Michael Ellerman <m...@ellerman.id.au> writes: > Nathan Lynch <nath...@linux.ibm.com> writes: >> Michael Ellerman <m...@ellerman.id.au> writes: >>> Nathan Lynch <nath...@linux.ibm.com> writes: >>>> Memory locations passed as arguments from the OS to RTAS usually need >>>> to be addressable in 32-bit mode and must reside in the Real Mode >>>> Area. On PAPR guests, the RMA starts at logical address 0 and is the >>>> first logical memory block reported in the LPAR’s device tree. >>>> >>>> On powerpc targets with RTAS, Linux makes available to user space a >>>> region of memory suitable for arguments to be passed to RTAS via >>>> sys_rtas(). This region (rtas_rmo_buf) is allocated via the memblock >>>> API during boot in order to ensure that it satisfies the requirements >>>> described above. >>>> >>>> With radix MMU, the upper limit supplied to the memblock allocation >>>> can exceed the bounds of the first logical memory block, since >>>> ppc64_rma_size is ULONG_MAX and RTAS_INSTANTIATE_MAX is 1GB. >>> >>> Why does the size of the first memory block matter for radix? >> >> Here is my understanding: in the platform architecture, the size of the >> first memory block equals the RMA, regardless of the MMU mode. It just >> so happens that when using radix, Linux can pass ibm,configure-connector >> a work area address outside of the RMA because the allocation >> constraints for the work area are computed differently. It would be >> wrong of the OS to pass RTAS arguments outside of this region with hash >> MMU as well. > > If that's the requirement then shouldn't we be adjusting ppc64_rma_size? > Otherwise aren't other uses of ppc64_rma_size going to run into similar > problems.
Not all allocations limited by ppc64_rma_size set up memory that is passed to RTAS though, do they? e.g. emergency_stack_init and init_fallback_flush? Those shouldn't be confined to the first LMB unnecessarily. That's why I'm thinking what I've written here should be generalized a bit and placed in an early allocator function that can be used to set up the user region and the per-cpu reentrant RTAS argument buffers (see allocate_paca_ptrs/new_rtas_args). So far those two sites are the only ones I'm convinced need attention.
