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 E9464C4345F for ; Mon, 22 Apr 2024 17:21:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=B6KNLc64vJzEjyKBXp+dKBMHao6Y7mSIoD6IVQxz868=; b=AnvmexQEeSBGr9 e9OLKNnHw8YOHs+quGYosTdBa9hvIq0WC6ypw2K1bVPpCvmcB5n+5YPH5/P7Ss5R2x/5yibZCJh+P d0/GOKnRvHhsIqTdkHA+v7EEvA60vThlHONFCmN6IELP0xFsa6kynqrPOEFs6xI+joHFkOOqtrciM PebcR1NrHYhHGrSSWsAk7znIxiqq3LJBZNoGqr1gnizDiATH+G9MCa0nkkjxkYq9jDxGwdXSb6+Dk 3Vitz0srYmmugNKcPr+Huw7D7dY90+AVMLexL0bWiSo+Ixg4u5gBbsZMcuXTOtb8B0DQQVcsqaOud fUVFq7hTOMkpqOG4wLKw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1ryxLe-0000000ET0e-0bJy; Mon, 22 Apr 2024 17:20:58 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1ryxLb-0000000ESzj-0cTi for linux-arm-kernel@lists.infradead.org; Mon, 22 Apr 2024 17:20:56 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id E5DCD339; Mon, 22 Apr 2024 10:21:19 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.21.63]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D9CDA3F7BD; Mon, 22 Apr 2024 10:20:49 -0700 (PDT) Date: Mon, 22 Apr 2024 18:20:40 +0100 From: Mark Rutland To: Arnd Bergmann Cc: Naresh Kamboju , open list , Linux ARM , lkft-triage@lists.linaro.org, Linux Regressions , Anders Roxell , Marc Zyngier , joey.gouly@arm.com, Oliver Upton Subject: Re: gcc-8: arm64/kvm/pauth.: Error: unknown architectural extension `pauth' Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240422_102055_299491_A253B2C4 X-CRM114-Status: GOOD ( 27.33 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Apr 22, 2024 at 02:11:05PM +0200, Arnd Bergmann wrote: > On Mon, Apr 22, 2024, at 11:40, Mark Rutland wrote: > > On Mon, Apr 22, 2024 at 11:25:25AM +0200, Arnd Bergmann wrote: > >> On Mon, Apr 22, 2024, at 11:13, Mark Rutland wrote: > >> > On Mon, Apr 22, 2024 at 02:04:43PM +0530, Naresh Kamboju wrote: > >> > Given the minimum supported toolchain comes with an assembler that doesn't > >> > necessarily support ARMv8.3, I reckon we'll either have to make NV pauth > >> > support depend upon AS_HAS_ARMV8_3, or manually assemble the PACGA instruction. > >> > > >> > I suspect the latter is the better option. > >> > >> The .config linked from the report shows > >> > >> CONFIG_AS_VERSION=23101 > >> CONFIG_ARM64_PTR_AUTH_KERNEL=y > >> CONFIG_AS_HAS_ARMV8_3=y > >> > >> So it gets detected as supporting ARMv8.3. Is this the wrong > >> conditional to check, or does it get misdetected for an unsupported > >> assembler? > > > > I suspect that means the 'pauth' arch extension was added after armv8.3 > > support, and the assembler supports `-march=armv8.3-a` but does not support > > `.arch_extension pauth`. So for this code, it'd be wrong to check for > > AS_HAS_ARMV8_3, unless we used `.march armv8.3-a`, but even then that'd still > > mean configurations where we couldn't support this code. > > > > I reckon manually assembing the PACGA is the best thing to do; that sidesteps > > the need for either `.arch_extension pauth` or `.march armv8.3-a`, and aligns > > with what we do for CONFIG_ARM64_PTR_AUTH=y generally. > > > > Elsewhere in the kernel where we check for CONFIG_AS_HAS_ARMV8_3, we rely on > > ARM64_ASM_PREAMBLE containing `.arch armv8.3-a` or a later version that implies > > the presence of ARMv8.3-A instructions, and so pauth usage elsewhere is fine. > > I tested with the old binutils versions I have here and found > that anything that supports v8.3 also understands pacga, but > '.arch_extension pauth' only works in binutils-2.35 and higher, > presumably because it started out as a v8.3+ feature but was > later turned into an optional extension for all versions. > > Since there is a Kconfig check for armv8.3-a support already, I think > it's safe to just drop the .arch_extension pauth. That'll be safe, but it does mean that we'd need to *not* support pointer auth for nested virt when we have a toolchain for which CONFIG_AS_HAS_ARMV8_3=n, unless our minimum supported AS supports ARMv8.3. If our minimum supported AS *doesn't* support ARMv8.3, then we'd either need a new Kconfig symbol for NV_PAUTH support, or make CONFIG_ARM64_PTR_AUTH depend upon CONFIG_AS_HAS_ARMV8_3. AFAICT our options are: (a) Manually assembly PACGA (b) Change CONFIG_ARM64_PTR_AUTH to depend upon CONFIG_AS_HAS_ARMV8_3=y (c) Add and use new Kconfig symbol for NV PAUTH, dependent upon CONFIG_AS_HAS_ARMV8_3=y (d) Bump the minimum supported version of AS so that we can depend upon ARMv8.3 support, and just open-code the ".arch armv8.3-a" in the NV pauth code. ... and maybe some variations on that. Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel