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David Hildenbrand fa2e71a6fc sparc/mm: don't unconditionally set HW writable bit when setting PTE dirty on 64bit 
On sparc64, there is no HW modified bit, therefore, SW tracks via a SW bit
if the PTE is dirty via pte_mkdirty().  However, pte_mkdirty() currently
also unconditionally sets the HW writable bit, which is wrong.

pte_mkdirty() is not supposed to make a PTE actually writable, unless the
SW writable bit -- pte_write() -- indicates that the PTE is not
write-protected.  Fortunately, sparc64 also defines a SW writable bit.

For example, this already turned into a problem in the context of THP
splitting as documented in commit 624a2c94f5 ("Partly revert "mm/thp:
carry over dirty bit when thp splits on pmd""), and for page migration, as
documented in commit 96a9c287e2 ("mm/migrate: fix wrongly apply write
bit after mkdirty on sparc64").

Also, we might want to use the dirty PTE bit in the context of KSM with
shared zeropage [1], whereby setting the page writable would be
problematic.

But more general, any code that might end up setting a PTE/PMD dirty
inside a VM without write permissions is possibly broken,

Before this commit (sun4u in QEMU):
	root@debian:~/linux/tools/testing/selftests/mm# ./mkdirty
	# [INFO] detected THP size: 8192 KiB
	TAP version 13
	1..6
	# [INFO] PTRACE write access
	not ok 1 SIGSEGV generated, page not modified
	# [INFO] PTRACE write access to THP
	not ok 2 SIGSEGV generated, page not modified
	# [INFO] Page migration
	ok 3 SIGSEGV generated, page not modified
	# [INFO] Page migration of THP
	ok 4 SIGSEGV generated, page not modified
	# [INFO] PTE-mapping a THP
	ok 5 SIGSEGV generated, page not modified
	# [INFO] UFFDIO_COPY
	not ok 6 SIGSEGV generated, page not modified
	Bail out! 3 out of 6 tests failed
	# Totals: pass:3 fail:3 xfail:0 xpass:0 skip:0 error:0

Test #3,#4,#5 pass ever since we added some MM workarounds, the
underlying issue remains.

Let's fix the remaining issues and prepare for reverting the workarounds
by setting the HW writable bit only if both, the SW dirty bit and the SW
writable bit are set.

We have to move pte_dirty() and pte_write() up. The code patching
mechanism and handling constants > 22bit is a bit special on sparc64.

The ASM logic in pte_mkdirty() and pte_mkwrite() match the logic in
pte_mkold() to create the mask depending on the machine type. The ASM
logic in __pte_mkhwwrite() matches the logic in pte_present(), just
using an "or" instead of an "and" instruction.

With this commit (sun4u in QEMU):
	root@debian:~/linux/tools/testing/selftests/mm# ./mkdirty
	# [INFO] detected THP size: 8192 KiB
	TAP version 13
	1..6
	# [INFO] PTRACE write access
	ok 1 SIGSEGV generated, page not modified
	# [INFO] PTRACE write access to THP
	ok 2 SIGSEGV generated, page not modified
	# [INFO] Page migration
	ok 3 SIGSEGV generated, page not modified
	# [INFO] Page migration of THP
	ok 4 SIGSEGV generated, page not modified
	# [INFO] PTE-mapping a THP
	ok 5 SIGSEGV generated, page not modified
	# [INFO] UFFDIO_COPY
	ok 6 SIGSEGV generated, page not modified
	# Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0

This handling seems to have been in place forever.

[1] https://lkml.kernel.org/r/533a7c3d-3a48-b16b-b421-6e8386e0b142@redhat.com

Link: https://lkml.kernel.org/r/20230411142512.438404-4-david@redhat.com
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
History 2023-04-18 16:30:00 -07:00
arch sparc/mm: don't unconditionally set HW writable bit when setting PTE dirty on 64bit 2023-04-18 16:30:00 -07:00
block block: remove obsolete config BLOCK_COMPAT 2023-03-16 09:35:44 -06:00
certs Kbuild updates for v6.3 2023-02-26 11:53:25 -08:00
crypto asymmetric_keys: log on fatal failures in PE/pkcs7 2023-03-21 16:23:56 +00:00
Documentation sync mm-stable with mm-hotfixes-stable to pick up depended-upon upstream changes 2023-04-16 12:31:58 -07:00
drivers zram: return errors from read_from_bdev_sync 2023-04-18 16:30:00 -07:00
fs smaps: fix defined but not used smaps_shmem_walk_ops 2023-04-18 16:29:54 -07:00
include userfaultfd: convert mfill_atomic() to use a folio 2023-04-18 16:29:55 -07:00
init init,mm: fold late call to page_ext_init() to page_alloc_init_late() 2023-04-05 19:42:54 -07:00
io_uring block-6.3-2023-03-24 2023-03-24 14:10:39 -07:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel prctl: add PR_GET_AUXV to copy auxv to userspace 2023-04-18 16:29:53 -07:00
lib maple_tree: use correct variable type in sizeof 2023-04-18 16:29:56 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm: backing-dev: set variables dev_attr_min,max_bytes storage-class-specifier to static 2023-04-18 16:29:56 -07:00
net mm, treewide: redefine MAX_ORDER sanely 2023-04-05 19:42:46 -07:00
rust Rust fixes for 6.3-rc1 2023-03-03 14:51:15 -08:00
samples kmemleak-test: fix kmemleak_test.c build logic 2023-04-18 16:29:47 -07:00
scripts kasan: remove hwasan-kernel-mem-intrinsic-prefix=1 for clang-14 2023-04-18 16:29:43 -07:00
security mm, treewide: redefine MAX_ORDER sanely 2023-04-05 19:42:46 -07:00
sound ALSA: hda/ca0132: fixup buffer overrun at tuning_ctl_set() 2023-03-14 17:04:53 +01:00
tools selftests/mm: mkdirty: test behavior of (pte|pmd)_mkdirty on VMAs without write permissions 2023-04-18 16:30:00 -07:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM/riscv changes for 6.3 2023-02-15 12:33:28 -05:00
.clang-format cpumask: re-introduce constant-sized cpumask optimizations 2023-03-05 14:30:34 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for *.dtso files 2023-02-26 15:28:23 +09:00
.gitignore kbuild: rpm-pkg: move source components to rpmbuild/SOURCES 2023-03-16 22:45:56 +09:00
.mailmap mailmap: update jtoppins' entry to reference correct email 2023-04-16 10:41:25 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS There is no particular theme here - mainly quick hits all over the tree. 2023-02-23 17:55:40 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: extend memblock entry to include MM initialization 2023-04-05 19:42:55 -07:00
Makefile Linux 6.3-rc4 2023-03-26 14:40:20 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.