linux-kernel - Re: CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is broken, was Re: [RFC PATCH 0/6] Deep talk about folio vmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250407085943.GA27481@lst.de>
Date: Mon, 7 Apr 2025 10:59:44 +0200
From: Christoph Hellwig <hch@....de>
To: Muchun Song <muchun.song@...ux.dev>
Cc: Huan Yang <link@...o.com>, bingbu.cao@...ux.intel.com,
	Christoph Hellwig <hch@....de>,
	Matthew Wilcox <willy@...radead.org>,
	Gerd Hoffmann <kraxel@...hat.com>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>, Shuah Khan <shuah@...nel.org>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
	linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
	opensource.kernel@...o.com
Subject: Re: CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is broken, was Re: [RFC
 PATCH 0/6] Deep talk about folio vmap

On Mon, Apr 07, 2025 at 02:43:20PM +0800, Muchun Song wrote:
> By the way, in case you truly struggle to comprehend the fundamental
> aspects of HVO, I would like to summarize for you the user-visible
> behaviors in comparison to the situation where HVO is disabled.
> 
> HVO Status		Tail Page Structures	Head Page Structures
> Enabled			Read-Only (RO)		Read-Write (RW)
> Disabled		Read-Write (RW)		Read-Write (RW)
> 
> The sole distinction between the two scenarios lies in whether the
> tail page structures are allowed to be written or not. Please refrain
> from getting bogged down in the details of the implementation of HVO.

This feels extremely fragile to me.  I doubt many people know what
operations needs read vs write access to tail pages.  Or for higher
level operations if needs access to tail pages at all.