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

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Date:   Wed, 15 Mar 2023 11:16:31 -0700
From:   Ira Weiny <ira.weiny@...el.com>
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:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Piotr Gorski <piotrgorski@...hyos.org>,
        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

Fabio M. De Francesco wrote:
> 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>

Reviewed-by: 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;
> -- 
> 2.39.2
>