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 8CDCCC3DA4A for ; Tue, 20 Aug 2024 13:38:39 +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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=+1YCxIsUN9aJmfdh9L0CnvZlg1tVi+J50ik/uXoE0MM=; b=grh/j+pTw6vadwo39qpD8GXhw2 /XKNLv1zcTIbOnZQ8MW8MniQaQYqPAm0YJXbKAsnPNvBDwU/HgyrSUc5kFNg6u4gRVU1voEgTMQ+r FTOu9WZ0glGWzFxScWX7O2bCRAI8Hph3cJhgNX3RjJxNo770gn1nLE4QlRmGth3librRt4oBs4voI pxxzv7z3BDECqfPnTeV2epfgM6tfga6/pZvZC5rcrIpjGtOH5YOz7ry3/YmikxFA8JzQnHWKLa4sy JA/usesTfaM3XMC+k5+rD8H1wNHqNFBFKaTx/0tmfuQk9B5uz7dSgckZZ3SVEhSIAkmtCJMNIVKhO d4VDgfAQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sgP49-00000005Ort-2F34; Tue, 20 Aug 2024 13:38:29 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.97.1 #2 (Red Hat Linux)) id 1sgP3S-00000005Om6-0FW4 for linux-arm-kernel@lists.infradead.org; Tue, 20 Aug 2024 13:37:47 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 0D8EF60BBE; Tue, 20 Aug 2024 13:37:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A70ADC4AF0F; Tue, 20 Aug 2024 13:37:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1724161064; bh=tH4MQvrSArgIRCQkMFQYzkVHGuQSUNmjSxy71KkkWGI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=gK9oqIDobljF/2AZV2hM/1fNVm23nQgxWtsEyemtUTdE9Bm0gppOP1gYDTUsYN27z AsmKz8z1V+673LkPm0SvLeR+zW0x0seHtUONmqsVt8v1/fIu1ERSkDbukyfZEEvuEz 4NIy+VolvRYhQKixfQJVTtxCs1jIjQtYAqr9UHzSy5yxbl1WHG9dWjekdL7Jtf4X3f zeWVmR0I+os86I/XbkRd9jUbn1BN9yftXsKCVSAMsuwixkNy7+tohZ9bW/jCZqjenU kgdEOTZPMsFbQ8CI7DRjLHD02jJBlrsSIX0OZ4VQnu7jRqdozJ3PTweltxdYf/Ukz2 xltP3V2f+YGYg== Date: Tue, 20 Aug 2024 14:37:40 +0100 From: Will Deacon To: Dave Martin Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Mark Brown , Joey Gouly Subject: Re: [PATCH] arm64: signal: Update sigcontext reservations table Message-ID: <20240820133739.GA28338@willie-the-truck> References: <20240729144149.249096-1-Dave.Martin@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240729144149.249096-1-Dave.Martin@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240820_063746_258301_F1038C0F X-CRM114-Status: GOOD ( 27.96 ) 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 Mon, Jul 29, 2024 at 03:41:49PM +0100, Dave Martin wrote: > The table tracking space usage in sigcontext.__reserved[] has got > a bit out of date. > > Update it, and clarify the opt-in constraints. > > Note, svl <= 64 would be a sufficient condition for keeping the > sve_context within range when in streaming SVE mode under SME, but > then za_context gets too big and userspace loses anyway. To keep > the conditions simple, just write "svl <= 32" everywhere. > > No functional change. > > Signed-off-by: Dave Martin > > --- > > Note, this is a back-of-the-envelope calculation... but whatever way I > slice it, __reserved[] looks pretty much full (!) > > If Mark in particular can double-check the SME impact, that would be > appreciated. > > New arch features with a non-trivial amount of state that needs to be > saved may need to be disabled by default and require explicitly turning > on by a syscall unless we want to allow some ABI breakage (x86's > experience suggests that the world takes a long time to explode when > signal frames outgrow their official size, though). > > Either way, do we need a new strategy to slow down the filling of the > remaining space? There is continuing demand on it (see e.g., [1]). > > Migration note: at least glibc since version 2.34 [2] has stopped > offering compile-time constant signal stack size #defines to programs > built with -D_GNU_SOURCE. [3] This should mitigate ABI breaks for > programs that bother to size stacks correctly. > > I haven't checked what other libcs and runtimes are doing. > > Additional SME note: since userspace can freely switch in and out of > streaming SVE mode and freely enable/disable ZA and ZT0, I'm assuming > that none of sve_context, za_context and zt_context are mutually > exclusive, but please shout if I have confused myself here. > > [1] [PATCH v4 18/29] arm64: add POE signal support > https://lore.kernel.org/linux-arm-kernel/20240503130147.1154804-19-joey.gouly@arm.com/ > > [2] [glibc] glibc-2.34 > https://sourceware.org/git/?p=glibc.git;a=tag;h=9df03063320651bc629fa427eef3ac73fabb61ba > > [3] [glibc] sysconf: Add _SC_MINSIGSTKSZ/_SC_SIGSTKSZ [BZ #20305] > https://sourceware.org/git/?p=glibc.git;a=commit;f=sysdeps/unix/sysv/linux/bits/sigstksz.h;h=6c57d320484988e87e446e2e60ce42816bf51d53 > --- > arch/arm64/include/uapi/asm/sigcontext.h | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/uapi/asm/sigcontext.h b/arch/arm64/include/uapi/asm/sigcontext.h > index 8a45b7a411e0..2cd60fd64e9a 100644 > --- a/arch/arm64/include/uapi/asm/sigcontext.h > +++ b/arch/arm64/include/uapi/asm/sigcontext.h > @@ -44,11 +44,18 @@ struct sigcontext { > * > * 0x210 fpsimd_context > * 0x10 esr_context > - * 0x8a0 sve_context (vl <= 64) (optional) > + * 0x8a0 sve_context (vl <= 64 && svl <= 32) (optional) > + * 0x10 tpidr2_context (optional) > + * 0x410 za_context (svl <= 32) (optional) > + * 0x50 zt_context (optional) > + * 0x10 fpmr_context (optional) > * 0x20 extra_context (optional) > * 0x10 terminator (null _aarch64_ctx) > * > - * 0x510 (reserved for future allocation) > + * 0x90 (reserved for future allocation) > + * > + * where vl is the non-streaming SVE vector length, as set with PR_SVE_SET_VL, > + * and svl is the streaming SVE vector length, as set with PR_SME_SET_VL. These are quite fiddly to check by hand, but the ones I *did* check appear to be correct. The discussion with Mark seems tangential to the actual diff, so I'm inclined to apply this if nobody objects. Will