linux-kernel - Re: [PATCH 0/6] Boot-time switching between 4- and 5-level paging for 4.15, Part 1

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: <20171024094039.4lonzocjt5kras7m@gmail.com>
Date:   Tue, 24 Oct 2017 11:40:40 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] Boot-time switching between 4- and 5-level paging
 for 4.15, Part 1


* Kirill A. Shutemov <kirill@...temov.name> wrote:

> On Mon, Oct 23, 2017 at 02:40:14PM +0200, Ingo Molnar wrote:
> > 
> > * Kirill A. Shutemov <kirill@...temov.name> wrote:
> > 
> > > > Making a variable that 'looks' like a constant macro dynamic in a rare Kconfig 
> > > > scenario is asking for trouble.
> > > 
> > > We expect boot-time page mode switching to be enabled in kernel of next
> > > generation enterprise distros. It shoudn't be that rare.
> > 
> > My point remains even with not-so-rare Kconfig dependency.
> 
> I don't follow how introducing new variable that depends on Kconfig option
> would help with the situation.

A new, properly named variable or function (max_physmem_bits or 
max_physmem_bits()) that is not all uppercase would make it abundantly clear that 
it is not a constant but a runtime value.

> We would end up with inverse situation: people would use MAX_PHYSMEM_BITS
> where the new variable need to be used and we will in the same situation.

It should result in sub-optimal resource allocations worst-case, right?

We could also rename it to MAX_POSSIBLE_PHYSMEM_BITS to make it clear that the 
real number of bits can be lower.

Thanks,

	Ingo