On Mon, Feb 24, 2025 at 07:13:55AM +0000, Wei Yang wrote: > On Thu, Feb 06, 2025 at 03:27:52PM +0200, Mike Rapoport wrote: > >From: Alexander Graf <g...@amazon.com> > [...] > >diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c > >index 82b96ed9890a..0b81cd70b02a 100644 > >--- a/arch/x86/kernel/e820.c > >+++ b/arch/x86/kernel/e820.c > >@@ -1329,6 +1329,24 @@ void __init e820__memblock_setup(void) > > memblock_add(entry->addr, entry->size); > > } > > > >+ /* > >+ * At this point with KHO we only allocate from scratch memory. > >+ * At the same time, we configure memblock to only allow > >+ * allocations from memory below ISA_END_ADDRESS which is not > >+ * a natural scratch region, because Linux ignores memory below > >+ * ISA_END_ADDRESS at runtime. Beside very few (if any) early > >+ * allocations, we must allocate real-mode trapoline below > >+ * ISA_END_ADDRESS. > >+ * > >+ * To make sure that we can actually perform allocations during > >+ * this phase, let's mark memory below ISA_END_ADDRESS as scratch > >+ * so we can allocate from there in a scratch-only world. > >+ * > >+ * After real mode trampoline is allocated, we clear scratch > >+ * marking from the memory below ISA_END_ADDRESS > >+ */ > >+ memblock_mark_kho_scratch(0, ISA_END_ADDRESS); > >+ > > At the beginning of e820__memblock_setup() we call memblock_allow_resize(), > which means during adding memory region it could double the array. And the > memory used here is from some region just added.
There are large KHO scratch areas that will be used for most allocations. Marking the memory below ISA_END_ADDRESS as KHO scratch is required to satisfy allocations that explicitly limit the allocation to ISA_END_ADDRESS, e.g the real time trampoline. > But with KHO, I am afraid it would fail? > > > /* Throw away partial pages: */ > > memblock_trim_memory(PAGE_SIZE); > > > > -- > Wei Yang > Help you, Help me -- Sincerely yours, Mike.
