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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Tue, 27 Jul 2021 15:18:58 +0200
Message-ID: <CAK8P3a15ykABd61Rad5iaZtGN=-+Guk0CNyCMK3XD7TgubG7hg@mail.gmail.com>
Subject: Re: [PATCH] virtio-console: avoid DMA from vmalloc area
To:     Xianting Tian <xianting.tian@linux.alibaba.com>
Cc:     Amit Shah <amit@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        gregkh <gregkh@linuxfoundation.org>,
        Omar Sandoval <osandov@fb.com>,
        "open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" 
        <virtualization@lists.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Tue, Jul 27, 2021 at 3:13 PM Xianting Tian
<xianting.tian@linux.alibaba.com> wrote:
> @@ -1127,13 +1128,18 @@ static int put_chars(u32 vtermno, const char *buf, int count)
>         if (!port)
>                 return -EPIPE;
>
> -       data = kmemdup(buf, count, GFP_ATOMIC);
> -       if (!data)
> -               return -ENOMEM;
> +       if (is_vmalloc_addr(buf)) {
> +               data = kmemdup(buf, count, GFP_ATOMIC);

What about buffers in .data? If those are in a loadable module, I guess you have
the same problem as with vmalloc() and vmap().

is_vmalloc_or_module_addr() would take care of both, not sure if there are
other examples that don't work. In theory it could be ioremap(), kmap_atomic()
or fixmap as well, but those seem less likely to matter here.

        Arnd