Messages in this thread | | | Date | Thu, 8 Dec 2022 00:27:02 +0000 | From | Oliver Upton <> | Subject | Re: [PATCH 3/4] KVM: arm64: selftests: Align VA space allocator with TTBR0 |
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On Thu, Dec 08, 2022 at 12:18:07AM +0000, Sean Christopherson wrote:
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> Together, what about? The #ifdef is a bit gross, especially around "hi_start", > but it's less duplicate code. And IMO, having things bundled in the same place > makes it a lot easier for newbies (to arm64 or kernel coding in general) to > understand what's going on and why arm64 is different.
I'd rather we not go this route. We really shouldn't make any attempt to de-dupe something that is inherently architecture specific.
For example:
> + /* > + * All architectures supports splitting the virtual address space into > + * a high and a low half. Populate both halves, except for arm64 which > + * currently uses only TTBR0_EL1 (arbitrary selftests "logic"), i.e. > + * only has a valid low half. > + */ > + sparsebit_num_t nr_va_bits = (1ULL << (vm->va_bits - 1)) >> vm->page_shift;
This is still wrong for arm64. When we say the VA space is 48 bits, we really do mean that TTBR0 is able to address a full 48 bits. So this truncates the MSB for the addressing mode.
With the code living in the arm64 side of the shop, I can also tailor the comment to directly match the architecture to provide breadcrumbs tying it back to the Arm ARM.
-- Thanks, Oliver
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