Re: [REGRESSION] x86/hugetlb: AMD F15h VA alignment offset breaks MAP_HUGETLB alignment

[Dave Hansen]

On 5/27/26 11:28, Oscar Salvador (SUSE) wrote:
>   	if (filp) {
>   		info.align_mask = get_align_mask(filp);
>  -		info.align_offset += get_align_bits();
>  +		/*
>  +		 * Hugepages must remain hugepage-aligned, so skip adding an offset
>  +		 * in case we enabled 'align_va_addr'.
>  +		 */
>  +		if (!is_file_hugepages(filp))
>  +			info.align_offset += get_align_bits();
>   	}

That's a good hack to show the scope of the problem.

But I'd really rather this be dealt with in the arch-independent code,
not by adding hugetlb hacks to arch code. It isn't even clear to me what
exactly goes wrong when you set a tiny ->align_offset and have a larger
->align_mask. Shouldn't the tiny offset just get masked off?

        gap += (info->align_offset - gap) & info->align_mask;

I spent a whole five seconds looking at it, but something seems to be
missing from the problem description.