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open-power / hostboot

System initialization firmware for Power systems
Apache License 2.0
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Can I map the memory to within 128TB #225

Closed Grubby0624 closed 1 year ago

Grubby0624 commented 1 year ago

https://github.com/open-power/hostboot/blob/07e6d7d68f0cce3fdc25848b59baf46aa3dabc5c/src/import/chips/p10/procedures/hwp/nest/p10_mss_eff_grouping.C#L4788

I want to adapt to a lower version kernel on the P10 eBMC system, The maximum physical memory capacity specified for the kernel is 128TB: https://github.com/torvalds/linux/blob/c470abd4fde40ea6a0846a2beab642a578c0b8cd/arch/powerpc/include/asm/sparsemem.h#L14 But for 4-proc machines, each group needs to occupy 64TB of memory, so the memory on Proc2/3 cannot be recognized by the kernel. Do we have the means to map the memory on Proc2/3 to within 128TB? I tried to modify the mapping by modifying the topology ID, but this method only works on iOSCM CPUs. For DCM CPUs, the modification will result in "build smp failed"

dcrowell77 commented 1 year ago

The 64TB space per topology id is a pretty fundamental piece of the architecture. I'm not aware of any way to change that.

I would recommend maybe asking over in https://github.com/open-power/skiboot since that team might be more aware of any tricks to get Linux to run.

dcrowell77 commented 1 year ago

I confirmed with the hardware team that there is no method to shrink the per-chip address space to less than 64TB.