linux-kernel - Re: [PATCH] module/decompress: Never use kunmap() for local un-mappings

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Message-ID: <e30b31c9-9b18-80a3-8ff0-97b958ab0b8f@cachyos.org>
Date:   Tue, 21 Mar 2023 09:23:07 +0100
From:   Piotr Gorski <piotrgorski@...hyos.org>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Chris Down <chris@...isdown.name>,
        Nick Terrell <terrelln@...com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-modules@...r.kernel.org,
        linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
        live-patching@...r.kernel.org, bpf@...r.kernel.org,
        llvm@...ts.linux.dev
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH] module/decompress: Never use kunmap() for local
 un-mappings

Reviewed-by: Piotr Gorski <piotrgorski@...hyos.org>

W dniu 15.03.2023 o 13:52, Fabio M. De Francesco pisze:
> Use kunmap_local() to unmap pages locally mapped with kmap_local_page().
>
> kunmap_local() must be called on the kernel virtual address returned by
> kmap_local_page(), differently from how we use kunmap() which instead
> expects the mapped page as its argument.
>
> In module_zstd_decompress() we currently map with kmap_local_page() and
> unmap with kunmap(). This breaks the code and so it should be fixed.
>
> Cc: Piotr Gorski <piotrgorski@...hyos.org>
> Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>
> Cc: Luis Chamberlain <mcgrof@...nel.org>
> Cc: Stephen Boyd <swboyd@...omium.org>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Fixes: 169a58ad824d ("module/decompress: Support zstd in-kernel decompression")
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
>   kernel/module/decompress.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/module/decompress.c b/kernel/module/decompress.c
> index bb79ac1a6d8f..7ddc87bee274 100644
> --- a/kernel/module/decompress.c
> +++ b/kernel/module/decompress.c
> @@ -267,7 +267,7 @@ static ssize_t module_zstd_decompress(struct load_info *info,
>   		zstd_dec.size = PAGE_SIZE;
>   
>   		ret = zstd_decompress_stream(dstream, &zstd_dec, &zstd_buf);
> -		kunmap(page);
> +		kunmap_local(zstd_dec.dst);
>   		retval = zstd_get_error_code(ret);
>   		if (retval)
>   			break;