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authorDan Williams <dan.j.williams@intel.com>2017-05-29 12:22:50 -0700
committerDan Williams <dan.j.williams@intel.com>2017-06-09 09:09:56 -0700
commit0aed55af88345b5d673240f90e671d79662fb01e (patch)
treeb4ebcb7d95e47a7fef48558daafc0e527c1e60ca /lib
parent3c2993b8c6143d8a5793746a54eba8f86f95240f (diff)
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 'lib')
-rw-r--r--lib/Kconfig3
-rw-r--r--lib/iov_iter.c22
2 files changed, 25 insertions, 0 deletions
diff --git a/lib/Kconfig b/lib/Kconfig
index 0c8b78a9ae2e..2d1c4b3a085c 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -548,6 +548,9 @@ config ARCH_HAS_SG_CHAIN
config ARCH_HAS_PMEM_API
bool
+config ARCH_HAS_UACCESS_FLUSHCACHE
+ bool
+
config ARCH_HAS_MMIO_FLUSH
bool
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index f835964c9485..c9a69064462f 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -615,6 +615,28 @@ size_t copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
}
EXPORT_SYMBOL(copy_from_iter_nocache);
+#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
+size_t copy_from_iter_flushcache(void *addr, size_t bytes, struct iov_iter *i)
+{
+ char *to = addr;
+ if (unlikely(i->type & ITER_PIPE)) {
+ WARN_ON(1);
+ return 0;
+ }
+ iterate_and_advance(i, bytes, v,
+ __copy_from_user_flushcache((to += v.iov_len) - v.iov_len,
+ v.iov_base, v.iov_len),
+ memcpy_page_flushcache((to += v.bv_len) - v.bv_len, v.bv_page,
+ v.bv_offset, v.bv_len),
+ memcpy_flushcache((to += v.iov_len) - v.iov_len, v.iov_base,
+ v.iov_len)
+ )
+
+ return bytes;
+}
+EXPORT_SYMBOL_GPL(copy_from_iter_flushcache);
+#endif
+
bool copy_from_iter_full_nocache(void *addr, size_t bytes, struct iov_iter *i)
{
char *to = addr;