From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.skyhub.de ([5.9.137.197]:58780 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727541AbgDAJdQ (ORCPT ); Wed, 1 Apr 2020 05:33:16 -0400 Date: Wed, 1 Apr 2020 11:33:10 +0200 From: Borislav Petkov Subject: Re: [PATCH v4 6/8] x86: bump ZO_z_extra_bytes margin for zstd Message-ID: <20200401093310.GA13748@zn.tnic> References: <20200401053913.216783-1-nickrterrell@gmail.com> <20200401053913.216783-7-nickrterrell@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200401053913.216783-7-nickrterrell@gmail.com> Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Nick Terrell Cc: Nick Terrell , linux-kernel@vger.kernel.org, Chris Mason , linux-kbuild@vger.kernel.org, x86@kernel.org, gregkh@linuxfoundation.org, Petr Malat , Kees Cook , Kernel Team , Adam Borowski , Patrick Williams , rmikey@fb.com, mingo@kernel.org, Patrick Williams , Sedat Dilek On Tue, Mar 31, 2020 at 10:39:11PM -0700, Nick Terrell wrote: > From: Nick Terrell > > Bump the ZO_z_extra_bytes margin for zstd. > > Zstd needs 3 bytes per 128 KB, and has a 22 byte fixed overhead. > Zstd needs to maintain 128 KB of space at all times, since that is > the maximum block size. See the comments regarding in-place > decompression added in lib/decompress_unzstd.c for details. > > Reviewed-by: Kees Cook > Tested-by: Sedat Dilek > Signed-off-by: Nick Terrell > --- > arch/x86/boot/header.S | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S > index 97d9b6d6c1af..b820875c5c95 100644 > --- a/arch/x86/boot/header.S > +++ b/arch/x86/boot/header.S > @@ -536,8 +536,14 @@ pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr > # the size-dependent part now grows so fast. > # > # extra_bytes = (uncompressed_size >> 8) + 65536 > +# > +# ZSTD compressed data grows by at most 3 bytes per 128K, and only has a 22 > +# byte fixed overhead but has a maximum block size of 128K, so it needs a > +# larger margin. > +# > +# extra_bytes = (uncompressed_size >> 8) + 131072 > > -#define ZO_z_extra_bytes ((ZO_z_output_len >> 8) + 65536) > +#define ZO_z_extra_bytes ((ZO_z_output_len >> 8) + 131072) > #if ZO_z_output_len > ZO_z_input_len > # define ZO_z_extract_offset (ZO_z_output_len + ZO_z_extra_bytes - \ > ZO_z_input_len) > -- So why is this change unconditional if only this compression alg. needs it? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette