_cache_vmap_early(unsigned long start, unsigned long end)
+{
+}
+#endif
+
+#ifndef flush_cache_vunmap
+static inline void flush_cache_vunmap(unsigned long start, unsigned long end)
+{
+}
+#endif
+
+#ifndef copy_to_user_page
+#define copy_to_user_page(vma, page, vaddr, dst, src, len)	\
+	do { \
+		instrument_copy_to_user((void __user *)dst, src, len); \
+		memcpy(dst, src, len); \
+		flush_icache_user_page(vma, page, vaddr, len); \
+	} while (0)
+#endif
+
+
+#ifndef copy_from_user_page
+#define copy_from_user_page(vma, page, vaddr, dst, src, len)		  \
+	do {								  \
+		instrument_copy_from_user_before(dst, (void __user *)src, \
+						 len);			  \
+		memcpy(dst, src, len);					  \
+		instrument_copy_from_user_after(dst, (void __user *)src, len, \
+						0);			  \
+	} while (0)
+#endif
+
+#endif /* _ASM_GENERIC_CACHEFLUSH_H */