On Thu, Feb 06, 2025 at 03:27:43PM +0200, Mike Rapoport wrote: >From: Alexander Graf <graf@xxxxxxxxxx> > >With KHO (Kexec HandOver), we need a way to ensure that the new kernel >does not allocate memory on top of any memory regions that the previous >kernel was handing over. But to know where those are, we need to include >them in the memblock.reserved array which may not be big enough to hold >all ranges that need to be persisted across kexec. To resize the array, >we need to allocate memory. That brings us into a catch 22 situation. > >The solution to that is limit memblock allocations to the scratch regions: >safe regions to operate in the case when there is memory that should remain >intact across kexec. > >KHO provides several "scratch regions" as part of its metadata. These >scratch regions are contiguous memory blocks that known not to contain any >memory that should be persisted across kexec. These regions should be large >enough to accommodate all memblock allocations done by the kexeced kernel. > >We introduce a new memblock_set_scratch_only() function that allows KHO to memblock_set_kho_scratch_only? >indicate that any memblock allocation must happen from the scratch regions. > >Later, we may want to perform another KHO kexec. For that, we reuse the >same scratch regions. To ensure that no eventually handed over data gets >allocated inside a scratch region, we flip the semantics of the scratch >region with memblock_clear_scratch_only(): After that call, no allocations memblock_clear_kho_scratch_only? >may happen from scratch memblock regions. We will lift that restriction >in the next patch. > -- Wei Yang Help you, Help me
