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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Ard, On 08/10/2020 16:35, Ard Biesheuvel wrote: > On arm64, the global variable memstart_addr represents the physical > address of PAGE_OFFSET, and so physical to virtual translations or > vice versa used to come down to simple additions or subtractions > involving the values of PAGE_OFFSET and memstart_addr. > > When support for 52-bit virtual addressing was introduced, we had to > deal with PAGE_OFFSET potentially being outside of the region that can > be covered by the virtual range (as the 52-bit VA capable build needs > to be able to run on systems that are only 48-bit VA capable), and for > this reason, another translation was introduced, and recorded in the > global variable physvirt_offset. > > However, if we go back to the original definition of memstart_addr, > i.e., the physical address of PAGE_OFFSET, it turns out that there is > no need for two separate translations: instead, we can simply subtract > the size of the unaddressable VA space from memstart_addr to make the > available physical memory appear in the 48-bit addressable VA region. > > This simplifies things, but also fixes a bug on KASLR builds, which > may update memstart_addr later on in arm64_memblock_init(), but fails > to update vmemmap and physvirt_offset accordingly. > Apologies, I didn't spot that before. > Fixes: 5383cc6efed13 ("arm64: mm: Introduce vabits_actual") > Signed-off-by: Ard Biesheuvel Thanks for this. It is much better to modify memstart_addr rather than introducing needless complexity. Reviewed-by: Steve Capper Cheers, -- Steve _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel