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authorDan Williams <dan.j.williams@intel.com>2017-05-29 22:22:50 +0300
committerDan Williams <dan.j.williams@intel.com>2017-06-09 19:09:56 +0300
commit0aed55af88345b5d673240f90e671d79662fb01e (patch)
treeb4ebcb7d95e47a7fef48558daafc0e527c1e60ca /include
parent3c2993b8c6143d8a5793746a54eba8f86f95240f (diff)
downloadlinux-0aed55af88345b5d673240f90e671d79662fb01e.tar.xz
x86, uaccess: introduce copy_from_iter_flushcache for pmem / cache-bypass operations
The pmem driver has a need to transfer data with a persistent memory destination and be able to rely on the fact that the destination writes are not cached. It is sufficient for the writes to be flushed to a cpu-store-buffer (non-temporal / "movnt" in x86 terms), as we expect userspace to call fsync() to ensure data-writes have reached a power-fail-safe zone in the platform. The fsync() triggers a REQ_FUA or REQ_FLUSH to the pmem driver which will turn around and fence previous writes with an "sfence". Implement a __copy_from_user_inatomic_flushcache, memcpy_page_flushcache, and memcpy_flushcache, that guarantee that the destination buffer is not dirty in the cpu cache on completion. The new copy_from_iter_flushcache and sub-routines will be used to replace the "pmem api" (include/linux/pmem.h + arch/x86/include/asm/pmem.h). The availability of copy_from_iter_flushcache() and memcpy_flushcache() are gated by the CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE config symbol, and fallback to copy_from_iter_nocache() and plain memcpy() otherwise. This is meant to satisfy the concern from Linus that if a driver wants to do something beyond the normal nocache semantics it should be something private to that driver [1], and Al's concern that anything uaccess related belongs with the rest of the uaccess code [2]. The first consumer of this interface is a new 'copy_from_iter' dax operation so that pmem can inject cache maintenance operations without imposing this overhead on other dax-capable drivers. [1]: https://lists.01.org/pipermail/linux-nvdimm/2017-January/008364.html [2]: https://lists.01.org/pipermail/linux-nvdimm/2017-April/009942.html Cc: <x86@kernel.org> Cc: Jan Kara <jack@suse.cz> Cc: Jeff Moyer <jmoyer@redhat.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Toshi Kani <toshi.kani@hpe.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Matthew Wilcox <mawilcox@microsoft.com> Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/dax.h3
-rw-r--r--include/linux/string.h6
-rw-r--r--include/linux/uio.h15
3 files changed, 24 insertions, 0 deletions
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 5ec1f6c47716..bbe79ed90e2b 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -16,6 +16,9 @@ struct dax_operations {
*/
long (*direct_access)(struct dax_device *, pgoff_t, long,
void **, pfn_t *);
+ /* copy_from_iter: dax-driver override for default copy_from_iter */
+ size_t (*copy_from_iter)(struct dax_device *, pgoff_t, void *, size_t,
+ struct iov_iter *);
};
#if IS_ENABLED(CONFIG_DAX)
diff --git a/include/linux/string.h b/include/linux/string.h
index 537918f8a98e..7439d83eaa33 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -122,6 +122,12 @@ static inline __must_check int memcpy_mcsafe(void *dst, const void *src,
return 0;
}
#endif
+#ifndef __HAVE_ARCH_MEMCPY_FLUSHCACHE
+static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt)
+{
+ memcpy(dst, src, cnt);
+}
+#endif
void *memchr_inv(const void *s, int c, size_t n);
char *strreplace(char *s, char old, char new);
diff --git a/include/linux/uio.h b/include/linux/uio.h
index f2d36a3d3005..55cd54a0e941 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -95,6 +95,21 @@ size_t copy_to_iter(const void *addr, size_t bytes, struct iov_iter *i);
size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
bool copy_from_iter_full(void *addr, size_t bytes, struct iov_iter *i);
size_t copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i);
+#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
+/*
+ * Note, users like pmem that depend on the stricter semantics of
+ * copy_from_iter_flushcache() than copy_from_iter_nocache() must check for
+ * IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) before assuming that the
+ * destination is flushed from the cache on return.
+ */
+size_t copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i);
+#else
+static inline size_t copy_from_iter_flushcache(void *addr, size_t bytes,
+ struct iov_iter *i)
+{
+ return copy_from_iter_nocache(addr, bytes, i);
+}
+#endif
bool copy_from_iter_full_nocache(void *addr, size_t bytes, struct iov_iter *i);
size_t iov_iter_zero(size_t bytes, struct iov_iter *);
unsigned long iov_iter_alignment(const struct iov_iter *i);