linux-kernel - RE: [PATCH v2 3/8] x86/mm: Remove "static" from vmap_pages

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]

Date:   Mon, 27 Nov 2023 01:06:06 +0000
From:   Michael Kelley <mhklinux@...look.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "decui@...rosoft.com" <decui@...rosoft.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "urezki@...il.com" <urezki@...il.com>,
        "lstoakes@...il.com" <lstoakes@...il.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "ardb@...nel.org" <ardb@...nel.org>,
        "jroedel@...e.de" <jroedel@...e.de>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: RE: [PATCH v2 3/8] x86/mm: Remove "static" from vmap_pages_range()

From: Christoph Hellwig <hch@...radead.org> Sent: Wednesday, November 22, 2023 11:32 PM
> 
> On Thu, Nov 23, 2023 at 12:24:49AM +0000, Michael Kelley wrote:
> > > I really do not want to expose vmap_pages_range.  Please try to come up
> > > with a good way to encapsulate your map at a certain address primitive
> > > and implement it in vmalloc.c.
> >
> > To clarify, is your concern narrowly about vmap_pages_range()
> > specifically?
> 
> The prime concern is that it took a lot of effort to make
> vmap_pages_range static and remove all the abuses.  I absolutely
> object to undoing that.

OK, so I assume that means a new variant of vmap_pages_range(),
such as one that always sets the page_shift parameter to PAGE_SIZE,
is also disallowed because of the same potential for abuse.

So the only way to map a system memory page to a vmalloc
vaddr is via vmap() or some vmap() variant, which always
creates a new vmalloc area via get_vm_area().  I've done the
perf measurements, and that approach won't work for this use
case.  Independent of the alignment requirements, the churn in
creating and removing a lot of vmalloc areas has too much perf
impact.   The use case needs to create a single vmalloc area, and
then repeatedly map/unmap a page in that existing area.

I'll have to handle the top-level problem in this patch set in
a completely different way.

Michael