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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 /arch/x86/lib/usercopy_64.c
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 'arch/x86/lib/usercopy_64.c')
-rw-r--r--arch/x86/lib/usercopy_64.c128
1 files changed, 128 insertions, 0 deletions
diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 3b7c40a2e3e1..f42d2fd86ca3 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -7,6 +7,7 @@
*/
#include <linux/export.h>
#include <linux/uaccess.h>
+#include <linux/highmem.h>
/*
* Zero Userspace
@@ -73,3 +74,130 @@ copy_user_handle_tail(char *to, char *from, unsigned len)
clac();
return len;
}
+
+#ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE
+/**
+ * clean_cache_range - write back a cache range with CLWB
+ * @vaddr: virtual start address
+ * @size: number of bytes to write back
+ *
+ * Write back a cache range using the CLWB (cache line write back)
+ * instruction. Note that @size is internally rounded up to be cache
+ * line size aligned.
+ */
+static void clean_cache_range(void *addr, size_t size)
+{
+ u16 x86_clflush_size = boot_cpu_data.x86_clflush_size;
+ unsigned long clflush_mask = x86_clflush_size - 1;
+ void *vend = addr + size;
+ void *p;
+
+ for (p = (void *)((unsigned long)addr & ~clflush_mask);
+ p < vend; p += x86_clflush_size)
+ clwb(p);
+}
+
+long __copy_user_flushcache(void *dst, const void __user *src, unsigned size)
+{
+ unsigned long flushed, dest = (unsigned long) dst;
+ long rc = __copy_user_nocache(dst, src, size, 0);
+
+ /*
+ * __copy_user_nocache() uses non-temporal stores for the bulk
+ * of the transfer, but we need to manually flush if the
+ * transfer is unaligned. A cached memory copy is used when
+ * destination or size is not naturally aligned. That is:
+ * - Require 8-byte alignment when size is 8 bytes or larger.
+ * - Require 4-byte alignment when size is 4 bytes.
+ */
+ if (size < 8) {
+ if (!IS_ALIGNED(dest, 4) || size != 4)
+ clean_cache_range(dst, 1);
+ } else {
+ if (!IS_ALIGNED(dest, 8)) {
+ dest = ALIGN(dest, boot_cpu_data.x86_clflush_size);
+ clean_cache_range(dst, 1);
+ }
+
+ flushed = dest - (unsigned long) dst;
+ if (size > flushed && !IS_ALIGNED(size - flushed, 8))
+ clean_cache_range(dst + size - 1, 1);
+ }
+
+ return rc;
+}
+
+void memcpy_flushcache(void *_dst, const void *_src, size_t size)
+{
+ unsigned long dest = (unsigned long) _dst;
+ unsigned long source = (unsigned long) _src;
+
+ /* cache copy and flush to align dest */
+ if (!IS_ALIGNED(dest, 8)) {
+ unsigned len = min_t(unsigned, size, ALIGN(dest, 8) - dest);
+
+ memcpy((void *) dest, (void *) source, len);
+ clean_cache_range((void *) dest, len);
+ dest += len;
+ source += len;
+ size -= len;
+ if (!size)
+ return;
+ }
+
+ /* 4x8 movnti loop */
+ while (size >= 32) {
+ asm("movq (%0), %%r8\n"
+ "movq 8(%0), %%r9\n"
+ "movq 16(%0), %%r10\n"
+ "movq 24(%0), %%r11\n"
+ "movnti %%r8, (%1)\n"
+ "movnti %%r9, 8(%1)\n"
+ "movnti %%r10, 16(%1)\n"
+ "movnti %%r11, 24(%1)\n"
+ :: "r" (source), "r" (dest)
+ : "memory", "r8", "r9", "r10", "r11");
+ dest += 32;
+ source += 32;
+ size -= 32;
+ }
+
+ /* 1x8 movnti loop */
+ while (size >= 8) {
+ asm("movq (%0), %%r8\n"
+ "movnti %%r8, (%1)\n"
+ :: "r" (source), "r" (dest)
+ : "memory", "r8");
+ dest += 8;
+ source += 8;
+ size -= 8;
+ }
+
+ /* 1x4 movnti loop */
+ while (size >= 4) {
+ asm("movl (%0), %%r8d\n"
+ "movnti %%r8d, (%1)\n"
+ :: "r" (source), "r" (dest)
+ : "memory", "r8");
+ dest += 4;
+ source += 4;
+ size -= 4;
+ }
+
+ /* cache copy for remaining bytes */
+ if (size) {
+ memcpy((void *) dest, (void *) source, size);
+ clean_cache_range((void *) dest, size);
+ }
+}
+EXPORT_SYMBOL_GPL(memcpy_flushcache);
+
+void memcpy_page_flushcache(char *to, struct page *page, size_t offset,
+ size_t len)
+{
+ char *from = kmap_atomic(page);
+
+ memcpy_flushcache(to, from + offset, len);
+ kunmap_atomic(from);
+}
+#endif