linux-kernel - Re: [RFC PATCH 0/2] Switch ARM to generic find

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: <Y1GpP+aY0o40MTNS@yury-laptop>
Date:   Thu, 20 Oct 2022 13:02:07 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexey Klimov <klimov.linux@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Andy Whitcroft <apw@...onical.com>,
        Dennis Zhou <dennis@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [RFC PATCH 0/2] Switch ARM to generic find_bit() API

On Thu, Oct 20, 2022 at 05:51:34PM +0100, Russell King (Oracle) wrote:
> On Wed, Oct 19, 2022 at 08:20:22PM -0700, Yury Norov wrote:
> > Hi Russell, all,
> > 
> > I'd like to respin a patch that switches ARM to generic find_bit()
> > functions.
> > 
> > Generic code works on par with arch or better, according to my
> > testing [1], and with recent improvements merged in v6.1, it should
> > be even faster.
> > 
> > ARM already uses many generic find_bit() functions - those that it
> > doesn't implement. So we are talking about migrating a subset of the
> > API; most of find_bit() family has only generic implementation on ARM.
> > 
> > The only concern about this migration is that ARM code supports
> > byte-aligned bitmap addresses, while generic code is optimized for
> > word-aligned bitmaps.
> > 
> > In my practice, I've never seen unaligned bitmaps. But to check that on
> > ARM, I added a run-time check for bitmap alignment. I gave it run on
> > several architectures and found nothing.
> > 
> > Can you please check that on your hardware and compare performance of
> > generic vs arch code for you? If everything is OK, I suggest switching
> > ARM to generic find_bit() completely.
> > 
> > Thanks,
> > Yury
> > 
> > [1] https://lore.kernel.org/all/YuWk3titnOiQACzC@yury-laptop/
> 
> I _really_ don't want to play around with this stuff right now... 6.0
> appears to have a regression on arm32 early on during boot:
> 
> [    1.410115] EXT4-fs error (device sda1): htree_dirblock_to_tree:1093: inode #256: block 8797: comm systemd: bad entry in directory: rec_len % 4 != 0 - offset=0, inode=33188, rec_len=35097, size=4096 fake=0
> 
> Booting 5.19 with the same filesystem works without issue and without
> even a fsck, but booting 6.0 always results in some problem that
> prevents it booting.
> 
> Debugging this is not easy, because there also seems to be something
> up with the bloody serial console - sometimes I get nothing, other
> times I get nothing more than:
> 
> [    2.929502] EXT4-fs error (de
> 
> and then the output stops. Is the console no longer synchronous? If it
> isn't, that's a huge mistake which can be seen right here with the
> partial message output... so I also need to work out how to make the
> console output synchronous again.

Got it.

I you think that EXT4 problems are due to unaligned bitmaps, you can take
1st patch from this series to check.

Thanks,
Yury