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x86, pmem: fix broken __copy_user_nocache cache-bypass assumptions

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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: 5de490daec ("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: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams 2017-04-06 09:04:31 -07:00
parent 956a4cd2c9
commit 11e63f6d92
1 changed files with 31 additions and 11 deletions
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42
arch/x86/include/asm/pmem.h
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@ -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;