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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 31 Aug 2021 19:19:27 +0200
Message-ID: <CAMuHMdWbSUGRGAVi-17C3hyDBZnGLAsmbAs+wXPHiCNWWLbMpA@mail.gmail.com>
Subject: Re: [PATCH] fbmem: don't allow too huge resolutions
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Daniel Vetter <daniel.vetter@ffwll.ch>,
        syzbot <syzbot+04168c8063cfdde1db5e@syzkaller.appspotmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Colin King <colin.king@canonical.com>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        syzkaller-bugs@googlegroups.com,
        Randy Dunlap <rdunlap@infradead.org>
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Hi Handa-san,

On Tue, Aug 31, 2021 at 5:24 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
> On 2021/08/31 15:48, Geert Uytterhoeven wrote:
> > Furthermore, this restricts the virtual frame buffer size on 64-bit,
> > too, while graphics cards can have much more than 4 GiB of RAM.
>
> Excuse me, but do you mean that some hardware allows allocating more than
> UINT_MAX bytes of memory for kernel frame buffer drivers?

While smem_len is u32 (there have been complaints about such
limitations on 64-bit platforms as far as 10 years ago), I see no
reason why a graphics card with more than 4 GiB of RAM would not be
able to provide a very large virtual screen.

Of course e.g. vga16fb cannot, as it is limited to 64 KiB.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds