2c33568098
During boot, all non-reserved memblock memory is exposed to page_alloc via memblock_free_pages->__free_pages_core(). This results in kasan_free_pages() being called, which poisons that memory. Poisoning all that memory lengthens boot time. The most noticeable effect is observed with the HW_TAGS mode. A boot-time impact may potentially also affect systems with large amount of RAM. This patch changes the tag-based modes to not poison the memory during the memblock->page_alloc transition. An exception is made for KASAN_GENERIC. Since it marks all new memory as accessible, not poisoning the memory released from memblock will lead to KASAN missing invalid boot-time accesses to that memory. With KASAN_SW_TAGS, as it uses the invalid 0xFE tag as the default tag for all memory, it won't miss bad boot-time accesses even if the poisoning of memblock memory is removed. With KASAN_HW_TAGS, the default memory tags values are unspecified. Therefore, if memblock poisoning is removed, this KASAN mode will miss the mentioned type of boot-time bugs with a 1/16 probability. This is taken as an acceptable trafe-off. Internally, the poisoning is removed as follows. __free_pages_core() is used when exposing fresh memory during system boot and when onlining memory during hotplug. This patch adds a new FPI_SKIP_KASAN_POISON flag and passes it to __free_pages_ok() through free_pages_prepare() from __free_pages_core(). If FPI_SKIP_KASAN_POISON is set, kasan_free_pages() is not called. All memory allocated normally when the boot is over keeps getting poisoned as usual. Link: https://lkml.kernel.org/r/a0570dc1e3a8f39a55aa343a1fc08cd5c2d4cad6.1613692950.git.andreyknvl@google.com Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Alexander Potapenko <glider@google.com> Cc: Marco Elver <elver@google.com> Cc: Peter Collingbourne <pcc@google.com> Cc: Evgenii Stepanov <eugenis@google.com> Cc: Branislav Rankov <Branislav.Rankov@arm.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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.