[PATCH v4 12/14] x86: Add KHO support

[Wei Yang]

On Mon, Feb 24, 2025 at 04:36:38PM +0200, Mike Rapoport wrote:
>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 <graf at 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.
> 

Thanks, I see you point. We would add memory region during kho_populate() and
mark it scratch.

>> 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.

-- 
Wei Yang
Help you, Help me