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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45d9e768acesm13910437f8f.7.2026.05.15.02.24.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 May 2026 02:24:13 -0700 (PDT) Date: Fri, 15 May 2026 10:24:11 +0100 From: David Laight To: Zong Li Cc: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, debug@rivosinc.com, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] riscv: cif: reduce shadow stack size limit from 4GB to 2GB Message-ID: <20260515102411.4d3e868a@pumpkin> In-Reply-To: References: <20260514075036.1432352-1-zong.li@sifive.com> <20260514095605.2c7d8761@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 15 May 2026 11:42:45 +0800 Zong Li wrote: > On Thu, May 14, 2026 at 4:56=E2=80=AFPM David Laight .. > > I also don't understand the rational for just /2 and the 2G upper limit. > > You need 512 nested function calls to even use 4k. > > That would have to be quite deep recursion. =20 >=20 > During the discussions about the ARM GCS v3 series, community pointed > out that a 4G shadow stack might be too large. This size is hard to > support in memory-constrained environments like Android. However, the > size cannot be too small either, or we might face stack overflow > issues. At that time, a perfect size was not decided. It is only VA not real memory so shouldn't make much difference to memory use (except for nommu where the actual memory has to be allocated). But 32bit programs with lots of threads can run out of VA. Increasing the stack VA size by 50% might even give problems for 64bit programs - if they are already reducing the thread stack size avoid running out of VA. I've not checked, but pthread_attr_setstacksize() sets a limit for the thread stack size (which would otherwise default so rlimit(STACK)). I don't believe it should update the rlimit value itself. In which case you are using the wrong size. But for a thread with a very reduced stack (say 128k) you probably only need 1 page of shadow stack, any more could easily lead to running out of VA. -- David 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 C5492CD4851 for ; Fri, 15 May 2026 09:24:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: 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=NaTlbVzEaDEC3XoJV+WWdkw6M8P2im/y+/xcBsT/hpw=; b=LdSYyP31weNI4c /+63kprVmnNun8XUcMi0lhHGs4AtwdOvhN/VoBJZqbsv51ur/fuiNxwamHpAdyQfjPev5lGWZTE8W LtpfL6GWICV5VH4mjq+1sJuZzUy/QTmYhBMD7mwiZKSFZbA2dzHub0QxZRgz2yIG2wtEwXIJ1WZkx iJh5avDXiy1PcLl05KcMs4PlTJ//2KJ4UbfOboukQnqiMMv9bEqbpOrLVXVluuXquaR3r436ZXOAi UJqoXPnD0HlUGsiaqzSRfyksh8Otp6z+qXzM9E2sbYudc1xXPIq+qxfEelRBL6SCIHwqw/ZSgBlSm fsWpbxNQ2I15oWkFTDTA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wNomH-00000007sH3-3uW0; Fri, 15 May 2026 09:24:17 +0000 Received: from mail-wr1-x433.google.com ([2a00:1450:4864:20::433]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wNomF-00000007sGN-3Vtc for linux-riscv@lists.infradead.org; Fri, 15 May 2026 09:24:16 +0000 Received: by mail-wr1-x433.google.com with SMTP id ffacd0b85a97d-43d75312379so479126f8f.1 for ; Fri, 15 May 2026 02:24:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1778837054; x=1779441854; darn=lists.infradead.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=6c5hfgSD5xJa00nFFCK7kaxUQ5uueiePQvAM1Cjtv/s=; b=LZE1VorbEkoBCXbNNb7/JVRP/4iQrZLThubXNAgrQ6TWyC7VyMakBI1jUEjFK40Z9D cdHUVjU6XWXSpeKLUziU7A51JIB6iCdx9OdKHyoGiPPo0bT5sS/5fL3/Zey5qezjv1dl sDvu2RmGLUMJCEXqAPp3tn4YZbCWPuHTf1AyrkKncYGJ3YECHHzueL/k1tlB+YperuYS +xaV9SXZnv6+kwwAI9a0BPu1YgiH3n4Vdp0/jN9q3DmgiCdA2wSD9Fs/rY8fkc0FHaXm s/9NncrY3bqc7xe/o0GeWKgRWWfMe4feoUMbdOQLOdFZlZTb1c8e4aL8k6xaq8Sw+8vP UAXQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778837054; x=1779441854; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=6c5hfgSD5xJa00nFFCK7kaxUQ5uueiePQvAM1Cjtv/s=; b=G+UCUIy70mZ4tMiAxHAXqKC95bM3/ELX1SbE3jGMnK4Q5Vffp7pVrsWLTg/TjLuLyl aKciFAsiO9/pKf8DLXmhTxIS4//lqLTX0r04FcqPcCBRY9IkYybmMWngw4O193eNULL0 fTlQCqPN8jp074fJ+7WMfOH8Db16/5YW+CBUSdedQLgLfudSgDC5gdtgeLMKwFdZFKrs jvnYtxSQDbsQ0FYqoq237I/z9OuQsY3NetCVDJeJz6JdoZKJVF9wYMzNKjUEQjkXQUJi at9qolxIpZFvxRpSAcNlSK6ldFsDerbdqEWhk6fAlguNtOuPFTdI1DtEw4e1j2rfz7II 6zkQ== X-Forwarded-Encrypted: i=1; AFNElJ9+ejGLtqMKPiQH7IF6rS/HJ3nnLeQIrolUPy9EkybM4Fq78Cu/92sD1qpGOsfGSiULVQ2wExRFPbwBnw==@lists.infradead.org X-Gm-Message-State: AOJu0YwJfhmn5PvIzNlpOMY4QuX1Z2DZEUUAC/MfDvjjqM1zScnU5bl9 bDlEM44sZXwFMub0zqekIpPmm8RkUjcc5D8yl7qVG21jCJ843FnLxXwE X-Gm-Gg: Acq92OHunKjbYpXlVCROrk2RTh6KoVWxhqhZyGzkfypdgBo725uMwDMas3s/QIIgDxT eSk+fkU4+XVFoSXxnw6aBPPlxVDLEOvrVy2Jd9fp7nCcF+scdjNfbSLDhCqXK1W2nWqbzOfJqjf 1nUIZJSK93Vd6vP+kwAESaVECPJcYDugkkScQgTVsWVsvdwy3WBItuV68vL/wzvOMm2OtnfWK8e u5JvdoizW0LfeiVR5GujlPZw7UYJaqfVWwWPzZJ5ttVgkoTG3pxhWpA/pb9axEEC4JtzabPntdx Kfj6NLYWQiIVKmUQLdl7M7tZsvzalj8K4r6JOOqbjbT+vZk6YoZP0hOcJEFzLVui5SnDya5z/Wk 6Ssh7WsJaLqcNJShBEs/kANGdAUJlkmnqEkY1ypM+P+vvlVDfyCp+IzBnHh+Y1p9zNgbBZlzzNw VMUfka48/HsJ7/SBZa8OsfV6PfaQP2Y+jGEeOhYIJ/ecE9Xlox5+BNYXRtbw/Q X-Received: by 2002:a05:6000:290f:b0:43e:a75e:352 with SMTP id ffacd0b85a97d-45e5b73b1d5mr4833404f8f.4.1778837053558; Fri, 15 May 2026 02:24:13 -0700 (PDT) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45d9e768acesm13910437f8f.7.2026.05.15.02.24.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 May 2026 02:24:13 -0700 (PDT) Date: Fri, 15 May 2026 10:24:11 +0100 From: David Laight To: Zong Li Cc: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, debug@rivosinc.com, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] riscv: cif: reduce shadow stack size limit from 4GB to 2GB Message-ID: <20260515102411.4d3e868a@pumpkin> In-Reply-To: References: <20260514075036.1432352-1-zong.li@sifive.com> <20260514095605.2c7d8761@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260515_022415_893859_B0712409 X-CRM114-Status: GOOD ( 15.16 ) X-BeenThere: linux-riscv@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="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org T24gRnJpLCAxNSBNYXkgMjAyNiAxMTo0Mjo0NSArMDgwMApab25nIExpIDx6b25nLmxpQHNpZml2 ZS5jb20+IHdyb3RlOgoKPiBPbiBUaHUsIE1heSAxNCwgMjAyNiBhdCA0OjU24oCvUE0gRGF2aWQg TGFpZ2h0Ci4uCj4gPiBJIGFsc28gZG9uJ3QgdW5kZXJzdGFuZCB0aGUgcmF0aW9uYWwgZm9yIGp1 c3QgLzIgYW5kIHRoZSAyRyB1cHBlciBsaW1pdC4KPiA+IFlvdSBuZWVkIDUxMiBuZXN0ZWQgZnVu Y3Rpb24gY2FsbHMgdG8gZXZlbiB1c2UgNGsuCj4gPiBUaGF0IHdvdWxkIGhhdmUgdG8gYmUgcXVp dGUgZGVlcCByZWN1cnNpb24uICAKPiAKPiBEdXJpbmcgdGhlIGRpc2N1c3Npb25zIGFib3V0IHRo ZSBBUk0gR0NTIHYzIHNlcmllcywgY29tbXVuaXR5IHBvaW50ZWQKPiBvdXQgdGhhdCBhIDRHIHNo YWRvdyBzdGFjayBtaWdodCBiZSB0b28gbGFyZ2UuIFRoaXMgc2l6ZSBpcyBoYXJkIHRvCj4gc3Vw cG9ydCBpbiBtZW1vcnktY29uc3RyYWluZWQgZW52aXJvbm1lbnRzIGxpa2UgQW5kcm9pZC4gSG93 ZXZlciwgdGhlCj4gc2l6ZSBjYW5ub3QgYmUgdG9vIHNtYWxsIGVpdGhlciwgb3Igd2UgbWlnaHQg ZmFjZSBzdGFjayBvdmVyZmxvdwo+IGlzc3Vlcy4gQXQgdGhhdCB0aW1lLCBhIHBlcmZlY3Qgc2l6 ZSB3YXMgbm90IGRlY2lkZWQuCgpJdCBpcyBvbmx5IFZBIG5vdCByZWFsIG1lbW9yeSBzbyBzaG91 bGRuJ3QgbWFrZSBtdWNoIGRpZmZlcmVuY2UgdG8gbWVtb3J5CnVzZSAoZXhjZXB0IGZvciBub21t dSB3aGVyZSB0aGUgYWN0dWFsIG1lbW9yeSBoYXMgdG8gYmUgYWxsb2NhdGVkKS4KCkJ1dCAzMmJp dCBwcm9ncmFtcyB3aXRoIGxvdHMgb2YgdGhyZWFkcyBjYW4gcnVuIG91dCBvZiBWQS4KSW5jcmVh c2luZyB0aGUgc3RhY2sgVkEgc2l6ZSBieSA1MCUgbWlnaHQgZXZlbiBnaXZlIHByb2JsZW1zIGZv ciA2NGJpdApwcm9ncmFtcyAtIGlmIHRoZXkgYXJlIGFscmVhZHkgcmVkdWNpbmcgdGhlIHRocmVh ZCBzdGFjayBzaXplIGF2b2lkCnJ1bm5pbmcgb3V0IG9mIFZBLgoKSSd2ZSBub3QgY2hlY2tlZCwg YnV0IHB0aHJlYWRfYXR0cl9zZXRzdGFja3NpemUoKSBzZXRzIGEgbGltaXQgZm9yIHRoZQp0aHJl YWQgc3RhY2sgc2l6ZSAod2hpY2ggd291bGQgb3RoZXJ3aXNlIGRlZmF1bHQgc28gcmxpbWl0KFNU QUNLKSkuCkkgZG9uJ3QgYmVsaWV2ZSBpdCBzaG91bGQgdXBkYXRlIHRoZSBybGltaXQgdmFsdWUg aXRzZWxmLgpJbiB3aGljaCBjYXNlIHlvdSBhcmUgdXNpbmcgdGhlIHdyb25nIHNpemUuCgpCdXQg Zm9yIGEgdGhyZWFkIHdpdGggYSB2ZXJ5IHJlZHVjZWQgc3RhY2sgKHNheSAxMjhrKSB5b3UgcHJv YmFibHkgb25seQpuZWVkIDEgcGFnZSBvZiBzaGFkb3cgc3RhY2ssIGFueSBtb3JlIGNvdWxkIGVh c2lseSBsZWFkIHRvIHJ1bm5pbmcgb3V0Cm9mIFZBLgoKLS0gRGF2aWQKCl9fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCmxpbnV4LXJpc2N2IG1haWxpbmcgbGlz dApsaW51eC1yaXNjdkBsaXN0cy5pbmZyYWRlYWQub3JnCmh0dHA6Ly9saXN0cy5pbmZyYWRlYWQu b3JnL21haWxtYW4vbGlzdGluZm8vbGludXgtcmlzY3YK