Re: [PATCH 5/5] alloc_tag: config to store page allocation tag refs in page flags

[Matthew Wilcox]

On Mon, Aug 19, 2024 at 08:15:11AM -0700, Suren Baghdasaryan wrote:
> @@ -91,7 +97,7 @@
>  #endif
>  
>  #if ZONES_WIDTH + LRU_GEN_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + \
> -	KASAN_TAG_WIDTH + LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
> +	KASAN_TAG_WIDTH + ALLOC_TAG_REF_WIDTH + LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
>  #define LAST_CPUPID_WIDTH LAST_CPUPID_SHIFT
>  #else
>  #define LAST_CPUPID_WIDTH 0

So if ALLOC_TAG_REF_WIDTH is big enough, it's going to force last_cpupid
into struct page.  That will misalign struct page and disable HVO --
with no warning!