linux-kernel - Re: [PATCH] mm, vmalloc: use __GFP

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: <20170307150845.075cceea71647bfeba3c5e22@linux-foundation.org>
Date:   Tue, 7 Mar 2017 15:08:45 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        Cristopher Lameter <cl@...ux.com>, <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm, vmalloc: use __GFP_HIGHMEM implicitly

On Tue,  7 Mar 2017 15:10:20 +0100 Michal Hocko <mhocko@...nel.org> wrote:

> __vmalloc* allows users to provide gfp flags for the underlying
> allocation. This API is quite popular
> $ git grep "=[[:space:]]__vmalloc\|return[[:space:]]*__vmalloc" | wc -l
> 77
> 
> the only problem is that many people are not aware that they really want
> to give __GFP_HIGHMEM along with other flags because there is really no
> reason to consume precious lowmemory on CONFIG_HIGHMEM systems for pages
> which are mapped to the kernel vmalloc space. About half of users don't
> use this flag, though. This signals that we make the API unnecessarily
> too complex.
> 
> This patch simply uses __GFP_HIGHMEM implicitly when allocating pages to
> be mapped to the vmalloc space. Current users which add __GFP_HIGHMEM
> are simplified and drop the flag.

hm.  What happens if a caller wants only lowmem pages?  Drivers do
weird stuff...