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Peter Anvin" Subject: Re: [REGRESSION] x86/hugetlb: AMD F15h VA alignment offset breaks MAP_HUGETLB alignment Message-ID: References: <20260527143643.GO31091@soohrt.org> <5f70e840-9d0e-4cef-8574-b355cf26e0c4@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5f70e840-9d0e-4cef-8574-b355cf26e0c4@intel.com> X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: AAF91100009 X-Stat-Signature: 7z48wasew4ghum84ey7cbyu1w4gjky6o X-Rspam-User: X-HE-Tag: 1779947131-210961 X-HE-Meta: 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 EYBP/lH+ PHrAT2zvwuOYjM+jTNgytdHZk+xUGQXiqsQf06nHJRPUzIvgLERkgAhAUIskFDSkxcq7MBSEppzvgXkREK8L4McqtGCeOtHzssx48oQIYJanvDQrxlXydaolnwXwTJRfaOd4nBxWSEL3IGB4EAviUUwjecJ/uRg6ccqicG9bWJnaVHfk3VqeBz+6MBzqB3V8UZdd4/OBclR+aCWcwppfYXocBkBYoXZwQ7sTPZT2WjQT3GZSHszgCngcF4LBPkkwaZsKA Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 27, 2026 at 02:04:10PM -0700, Dave Hansen wrote: > 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. Haha, do not worry, I myself have 0 interestin spreading hugetlb-specific code around (on the contrary), but I wanted to proof the point. > > 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 would assume so, but something is definitely going in with the calculation, as I could reproduce this if I artificially set align_offset to 0x1000 for hugetlb mappings. I will find some time today to have a deep look. -- Oscar Salvador SUSE Labs