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Date:   Wed, 28 Jun 2023 10:10:55 -0700
In-Reply-To: <2023062832-barrier-strenuous-9499@gregkh>
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Message-ID: <20230628171055.1312737-1-yuxiaozhang@google.com>
Subject: Re: Re: [PATCH] pstore: ramoops: support pmsg size larger than
 kmalloc limitation
From:   Yuxiao Zhang <yuxiaozhang@google.com>
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     Kees Cook <keescook@chromium.org>, Tony Luck <tony.luck@intel.com>,
        "'Guilherme G . Piccoli'" <gpiccoli@igalia.com>,
        linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
        wak@google.com
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Thanks for reviewing the patch.

On 28 Jun 2023 07:30:16 +0200, Greg KH wrote:
>What is that max size?

The max size is arch dependent, it should be 2^(PAGE_SIZE+MAX_ORDER). In our environment it is 4M.

>what in-kernel user is hitting this in the pstore implementation?

We are trying to use pmsg to hold a core dump file, so we have pmsg-size=32M and thus hit this issue.

Other than us, here is one I found that trying to save dmesg beyond kmalloc limitaton:
https://lore.kernel.org/lkml/b2d66d9f-15a6-415c-2485-44649027a1d5@igalia.com/T/

Thanks,
-Yuxiao Zhang