From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9287713B7A3 for ; Tue, 27 Jan 2026 02:40:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769481631; cv=none; b=sRxJNfTZnNHFITZbLuUWMdSZQeKHOyqfS/hH6x1dmkd4z19y3+7/a2NqFXJDJiaspkI1aoBqbyOI5+fY2l4naU9CwGfB/Pcfs18T39ZAdRLEUGFO00XcJ1QnWGE/TrOY5HrLFerGoKzY+/TVD/reU6hCGVTHDd4qQl1RMhuqgfI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769481631; c=relaxed/simple; bh=ns5JBUngKf40/LpkEMIjHEtekqhIwxe1nBEewMenVRs=; h=Date:From:To:CC:Subject:In-Reply-To:References:Message-ID: MIME-Version:Content-Type; b=qo7LNp4ahJnCIAJ5Cvojfib8u79lYldxcPuxE+weRe+L6QiFjXXoDX6XfEkvFE0bZ2rwNXkSz7pyrPxHl5O6VXlcUJHU/4QsyW2ExCSh+np1OAEO0eS1uXocc/+pMlsikBfLk17k0vxfdR5SWtNXU731CeS2RfIL+z1Y3iFq6hA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=D6B9vdfM; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="D6B9vdfM" Received: from ehlo.thunderbird.net (c-76-133-66-138.hsd1.ca.comcast.net [76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 60R2duKN3383594 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 26 Jan 2026 18:39:57 -0800 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 60R2duKN3383594 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2026012301; t=1769481598; bh=ns5JBUngKf40/LpkEMIjHEtekqhIwxe1nBEewMenVRs=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=D6B9vdfMoDYzUzToi98E7dL6z4C9Ld95Tf37XinHB2exymwvUTl3tPLSZYyqHrQnS 2b8VSU1Ee5XLA8D4ny72R9C6vSo+Cii0rwYNmog3FN2L0LCCEZHabRYRDYZIV7XOMY bTzs/XcRcEyHcTNnsrzr34jyzdku6Hgu5otBNYb4RT2A9GlXGQH+B5H+xXk/c2S0jf nynubQC9xbrZejKvsMRpnZBheU5x1fBCWMH4lhAGLxSQOpdFl6IwL8tWKOXh8KOd6Y FkQcsee7D2/ZLQTa6rC4QPVsS5AqH7Jlj4L9w8TYC0LsHCadEOgjGJ0JxfY7N1lLAT CGCXVr5GEYSVQ== Date: Mon, 26 Jan 2026 18:39:50 -0800 From: "H. Peter Anvin" To: Simon Glass CC: ubizjak@gmail.com, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, bp@alien8.de, dave.hansen@linux.intel.com, kas@kernel.org, kees@kernel.org, linux-coco@lists.linux.dev, mingo@redhat.com, nathan@kernel.org, peterz@infradead.org, pmladek@suse.com, rick.p.edgecombe@intel.com, tglx@kernel.org, x86@kernel.org Subject: Re: [PATCH v1 08/14] x86: make CONFIG_EFI_STUB unconditional User-Agent: K-9 Mail for Android In-Reply-To: References: <20260122185740.50298-1-sjg@chromium.org> <90DAAB54-CBF0-47BD-981A-FEDD26CDA0FD@zytor.com> <643bfc24-8cc1-4f70-85e2-f6829c8e03db@zytor.com> Message-ID: <76997572-A728-48D1-8020-4729B34908F9@zytor.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On January 26, 2026 5:44:43 PM PST, Simon Glass wrote: >Hi Peter, > >On Tue, 27 Jan 2026 at 11:21, H=2E Peter Anvin wrote: >> >> On 2026-01-26 13:19, Simon Glass wrote: >> >> >> >> Including the EFI stub doesn't mean using EFI to boot is required=2E >> > >> > Yes, understood, but it adds bloat=2E More importantly it will lead t= o >> > people assuming that the stub is always used and thus unwittingly blu= r >> > the boundary between the stub and the kernel itself=2E >> > >> > What is the actual need for this? >> > >> >> I would argue that the opposite is more likely: someone inadvertently b= uilds a >> kernel without the stub, the bootloader goes down a legacy support path= and >> things seems to work=2E=2E=2E except for some platform subtleties=2E >> >> The bloat is there, but it is small and is only in the on-disk kernel i= mage; >> it is zero at runtime=2E >> >> As such, I don't think this option is a particularly good idea anymore= =2E If >> necessary, it could be hidden behind an EXPERT option, but I first want= ed to >> see who if anyone actually cares in a meaningful way to maintain this o= ption=2E >> Every option, after all, adds maintenance burden=2E >> >> Note that the BIOS stub is unconditionally compiled and included, and t= hat has >> not been an issue=2E > >What is the maintenance burden here? I could potentially take that on, >but I would first want to understand what is involved=2E > >The use of the word 'legacy' worries me too=2E Is this patch a step >towards removing the non-EFI path? > >Regards, >Simon Bypassing the firmware stub (BIOS or EFI) is really only appropriate for s= pecial user cases, like kexec, because it removes the ability for the kerne= l to deal with system issues at an early point=2E However, kexec needs it, and it's not going to go away=2E However, that do= esn't mean we should encourage this in cases which doesn't need it (no matt= er what the Grub maintainers tell you=2E) Now, if you are using KVM without EFI you are probably doing BIOS boot (re= gardless of if you know it or not), entering via the BIOS firmware stub=2E