Commit 6c77676645 ("iov_iter: Fix iter_xarray_get_pages{,_alloc}()")
introduced a problem on some 32-bit architectures (at least arm, xtensa,
csky,sparc and mips), that have a 'size_t' that is 'unsigned int'.
The reason is that we now do
min(nr * PAGE_SIZE - offset, maxsize);
where 'nr' and 'offset' and both 'unsigned int', and PAGE_SIZE is
'unsigned long'. As a result, the normal C type rules means that the
first argument to 'min()' ends up being 'unsigned long'.
In contrast, 'maxsize' is of type 'size_t'.
Now, 'size_t' and 'unsigned long' are always the same physical type in
the kernel, so you'd think this doesn't matter, and from an actual
arithmetic standpoint it doesn't.
But on 32-bit architectures 'size_t' is commonly 'unsigned int', even if
it could also be 'unsigned long'. In that situation, both are unsigned
32-bit types, but they are not the *same* type.
And as a result 'min()' will complain about the distinct types (ignore
the "pointer types" part of the error message: that's an artifact of the
way we have made 'min()' check types for being the same):
lib/iov_iter.c: In function 'iter_xarray_get_pages':
include/linux/minmax.h:20:35: error: comparison of distinct pointer types lacks a cast [-Werror]
20 | (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
| ^~
lib/iov_iter.c:1464:16: note: in expansion of macro 'min'
1464 | return min(nr * PAGE_SIZE - offset, maxsize);
| ^~~
This was not visible on 64-bit architectures (where we always define
'size_t' to be 'unsigned long').
Force these cases to use 'min_t(size_t, x, y)' to make the type explicit
and avoid the issue.
[ Nit-picky note: technically 'size_t' doesn't have to match 'unsigned
long' arithmetically. We've certainly historically seen environments
with 16-bit address spaces and 32-bit 'unsigned long'.
Similarly, even in 64-bit modern environments, 'size_t' could be its
own type distinct from 'unsigned long', even if it were arithmetically
identical.
So the above type commentary is only really descriptive of the kernel
environment, not some kind of universal truth for the kinds of wild
and crazy situations that are allowed by the C standard ]
Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Link: https://lore.kernel.org/all/YqRyL2sIqQNDfky2@debian/
Cc: Jeff Layton <jlayton@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The maths at the end of iter_xarray_get_pages() to calculate the actual
size doesn't work under some circumstances, such as when it's been asked to
extract a partial single page. Various terms of the equation cancel out
and you end up with actual == offset. The same issue exists in
iter_xarray_get_pages_alloc().
Fix these to just use min() to select the lesser amount from between the
amount of page content transcribed into the buffer, minus the offset, and
the size limit specified.
This doesn't appear to have caused a problem yet upstream because network
filesystems aren't getting the pages from an xarray iterator, but rather
passing it directly to the socket, which just iterates over it. Cachefiles
*does* do DIO from one to/from ext4/xfs/btrfs/etc. but it always asks for
whole pages to be written or read.
Fixes: 7ff5062079 ("iov_iter: Add ITER_XARRAY")
Reported-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Alexander Viro <viro@zeniv.linux.org.uk>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Mike Marshall <hubcap@omnibond.com>
cc: Gao Xiang <xiang@kernel.org>
cc: linux-afs@lists.infradead.org
cc: v9fs-developer@lists.sourceforge.net
cc: devel@lists.orangefs.org
cc: linux-erofs@lists.ozlabs.org
cc: linux-cachefs@redhat.com
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
The functions copy_page_to_iter_pipe() and push_pipe() can both
allocate a new pipe_buffer, but the "flags" member initializer is
missing.
Fixes: 241699cd72 ("new iov_iter flavour: pipe-backed")
To: Alexander Viro <viro@zeniv.linux.org.uk>
To: linux-fsdevel@vger.kernel.org
To: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Take advantage of how kmap_local_folio() works to simplify the loop.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Introduce a new nofault flag to indicate to iov_iter_get_pages not to
fault in user pages.
This is implemented by passing the FOLL_NOFAULT flag to get_user_pages,
which causes get_user_pages to fail when it would otherwise fault in a
page. We'll use the ->nofault flag to prevent iomap_dio_rw from faulting
in pages when page faults are not allowed.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Introduce a new fault_in_iov_iter_writeable helper for safely faulting
in an iterator for writing. Uses get_user_pages() to fault in the pages
without actually writing to them, which would be destructive.
We'll use fault_in_iov_iter_writeable in gfs2 once we've determined that
the iterator passed to .read_iter isn't in memory.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Turn iov_iter_fault_in_readable into a function that returns the number
of bytes not faulted in, similar to copy_to_user, instead of returning a
non-zero value when any of the requested pages couldn't be faulted in.
This supports the existing users that require all pages to be faulted in
as well as new users that are happy if any pages can be faulted in.
Rename iov_iter_fault_in_readable to fault_in_iov_iter_readable to make
sure this change doesn't silently break things.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Turn fault_in_pages_{readable,writeable} into versions that return the
number of bytes not faulted in, similar to copy_to_user, instead of
returning a non-zero value when any of the requested pages couldn't be
faulted in. This supports the existing users that require all pages to
be faulted in as well as new users that are happy if any pages can be
faulted in.
Rename the functions to fault_in_{readable,writeable} to make sure
this change doesn't silently break things.
Neither of these functions is entirely trivial and it doesn't seem
useful to inline them, so move them to mm/gup.c.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Both iov_iter_get_pages and iov_iter_get_pages_alloc return the number
of bytes of the iovec they could get the pages for. When they cannot
get any pages, they're supposed to return 0, but when the start of the
iovec isn't page aligned, the calculation goes wrong and they return a
negative value. Fix both functions.
In addition, change iov_iter_get_pages_alloc to return NULL in that case
to prevent resource leaks.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
In an ideal world, when someone is passed an iov_iter and returns X bytes,
then X bytes would have been consumed/advanced from the iov_iter. But we
have use cases that always consume the entire iterator, a few examples
of that are iomap and bdev O_DIRECT. This means we cannot rely on the
state of the iov_iter once we've called ->read_iter() or ->write_iter().
This would be easier if we didn't always have to deal with truncate of
the iov_iter, as rewinding would be trivial without that. We recently
added a commit to track the truncate state, but that grew the iov_iter
by 8 bytes and wasn't the best solution.
Implement a helper to save enough of the iov_iter state to sanely restore
it after we've called the read/write iterator helpers. This currently
only works for IOVEC/BVEC/KVEC as that's all we need, support for other
iterator types are left as an exercise for the reader.
Link: https://lore.kernel.org/linux-fsdevel/CAHk-=wiacKV4Gh-MYjteU0LwNBSGpWrK-Ov25HdqB1ewinrFPg@mail.gmail.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Fix all kernel-doc warnings in lib/iov_iter.c:
lib/iov_iter.c:695: warning: Function parameter or member 'i' not described in '_copy_mc_to_iter'
lib/iov_iter.c:695: warning: Excess function parameter 'iter' description in '_copy_mc_to_iter'
lib/iov_iter.c:695: warning: No description found for return value of '_copy_mc_to_iter'
lib/iov_iter.c:758: warning: Function parameter or member 'i' not described in '_copy_from_iter_flushcache'
lib/iov_iter.c:758: warning: Excess function parameter 'iter' description in '_copy_from_iter_flushcache'
lib/iov_iter.c:758: warning: No description found for return value of '_copy_from_iter_flushcache'
Link: https://lkml.kernel.org/r/20210809051053.6531-1-rdunlap@infradead.org
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This warning was there to catch any architectures that still use
CONFIG_SET_FS, and that would mis-use iov_iter_init() for anything that
wasn't a proper user space pointer. So that
WARN_ON_ONCE(uaccess_kernel());
makes perfect conceptual sense: you really shouldn't use a kernel
pointer with set_fs(KERNEL_DS) and then pass it to iov_iter_init().
HOWEVER.
Guenter Roeck reports that this warning actually triggers in no-mmu
configurations of both ARM and m68k. And the reason isn't that they
pass in a kernel pointer under set_fs(KERNEL_DS) at all: the reason is
that in those configurations, "uaccess_kernel()" is simply not reliable.
Those no-mmu setups set USER_DS and KERNEL_DS to the same values, so you
can't test for the difference.
In particular, the no-mmu case for ARM does
#define USER_DS KERNEL_DS
#define uaccess_kernel() (true)
so USER_DS and KERNEL_DS have the same value, and uaccess_kernel() is
always trivially true.
The m68k case is slightly different and not quite as obvious. It does
(spread out over multiple header files just to be extra exciting:
asm/processor.h, asm/segment.h and asm-generic/uaccess.h):
#define TASK_SIZE (0xFFFFFFFFUL)
#define USER_DS MAKE_MM_SEG(TASK_SIZE)
#define KERNEL_DS MAKE_MM_SEG(~0UL)
#define get_fs() (current_thread_info()->addr_limit)
#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
but the end result is the same: uaccess_kernel() will always be true,
because USER_DS and KERNEL_DS end up having the same value, even if that
value is defined differently.
This is very arguably a misfeature in those implementations, but in the
end we don't really care. All modern architectures have gotten rid of
set_fs() already, and generic kernel code never uses it. And while the
sanity check was a nice idea, an architecture would have to go the extra
mile to actually break this.
So this well-intentioned warning isn't really all that likely to find
anything but these known false positives, and as such just isn't worth
maintaining.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Fixes: 8cd54c1c84 ("iov_iter: separate direction from flavour")
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1) kmap_atomic() is not needed here, kmap_local_page() is enough.
2) No need to make sum = csum_block_add(sum, next, off); conditional
upon next != 0 - adding 0 is a no-op as far as csum_block_add()
is concerned.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
kmap_local_page() is enough there. Moreover, we can use _copy_to_iter()
for actual copying in those cases - no useful extra checks on the
address we are copying from in that call.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
recalculating offset on each iteration is pointless - on all subsequent
passes through the loop it will be zero anyway.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Iterator macros used to provide the arguments for step callbacks in
a structure matching the flavour - iovec for ITER_IOVEC, kvec for
ITER_KVEC and bio_vec for ITER_BVEC. That already broke down for
ITER_XARRAY (bio_vec there); now that we are using kvec callback
for bvec and xarray cases, we are always passing a pointer + length
(void __user * + size_t for ITER_IOVEC callback, void * + size_t
for everything else).
Note that the original reason for bio_vec (page + offset + len) in
case of ITER_BVEC used to be that we did *not* want to kmap a
page when all we wanted was e.g. to find the alignment of its
subrange. Now all such users are gone and the ones that are left
want the page mapped anyway for actually copying the data.
So in all cases we have pointer + length, and there's no good
reason for keeping those in struct iovec or struct kvec - we
can just pass them to callback separately.
Again, less boilerplate in callbacks...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Making iterator macros keep track of the amount of data copied is pretty
easy and it has several benefits:
1) we no longer need the mess like (from += v.iov_len) - v.iov_len
in the callbacks - initial value + total amount copied so far would do
just fine.
2) less obviously, we no longer need to remember the initial amount
of data we wanted to copy; the loops in iterator macros are along the lines
of
wanted = bytes;
while (bytes) {
copy some
bytes -= copied
if short copy
break
}
bytes = wanted - bytes;
Replacement is
offs = 0;
while (bytes) {
copy some
offs += copied
bytes -= copied
if short copy
break
}
bytes = offs;
That wouldn't be a win per se, but unlike the initial value of bytes, the amount
copied so far *is* useful in callbacks.
3) in some cases (csum_and_copy_..._iter()) we already had offs manually
maintained by the callbacks. With that change we can drop that.
Less boilerplate and more readable code...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
After the previous commit we have
* xarray and bvec callbacks idential in all cases
* both equivalent to kvec callback wrapped into
kmap_local_page()/kunmap_local() pair.
So we can pass only two (iovec and kvec) callbacks to
iterate_and_advance() and let iterate_{bvec,xarray} wrap
it into kmap_local_page()/kunmap_local_page().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... and now we finally can sort out the mess in _copy_mc_to_iter().
Provide a variant of iterate_and_advance() that does *NOT* ignore
the return values of bvec, xarray and kvec callbacks, use that in
_copy_mc_to_iter(). That gets rid of magic in those callbacks -
we used to need it so we'd get at least the right return value in
case of failure halfway through.
As a bonus, now iterator is advanced by the amount actually copied
for all flavours. That's what the callers expect and it used to do that
correctly in iovec and xarray cases. However, in kvec and bvec cases
the iterator had not been advanced on such failures, breaking the users.
Fixed now...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... incidentally, using pointer instead of index in an array
(the only change here) trims half-kilobyte of .text...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
The differences between iterate_iovec and iterate_kvec are minor:
* kvec callback is treated as if it returned 0
* initialization of __p is with i->iov and i->kvec resp.
which is trivially dealt with.
No code generation changes - compiler is quite capable of turning
left = ((void)(STEP), 0);
__v.iov_len -= left;
(with no accesses to left downstream) and
(void)(STEP);
into the same code.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Premature optimization is the root of all evil... Trying
to unroll the first pass through the loop makes it harder
to follow and not just for readers - compiler ends up
generating worse code than it would on a "non-optimized"
loop.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
iov_iter_advance() needs to do some non-trivial work when it's given
0 as argument (skip all empty iovecs, mostly). We used to implement
it via iterate_and_advance(); we no longer do so and for all other
users of iterate_and_advance() zero length is a no-op.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Namely, have off counted starting from 0 rather than from csstate->off.
To compensate we need to shift the initial value (csstate->sum) (rotate
by 8 bits, as usual for csum) and do the same after we are finished adding
the pieces up.
What we get out of that is a bit more redundancy in our variables - from
is always equal to addr + off, which will be useful several commits down
the road.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Replacement is called copy_page_from_iter_atomic(); unlike the old primitive the
callers do *not* need to do iov_iter_advance() after it. In case when they end
up consuming less than they'd been given they need to do iov_iter_revert() on
everything they had not consumed. That, however, needs to be done only on slow
paths.
All in-tree callers converted. And that kills the last user of iterate_all_kinds()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
note that in bvec case pages can be compound ones - we can't just assume
that each segment is covered by one (sub)page
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Here iterate_all_kinds() is used just to find the first (non-empty, in
case of iovec) segment. Which can be easily done explicitly.
Note that in bvec case we now can get more than PAGE_SIZE worth of them,
in case when we have a compound page in bvec and a range that crosses
a subpage boundary. Older behaviour had been to stop on that boundary;
we used to get the right first page (for_each_bvec() took care of that),
but that was all we'd got.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
For one thing, it's only used for iovec (and makes sense only for those).
For another, here we don't care about iov_offset, since the beginning of
the first segment and the end of the last one are ignored. So it makes
a lot more sense to just walk through the iovec array...
We need to deal with the case of truncated iov_iter, but unlike the
situation with iov_iter_alignment() we don't care where the last
segment ends - just which segment is the last one.
[fixed a braino spotted by Qian Cai <quic_qiancai@quicinc.com>]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
It's easier to go over the array manually. We need to watch out
for truncated iov_iter, though - iovec array might cover more
than i->count.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
1) constify iov_iter argument; we are not advancing it in this primitive.
2) cap the amount requested by the amount of data in iov_iter. All
existing callers should've been safe, but the check is really cheap and
doing it here makes for easier analysis, as well as more consistent
semantics among the primitives.
3) don't bother with iterate_iovec(). Explicit loop is not any harder
to follow, and we get rid of standalone iterate_iovec() users - it's
only used by iterate_and_advance() and (soon to be gone) iterate_all_kinds().
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
We can do better than generic iterate_and_advance() for this one;
inspired by bvec_iter_advance() (and massaged into that form by
equivalent transformations).
[fixed a braino caught by kernel test robot <oliver.sang@intel.com>]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Instead of having them mixed in iter->type, use separate ->iter_type
and ->data_source (u8 and bool resp.) And don't bother with (pseudo-)
bitmap for the former - microoptimizations from being able to check
if the flavour is one of two values are not worth the confusion for
optimizer. It can't prove that we never get e.g. ITER_IOVEC | ITER_PIPE,
so we end up with extra headache.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
iovec is the most common one; test it first and test explicitly,
rather than "not anything else". Replace all flavour checks with
use of iov_iter_is_...() helpers.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Use corresponding plain variants, revert on short copy. That's the way it
should've been done from the very beginning, except that we didn't have
iov_iter_revert() back then...
[fixed another braino caught by Qian Cai <quic_qiancai@quicinc.com>]
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
asking to advance by more than we have left in the iov_iter should
move to the very end; it should *not* leave negative i->count and
it should not spew into syslog, etc. - it's a legitimate operation.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
... and actually should just check it's given an iovec-backed iterator
in the first place.
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
In situation when copy_page_to_iter() got a compound page the current
code would only work on systems with no CONFIG_HIGHMEM. It *is* the majority
of real-world setups, or we would've drown in bug reports by now. Still needs
fixing.
Current variant works for solitary page; rename that to
__copy_page_to_iter() and turn the handling of compound pages into a loop over
subpages.
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Remove iov_iter_for_each_range() as it's no longer used with the removal of
lustre.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Patch series "btrfs: Convert kmap/memset/kunmap to memzero_user()".
Lifting memzero_user(), convert it to kmap_local_page() and then use it
in btrfs.
This patch (of 3):
memzero_page() can replace the kmap/memset/kunmap pattern in other
places in the code. While zero_user() has the same interface it is not
the same call and its use should be limited and some of those calls may
be better converted from zero_user() to memzero_page().[1] But that is
not addressed in this series.
Lift memzero_page() to highmem.
[1] https://lore.kernel.org/lkml/CAHk-=wijdojzo56FzYqE5TOYw2Vws7ik3LEMGj9SPQaJJ+Z73Q@mail.gmail.com/
Link: https://lkml.kernel.org/r/20210309212137.2610186-1-ira.weiny@intel.com
Link: https://lkml.kernel.org/r/20210309212137.2610186-2-ira.weiny@intel.com
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: David Sterba <dsterba@suse.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Fix four things[1] in the patch that adds ITER_XARRAY[2]:
(1) Remove the address_space struct predeclaration. This is a holdover
from when it was ITER_MAPPING.
(2) Fix _copy_mc_to_iter() so that the xarray segment updates count and
iov_offset in the iterator before returning.
(3) Fix iov_iter_alignment() to not loop in the xarray case. Because the
middle pages are all whole pages, only the end pages need be
considered - and this can be reduced to just looking at the start
position in the xarray and the iteration size.
(4) Fix iov_iter_advance() to limit the size of the advance to no more
than the remaining iteration size.
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Jeff Layton <jlayton@redhat.com>
Tested-by: Dave Wysochanski <dwysocha@redhat.com>
Link: https://lore.kernel.org/r/YIVrJT8GwLI0Wlgx@zeniv-ca.linux.org.uk [1]
Link: https://lore.kernel.org/r/161918448151.3145707.11541538916600921083.stgit@warthog.procyon.org.uk [2]
Pull kmap conversion updates from David Sterba:
"This contains changes regarding kmap API use and eg conversion from
kmap_atomic to kmap_local_page.
The API belongs to memory management but to save cross-tree
dependency headaches we've agreed to take it through the btrfs tree
because there are some trivial conversions possible, while the rest
will need some time and getting the easy cases out of the way would be
convenient.
The changes can be grouped:
- function exports, new helpers
- new VM_BUG_ON for additional verification; it's been discussed if
it should be VM_BUG_ON or BUG_ON, the former was chosen due to
performance reasons
- code replaced by relevant helpers"
[ This is an updated version of a request that originally came in during
the merge window, but I asked for some updates:
https://lore.kernel.org/lkml/cover.1614090658.git.dsterba@suse.com/
which is why this got merge after the merge window closed. - Linus ]
* 'kmap-conversion-for-5.12' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux:
btrfs: use copy_highpage() instead of 2 kmaps()
btrfs: use memcpy_[to|from]_page() and kmap_local_page()
mm/highmem: Add VM_BUG_ON() to mem*_page() calls
mm/highmem: Introduce memcpy_page(), memmove_page(), and memset_page()
mm/highmem: Convert memcpy_[to|from]_page() to kmap_local_page()
mm/highmem: Lift memcpy_[to|from]_page to core
