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 86417C3DA4A for ; Mon, 29 Jul 2024 14:54:19 +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: MIME-Version:Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-Type: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=h8S2q5PK6iG2OTgRKWu/GZqdQ3p7vQvsuiQsQlsJgnE=; b=yQqSpPkBrfF3qDTt/bv+IWb3eo kzSZzhJtio0bVWmCcMZvmAZwBc9oQ/V1ibzfa+bT/k8vnWg931Elmgk72sqO1/u4Lhd6ViBV0j714 HR9oRuGS03acHUTT0gpoeYW6O2aDjOEadxcCO+nsmjSucZOFQ46GaC88+qlfkbeBhUHIcLz8XlMEo 1MaOw6vHEsmZNkQgehciaTpIMwajVTzASBlkX+Wp9dRPPGJG7CjdWSaK8T/kWHbRzmvZoJyd7Bui4 lCD4NFUSmMWcxmoDCTEsyJEAaTAbdv1IsmVew4TI4lwMs4qhA4QEgfcAVMBWDfKpQNFFxRx78iqpC B40tRNuw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.97.1 #2 (Red Hat Linux)) id 1sYRlK-0000000Bkmo-1HT2; Mon, 29 Jul 2024 14:54:10 +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 1sYRZT-0000000BgyV-1LRR for linux-arm-kernel@lists.infradead.org; Mon, 29 Jul 2024 14:41:57 +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 46ECC1007; Mon, 29 Jul 2024 07:42:20 -0700 (PDT) Received: from e133380.cambridge.arm.com (e133380.arm.com [10.1.197.55]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EA1C43F64C; Mon, 29 Jul 2024 07:41:53 -0700 (PDT) From: Dave Martin To: linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Mark Brown , Joey Gouly Subject: [PATCH] arm64: signal: Update sigcontext reservations table Date: Mon, 29 Jul 2024 15:41:49 +0100 Message-Id: <20240729144149.249096-1-Dave.Martin@arm.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240729_074155_552231_3AD111B6 X-CRM114-Status: GOOD ( 14.95 ) 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 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. * * New records that can exceed this space need to be opt-in for userspace, so * that an expanded signal frame is not generated unexpectedly. The mechanism base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b -- 2.34.1