From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 51C05C5DF85 for ; Thu, 20 Aug 2026 13:52:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:Subject:References:In-Reply-To:Message-Id:Cc:To:From:Date: MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=zD3zgeevoRIzapGsmdBgzD2O1ClYtdB1PLKQWNbkPKo=; b=d+ouOEDP5rTlGTVDesVsVXrEdk 9LOaVkcpAIsJSmplRMeowlUux5j+sPdLFmqvcirUSikC9kSzazBQZle9pYZXDsvJfsoYE7zMTS3AF bWI9QHPuP0wOujkhOKbuWcUT22Cd/RMDupAsOi0t1D/Xfbhm3hqEBFB3BKAJxbKKFdK9aMyupbhdf 7tMFyzypM2/uSwH8IpIuc72NdpE4gE6K3TphEIQCte5zcJQBcsUbicvDQmSQbKHFhuS717FU42AhE aLlJfPC7lEM0emHsuaCbjyj/I7Zuw1gqlouRQlQLDYKxKmv8RaSnPptYoxQuBTL3dbdd6jjg/DUyp NFEcLxqw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wx3Bm-0000000Bdly-0b7k; Thu, 20 Aug 2026 13:52:14 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wx3Bl-0000000Bdlr-0pKs for linux-arm-kernel@lists.infradead.org; Thu, 20 Aug 2026 13:52:13 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 91C2F43F51; Thu, 20 Aug 2026 13:52:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CB83B1F00A3E; Thu, 20 Aug 2026 13:52:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787233932; bh=zD3zgeevoRIzapGsmdBgzD2O1ClYtdB1PLKQWNbkPKo=; h=Date:From:To:Cc:In-Reply-To:References:Subject; b=V6zQLFSjbRumG/ZzB3vbDdpuLLbThnUSpsktcBfLVAyMvdcHJSH3GxKAsjeEBg/8D LPiYec1o16YRv8a6lP0W5MzGA5ef7hgPfSPcggKG9TvBUooDvUAIfJ2OgFjQkwRar7 u568h8PtyZ+7NIfcXHGNTp/ZGVXskBBIfNIpqzWAQ1vEImO0n4ZNki4JQWGfMrUwWv dZmXbbA1TtzNucXDrOV1saOmDMR4aYelK4W4V13CBuc/lCROY+DhzuzFRWxrji2/7J W+wGGPYzeI0tVTeC/0p9sWL7Tgz5MaA7wB9n9bE8kxUHZTiG4Ld266BaznqKuHrB5I DWHJxA1jmp6cw== Received: from ams-compute-02.internal (ams-compute-02.internal [10.64.2.62]) by mailfauth.ams.internal (Postfix) with ESMTP id 5B3491980052; Thu, 20 Aug 2026 09:52:10 -0400 (EDT) Received: from ams-imap-11 ([10.64.2.31]) by ams-compute-02.internal (MEProxy); Thu, 20 Aug 2026 09:52:10 -0400 X-ME-Sender: X-ME-Proxy-Cause: dmFkZTFCRl0HBk9vYQsxdiFgcQZaSulDIVtSv1i9/4ktEgUTQZk1cXT59PNxolqKjaIURt PrlEIP3DvEkM/OsJiqg/2TmQx1W6mg2nqzi+xe+QbVO2C0pfaxDDdU8nxtnlX400v+r679 +KSbEyoZ2CTHCsw3vaT+xD2R0btGAzbTpAIC8cyDlHyfu3oci4nNrH1yx/C4Ez8VbyJPCU tK+ZfABSogjQ+YVETYj/lNczXQp60Nl3uG5mGPk3Ae7mMpvK5rXHJ7J304V98Un46T+NVz wLsplI4V3Pmet6WCRV5l/xTyAFOtP0DKC7nS8IEPYH1yLgHWde0j2/rXJO63BdkpiZmcOP TjiKlq7ZT/2FFHDwKSMNno1497GnyXB7fpuSA5XN6eEZAnFpOIQTx7mmi2Ut2c/sJyH1ni au/UV0iLua0EDuMjnpqTNeT5EhE0Aw2RrElW7LbAF8PDkKOUq2iTj/g6TMbOIDdfMjZdQq HlMWeqNAfrRUoV/kYDR32EJjcyU4kEn3x0Z3+nS6zRVQPHiwAx51yn/LH8qUAeNSNzHt3s wG37OoOThOJ2J5Vbt+5r107mVwxdVR0KVjNYNSqIiQpC9REEdN/blPHwk/UNopQGTzTd+K iEAULIYJvRG19JFxMNFMvPOPtA6hbkkhCetchodaE+8955qua/+GDetp3Qtg X-ME-Proxy: Feedback-ID: ice86485a:Fastmail Received: by mailuser.ams.internal (Postfix, from userid 501) id 50AE8F80071; Thu, 20 Aug 2026 09:52:07 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface MIME-Version: 1.0 Date: Thu, 20 Aug 2026 16:50:41 +0300 From: "Ard Biesheuvel" To: "Will Deacon" Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, "Arnd Bergmann" , "Eric Biggers" , "Daniel Borkmann" , "Catalin Marinas" , "Alexei Starovoitov" , "Oliver Upton" , "Herbert Xu" , "Marc Zyngier" Message-Id: <207397b0-07f2-467c-8419-3109a506cc7d@app.fastmail.com> In-Reply-To: References: <20260811140132.22778-1-will@kernel.org> <20260811140132.22778-7-will@kernel.org> <03208978-a825-4ae5-b47e-3dd6133ecbf0@app.fastmail.com> Subject: Re: [PATCH 06/12] arm64: assembler: Remove endianness helper macros Content-Type: text/plain Content-Transfer-Encoding: 7bit X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, 20 Aug 2026, at 16:45, Will Deacon wrote: > On Thu, Aug 20, 2026 at 04:27:06PM +0300, Ard Biesheuvel wrote: >> >> On Thu, 20 Aug 2026, at 16:19, Will Deacon wrote: >> > On Sun, Aug 16, 2026 at 10:42:40AM +0100, Will Deacon wrote: >> >> On Tue, Aug 11, 2026 at 05:04:43PM +0200, Ard Biesheuvel wrote: >> >> > On Tue, 11 Aug 2026, at 16:01, Will Deacon wrote: >> >> > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S >> >> > > index 87a822e5c4ca..8951ce693552 100644 >> >> > > --- a/arch/arm64/kernel/head.S >> >> > > +++ b/arch/arm64/kernel/head.S >> >> > > @@ -138,8 +138,7 @@ SYM_CODE_START_LOCAL(record_mmu_state) >> >> > > b.ne 0f >> >> > > mrs x19, sctlr_el2 >> >> > > 0: >> >> > > -CPU_LE( tbnz x19, #SCTLR_ELx_EE_SHIFT, 1f ) >> >> > > -CPU_BE( tbz x19, #SCTLR_ELx_EE_SHIFT, 1f ) >> >> > > + tbnz x19, #SCTLR_ELx_EE_SHIFT, 1f >> >> > > tst x19, #SCTLR_ELx_C // Z := (C == 0) >> >> > > and x19, x19, #SCTLR_ELx_M // isolate M bit >> >> > > csel x19, xzr, x19, eq // clear x19 if Z >> >> > >> >> > There is some more code that can be removed here - see >> >> > 2ced0f30a426c7301350681f838344d5aea711e3 >> >> >> >> Good spot, thanks! I'll do some more surgery at -rc1. >> > >> > Looking at this again, I'm not sure we can remove much here. I think we >> > probably still want to force little-endian (i.e. clear the EE bit) if >> > we're entered as big-endian. I've changed the following EOR to a BIC >> > (see below), but I think that's about all we can do? >> > >> >> Well, the only case where we allow an active ID map is when doing EFI >> boot, which is guaranteed to be little-endian. Since the kernel is now >> also guaranteed to be little-endian, we should be able to simply kick >> the CPU in LE mode right at the start, no? And simply ignore the case >> of a BE bootloader entering with the MMU and caches enabled? > > Hmm, so why did we support this in the first place given that EFI is > guaranteed to be little-endian? Or was that just because we wanted to > handle the case of a big-endian kernel being loaded by EFI? > The original report is here: https://lore.kernel.org/linux-arm-kernel/Y9FZsBEu8hSVVIA8@dev-arch.thelio-3990X/ So it would probably have been sufficient at the time to just kick the CPU into LE mode - I don't remember why I added the additional logic tbh.