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Message-ID: <56d85c70-80f6-aa73-ab10-20474244c7d7@igalia.com>
Date:   Fri, 30 Sep 2022 09:39:10 -0300
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Subject: Re: [REGRESSION][PATCH] Revert "pstore: migrate to crypto acomp
 interface"
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To:     Kees Cook <keescook@chromium.org>, Ard Biesheuvel <ardb@kernel.org>
Cc:     linux-kernel@vger.kernel.org, regressions@lists.linux.dev,
        linux-fsdevel@vger.kernel.org, kernel-dev@igalia.com,
        kernel@gpiccoli.net, Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Thorsten Leemhuis <linux@leemhuis.info>
References: <20220929215515.276486-1-gpiccoli@igalia.com>
 <202209291951.134BE2409@keescook>
From:   "Guilherme G. Piccoli" <gpiccoli@igalia.com>
In-Reply-To: <202209291951.134BE2409@keescook>
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On 30/09/2022 00:29, Kees Cook wrote:
> [...]
> 
> Hi!
> 
> Thanks for looking at this. I wasn't able to reproduce the problem,
> initially. Booting with pstore.backend=ramoops pstore.compress=zstd and
> writing to /dev/pmsg0, after a reboot I'm able to read it back.
> 

Hi Kees, thanks a lot for your attention!
IIUC, compression applies to dmesg only, correct?


> [...] 
> What's your setup for this? I'm using emulated NVDIMM through qemu for
> a ramoops backend. But trying this with the EFI backend (booting
> undef EFI with pstore.backend=efi), I _do_ see the problem. That's
> weird... I suspect there's some back interaction with buffer size
> differences between ramoops and EFI & deflate and zstd.
> 
> And I can confirm EFI+zstd with the acomp change reverted fixes it.
> 

I'm using qemu but was able to use real HW (Steam Deck). In both cases,
kernel is not using the entire RAM ("mem=" parameter, for example) so we
can use a bit for ramoops. Also, both setups are UEFI, hence I can also
use efi_pstore.


> [...] 
> Hm, it's possible this was just sent directly to me? If that's true, I
> apologize for not re-posting it to lkml. I suspect I didn't notice at
> the time that it wasn't CCed to a list.

No need for apologies, thanks for the clarification! How about if we add
a mailing list in the pstore entry on MAINTAINERS file, since it's just
composed for you and 3 other people now? I mean, "officially" speaking,
it should be enough to send a patch for the 4 maintainers with no list
in CC, and that's bad for achieving purposes. What list should be the
best, fsdevel? Lkml?


> 
> No worries! Whatever the case, there's always -stable updates. :)

Heheh you're right! But for something like this (pstore/dmesg
compression broke for the most backends), I'd be glad if we could fix it
before the release.
Cheers,


Guilherme