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 WZh53eTD 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+0100, Ryan Roberts wrote: >> The kernel linear mapping is painted in very early stage of system boot. >> The cpufeature has not been finalized yet at this point. So the linear >> mapping is determined by the capability of boot CPU only. If the boot >> CPU supports BBML2, large block mappings will be used for linear >> mapping. >> >> But the secondary CPUs may not support BBML2, so repaint the linear >> mapping if large block mapping is used and the secondary CPUs don't >> support BBML2 once cpufeature is finalized on all CPUs. >> >> If the boot CPU doesn't support BBML2 or the secondary CPUs have the >> same BBML2 capability with the boot CPU, repainting the linear mapping >> is not needed. >> >> Repainting is implemented by the boot CPU, which we know supports BBML2, >> so it is safe for the live mapping size to change for this CPU. The >> linear map region is walked using the pagewalk API and any discovered >> large leaf mappings are split to pte mappings using the existing helper >> functions. Since the repainting is performed inside of a stop_machine(), >> we must use GFP_ATOMIC to allocate the extra intermediate pgtables. But >> since we are still early in boot, it is expected that there is plenty of >> memory available so we will never need to sleep for reclaim, and so >> GFP_ATOMIC is acceptable here. >> >> The secondary CPUs are all put into a waiting area with the idmap in >> TTBR0 and reserved map in TTBR1 while this is performed since they >> cannot be allowed to observe any size changes on the live mappings. Some >> of this infrastructure is reused from the kpti case. Specifically we >> share the same flag (was __idmap_kpti_flag, now idmap_kpti_bbml2_flag) >> since it means we don't have to reserve any extra pgtable memory to >> idmap the extra flag. >> >> Co-developed-by: Yang Shi >> Signed-off-by: Yang Shi >> Signed-off-by: Ryan Roberts > I think this works, so: > > Reviewed-by: Catalin Marinas Thank you! > > However, I wonder how likely we are to find this combination in the > field to be worth carrying this code upstream. With kpti, we were aware > of platforms requiring it but is this also the case for BBM? If not, I'd > keep the patch out until we get a concrete example. At least we (Ampere) are very very unlikely to ship asymmetric systems AFAICT. Thanks, Yang >