linux.git/mm/filemap.c, branch v6.7-rc2

mm: more ptep_get() conversion

2023-11-15T23:30:09+00:00

Commit c33c794828f2 ("mm: ptep_get() conversion") converted all (non-arch)
call sites to use ptep_get() instead of doing a direct dereference of the
pte.  Full rationale can be found in that commit's log.

Since then, three new call sites have snuck in, which directly dereference
the pte, so let's fix those up.

Unfortunately there is no reliable automated mechanism to catch these; I'm
relying on a combination of Coccinelle (which throws up a lot of false
positives) and some compiler magic to force a compiler error on
dereference (While this approach finds dereferences, it also yields a
non-booting kernel so can't be committed).

Link: https://lkml.kernel.org/r/20231114154945.490401-1-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts 
Cc: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton

mm: drop the assumption that VM_SHARED always implies writable

2023-10-18T21:34:19+00:00

Patch series "permit write-sealed memfd read-only shared mappings", v4.

The man page for fcntl() describing memfd file seals states the following
about F_SEAL_WRITE:-

    Furthermore, trying to create new shared, writable memory-mappings via
    mmap(2) will also fail with EPERM.

With emphasis on 'writable'.  In turns out in fact that currently the
kernel simply disallows all new shared memory mappings for a memfd with
F_SEAL_WRITE applied, rendering this documentation inaccurate.

This matters because users are therefore unable to obtain a shared mapping
to a memfd after write sealing altogether, which limits their usefulness. 
This was reported in the discussion thread [1] originating from a bug
report [2].

This is a product of both using the struct address_space->i_mmap_writable
atomic counter to determine whether writing may be permitted, and the
kernel adjusting this counter when any VM_SHARED mapping is performed and
more generally implicitly assuming VM_SHARED implies writable.

It seems sensible that we should only update this mapping if VM_MAYWRITE
is specified, i.e.  whether it is possible that this mapping could at any
point be written to.

If we do so then all we need to do to permit write seals to function as
documented is to clear VM_MAYWRITE when mapping read-only.  It turns out
this functionality already exists for F_SEAL_FUTURE_WRITE - we can
therefore simply adapt this logic to do the same for F_SEAL_WRITE.

We then hit a chicken and egg situation in mmap_region() where the check
for VM_MAYWRITE occurs before we are able to clear this flag.  To work
around this, perform this check after we invoke call_mmap(), with careful
consideration of error paths.

Thanks to Andy Lutomirski for the suggestion!

[1]:https://lore.kernel.org/all/20230324133646.16101dfa666f253c4715d965@linux-foundation.org/
[2]:https://bugzilla.kernel.org/show_bug.cgi?id=217238


This patch (of 3):

There is a general assumption that VMAs with the VM_SHARED flag set are
writable.  If the VM_MAYWRITE flag is not set, then this is simply not the
case.

Update those checks which affect the struct address_space->i_mmap_writable
field to explicitly test for this by introducing
[vma_]is_shared_maywrite() helper functions.

This remains entirely conservative, as the lack of VM_MAYWRITE guarantees
that the VMA cannot be written to.

Link: https://lkml.kernel.org/r/cover.1697116581.git.lstoakes@gmail.com
Link: https://lkml.kernel.org/r/d978aefefa83ec42d18dfa964ad180dbcde34795.1697116581.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes 
Suggested-by: Andy Lutomirski 
Reviewed-by: Jan Kara 
Cc: Alexander Viro 
Cc: Christian Brauner 
Cc: Hugh Dickins 
Cc: Matthew Wilcox (Oracle) 
Cc: Mike Kravetz 
Cc: Muchun Song 
Signed-off-by: Andrew Morton

filemap: remove use of wait bookmarks

2023-10-18T21:34:18+00:00

The original problem of the overly long list of waiters on a locked page
was solved properly by commit 9a1ea439b16b ("mm:
put_and_wait_on_page_locked() while page is migrated").  In the meantime,
using bookmarks for the writeback bit can cause livelocks, so we need to
stop using them.

Link: https://lkml.kernel.org/r/20231010035829.544242-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Cc: Bin Lai 
Cc: Benjamin Segall 
Cc: Daniel Bristot de Oliveira 
Cc: Dietmar Eggemann 
Cc: Ingo Molnar 
Cc: Juri Lelli 
Cc: Matthew Wilcox (Oracle) 
Cc: Mel Gorman 
Cc: Peter Zijlstra 
Cc: Steven Rostedt (Google) 
Cc: Valentin Schneider 
Cc: Vincent Guittot 

Cc: Ingo Molnar 
Signed-off-by: Andrew Morton

memcontrol: only transfer the memcg data for migration

2023-10-18T21:34:17+00:00

For most migration use cases, only transfer the memcg data from the old
folio to the new folio, and clear the old folio's memcg data.  No charging
and uncharging will be done.

This shaves off some work on the migration path, and avoids the temporary
double charging of a folio during its migration.

The only exception is replace_page_cache_folio(), which will use the old
mem_cgroup_migrate() (now renamed to mem_cgroup_replace_folio).  In that
context, the isolation of the old page isn't quite as thorough as with
migration, so we cannot use our new implementation directly.

This patch is the result of the following discussion on the new hugetlb
memcg accounting behavior:

https://lore.kernel.org/lkml/20231003171329.GB314430@monkey/

Link: https://lkml.kernel.org/r/20231006184629.155543-3-nphamcs@gmail.com
Signed-off-by: Nhat Pham 
Suggested-by: Johannes Weiner 
Acked-by: Johannes Weiner 
Cc: Frank van der Linden 
Cc: Michal Hocko 
Cc: Mike Kravetz 
Cc: Muchun Song 
Cc: Rik van Riel 
Cc: Roman Gushchin 
Cc: Shakeel Butt 
Cc: Shuah Khan 
Cc: Tejun heo 
Cc: Yosry Ahmed 
Cc: Zefan Li 
Signed-off-by: Andrew Morton

mm: use folio_xor_flags_has_waiters() in folio_end_writeback()

2023-10-18T21:34:17+00:00

Match how folio_unlock() works by combining the test for PG_waiters with
the clearing of PG_writeback.  This should have a small performance win,
and removes the last user of folio_wake().

Link: https://lkml.kernel.org/r/20231004165317.1061855-18-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Cc: Albert Ou 
Cc: Alexander Gordeev 
Cc: Andreas Dilger 
Cc: Christian Borntraeger 
Cc: Christophe Leroy 
Cc: Geert Uytterhoeven 
Cc: Heiko Carstens 
Cc: Ivan Kokshaysky 
Cc: Matt Turner 
Cc: Michael Ellerman 
Cc: Nicholas Piggin 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Richard Henderson 
Cc: Sven Schnelle 
Cc: "Theodore Ts'o" 
Cc: Thomas Bogendoerfer 
Cc: Vasily Gorbik 
Signed-off-by: Andrew Morton

mm: make __end_folio_writeback() return void

2023-10-18T21:34:17+00:00

Rather than check the result of test-and-clear, just check that we have
the writeback bit set at the start.  This wouldn't catch every case, but
it's good enough (and enables the next patch).

Link: https://lkml.kernel.org/r/20231004165317.1061855-17-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Cc: Albert Ou 
Cc: Alexander Gordeev 
Cc: Andreas Dilger 
Cc: Christian Borntraeger 
Cc: Christophe Leroy 
Cc: Geert Uytterhoeven 
Cc: Heiko Carstens 
Cc: Ivan Kokshaysky 
Cc: Matt Turner 
Cc: Michael Ellerman 
Cc: Nicholas Piggin 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Richard Henderson 
Cc: Sven Schnelle 
Cc: "Theodore Ts'o" 
Cc: Thomas Bogendoerfer 
Cc: Vasily Gorbik 
Signed-off-by: Andrew Morton

mm: add folio_xor_flags_has_waiters()

2023-10-18T21:34:17+00:00

Optimise folio_end_read() by setting the uptodate bit at the same time we
clear the unlock bit.  This saves at least one memory barrier and one
write-after-write hazard.

Link: https://lkml.kernel.org/r/20231004165317.1061855-16-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Cc: Albert Ou 
Cc: Alexander Gordeev 
Cc: Andreas Dilger 
Cc: Christian Borntraeger 
Cc: Christophe Leroy 
Cc: Geert Uytterhoeven 
Cc: Heiko Carstens 
Cc: Ivan Kokshaysky 
Cc: Matt Turner 
Cc: Michael Ellerman 
Cc: Nicholas Piggin 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Richard Henderson 
Cc: Sven Schnelle 
Cc: "Theodore Ts'o" 
Cc: Thomas Bogendoerfer 
Cc: Vasily Gorbik 
Signed-off-by: Andrew Morton

mm: delete checks for xor_unlock_is_negative_byte()

2023-10-18T21:34:17+00:00

Architectures which don't define their own use the one in
asm-generic/bitops/lock.h.  Get rid of all the ifdefs around "maybe we
don't have it".

Link: https://lkml.kernel.org/r/20231004165317.1061855-15-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Acked-by: Geert Uytterhoeven 
Cc: Albert Ou 
Cc: Alexander Gordeev 
Cc: Andreas Dilger 
Cc: Christian Borntraeger 
Cc: Christophe Leroy 
Cc: Heiko Carstens 
Cc: Ivan Kokshaysky 
Cc: Matt Turner 
Cc: Michael Ellerman 
Cc: Nicholas Piggin 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Richard Henderson 
Cc: Sven Schnelle 
Cc: "Theodore Ts'o" 
Cc: Thomas Bogendoerfer 
Cc: Vasily Gorbik 
Signed-off-by: Andrew Morton

bitops: add xor_unlock_is_negative_byte()

2023-10-18T21:34:16+00:00

Replace clear_bit_and_unlock_is_negative_byte() with
xor_unlock_is_negative_byte().  We have a few places that like to lock a
folio, set a flag and unlock it again.  Allow for the possibility of
combining the latter two operations for efficiency.  We are guaranteed
that the caller holds the lock, so it is safe to unlock it with the xor. 
The caller must guarantee that nobody else will set the flag without
holding the lock; it is not safe to do this with the PG_dirty flag, for
example.

Link: https://lkml.kernel.org/r/20231004165317.1061855-8-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Cc: Albert Ou 
Cc: Alexander Gordeev 
Cc: Andreas Dilger 
Cc: Christian Borntraeger 
Cc: Christophe Leroy 
Cc: Geert Uytterhoeven 
Cc: Heiko Carstens 
Cc: Ivan Kokshaysky 
Cc: Matt Turner 
Cc: Michael Ellerman 
Cc: Nicholas Piggin 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Richard Henderson 
Cc: Sven Schnelle 
Cc: "Theodore Ts'o" 
Cc: Thomas Bogendoerfer 
Cc: Vasily Gorbik 
Signed-off-by: Andrew Morton

mm: add folio_end_read()

2023-10-18T21:34:16+00:00

Provide a function for filesystems to call when they have finished reading
an entire folio.

Link: https://lkml.kernel.org/r/20231004165317.1061855-4-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Cc: Albert Ou 
Cc: Alexander Gordeev 
Cc: Andreas Dilger 
Cc: Christian Borntraeger 
Cc: Christophe Leroy 
Cc: Geert Uytterhoeven 
Cc: Heiko Carstens 
Cc: Ivan Kokshaysky 
Cc: Matt Turner 
Cc: Michael Ellerman 
Cc: Nicholas Piggin 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Richard Henderson 
Cc: Sven Schnelle 
Cc: "Theodore Ts'o" 
Cc: Thomas Bogendoerfer 
Cc: Vasily Gorbik 
Signed-off-by: Andrew Morton