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074a1e1167
The virt_addr_valid() function is meant to return true iff virt_to_page() will return a valid struct page reference. This is true iff the address provided is found within the unmapped address range between PAGE_OFFSET & MAP_BASE, but we don't currently check for that condition. Instead we simply mask the address to obtain what will be a physical address if the virtual address is indeed in the desired range, shift it to form a PFN & then call pfn_valid(). This can incorrectly return true if called with a virtual address which, after masking, happens to form a physical address corresponding to a valid PFN. For example we may vmalloc an address in the kernel mapped region starting a MAP_BASE & obtain the virtual address: addr = 0xc000000000002000 When masked by virt_to_phys(), which uses __pa() & in turn CPHYSADDR(), we obtain the following (bogus) physical address: addr = 0x2000 In a common system with PHYS_OFFSET=0 this will correspond to a valid struct page which should really be accessed by virtual address PAGE_OFFSET+0x2000, causing virt_addr_valid() to incorrectly return 1 indicating that the original address corresponds to a struct page. This is equivalent to the ARM64 change made in commit |
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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.