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Commit 11e63f6d authored by Dan Williams's avatar Dan Williams
Browse files

x86, pmem: fix broken __copy_user_nocache cache-bypass assumptions 



Before we rework the "pmem api" to stop abusing __copy_user_nocache()
for memcpy_to_pmem() we need to fix cases where we may strand dirty data
in the cpu cache. The problem occurs when copy_from_iter_pmem() is used
for arbitrary data transfers from userspace. There is no guarantee that
these transfers, performed by dax_iomap_actor(), will have aligned
destinations or aligned transfer lengths. Backstop the usage
__copy_user_nocache() with explicit cache management in these unaligned
cases.

Yes, copy_from_iter_pmem() is now too big for an inline, but addressing
that is saved for a later patch that moves the entirety of the "pmem
api" into the pmem driver directly.

Fixes: 5de490da ("pmem: add copy_from_iter_pmem() and clear_pmem()")
Cc: <stable@vger.kernel.org>
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: "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: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: default avatarToshi Kani <toshi.kani@hpe.com>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
parent 956a4cd2

arch/x86/include/asm/pmem.h

+31 −11
Original line number Diff line number Diff line
@@ -55,7 +55,8 @@ static inline int arch_memcpy_from_pmem(void *dst, const void *src, size_t n) 
 * @size:	number of bytes to write back

 *

 * Write back a cache range using the CLWB (cache line write back)

 * instruction.

 * instruction. Note that @size is internally rounded up to be cache

 * line size aligned.

 */

static inline void arch_wb_cache_pmem(void *addr, size_t size)

{
@@ -69,15 +70,6 @@ static inline void arch_wb_cache_pmem(void *addr, size_t size) 
		clwb(p);

}



/*

 * copy_from_iter_nocache() on x86 only uses non-temporal stores for iovec

 * iterators, so for other types (bvec & kvec) we must do a cache write-back.

 */

static inline bool __iter_needs_pmem_wb(struct iov_iter *i)

{

	return iter_is_iovec(i) == false;

}



/**

 * arch_copy_from_iter_pmem - copy data from an iterator to PMEM

 * @addr:	PMEM destination address
@@ -94,7 +86,35 @@ static inline size_t arch_copy_from_iter_pmem(void *addr, size_t bytes, 
	/* TODO: skip the write-back by always using non-temporal stores */

	len = copy_from_iter_nocache(addr, bytes, i);



	if (__iter_needs_pmem_wb(i))

	/*

	 * In the iovec case on x86_64 copy_from_iter_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.

	 *

	 * In the non-iovec case the entire destination needs to be

	 * flushed.

	 */

	if (iter_is_iovec(i)) {

		unsigned long flushed, dest = (unsigned long) addr;



		if (bytes < 8) {

			if (!IS_ALIGNED(dest, 4) || (bytes != 4))

				arch_wb_cache_pmem(addr, 1);

		} else {

			if (!IS_ALIGNED(dest, 8)) {

				dest = ALIGN(dest, boot_cpu_data.x86_clflush_size);

				arch_wb_cache_pmem(addr, 1);

			}



			flushed = dest - (unsigned long) addr;

			if (bytes > flushed && !IS_ALIGNED(bytes - flushed, 8))

				arch_wb_cache_pmem(addr + bytes - 1, 1);

		}

	} else

		arch_wb_cache_pmem(addr, bytes);



	return len;