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 1E5F0CD4F3C for ; Mon, 18 May 2026 09:57:49 +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=mjCPPGyMF2vcKnYiuDo5TMnkQWFeo5wh2EhmBa+1NbE=; b=nhrAFxeBnNNo/J hiMjpL2TJATVf4ExY87e++W/LfxiVz26cQG4raHXnKZg7xPBYqFB21B9O2kFIbxQVAJvsnn2ceK4R I/cwdCXK6ghhwYThzSZYMAGRpGg+I0LkvGA0EzrAS+02ppiWUws96vi1dKyz5EMsVZ8pORhcMubcP IzNBxMh7P0pXWxXCx06BZsds9I1pDubs272RWzTq8o2mK4o6xBbv4h7SM46pC6WkjjovtmFJKUvNP IEXjZ3LsjoCBs6J8O73PbLc1GNAmwPs1SnvT8h/2OYmDfFGj9DfVUy0TaSdCIKc560P6zIDkfAqly qBdhE5D9xXwc/y+PViwA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wOujE-0000000F7Jf-1WX0; Mon, 18 May 2026 09:57:40 +0000 Received: from desiato.infradead.org ([2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wOujC-0000000F7IZ-1tFj for linux-riscv@bombadil.infradead.org; Mon, 18 May 2026 09:57:38 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Content-Transfer-Encoding:Content-Type :MIME-Version:References:In-Reply-To:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=HT0Lf2/mFgKxOu+qdEtEaudYEyue/pxbGLR/tX7Yu8c=; b=bV+zB+COkSsiY36W03Zvc7Z51A B2ieQ1AzZzFn49wo6tbjO1/kmk2LbGSRbbRKuCX3LZmslg2tp2kyuG9iaFPa+5gCnLpguLVLi8OtA NFaPOcS+jO1yBmLKDuOY8wLpWgNNbEor7CYE4ff0bXDhOk03QDgLQVS3O0YAAQoWwUSbLt7UnDavf fb5mmx1qYT6jdYOAaTPAlPxarcoo2C4m+ON4C9vrp0dr8OG15sOf9FonBGcWhXizBthiU/R6DXtjS 8eAIrwXteB4djBJOGJsHSCqtAIqaaMUdC6oh6P0pQiyhxA7TRupsP2NxnnfewwCPLZApPTjRHf3mq FvwckyaA==; Received: from mail-wr1-x430.google.com ([2a00:1450:4864:20::430]) by desiato.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wOuj3-0000000AfEe-0BQY for linux-riscv@lists.infradead.org; Mon, 18 May 2026 09:57:35 +0000 Received: by mail-wr1-x430.google.com with SMTP id ffacd0b85a97d-43d73422431so1307495f8f.2 for ; Mon, 18 May 2026 02:57:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1779098247; x=1779703047; 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=HT0Lf2/mFgKxOu+qdEtEaudYEyue/pxbGLR/tX7Yu8c=; b=heuowZXBbVG9XmhvMFAQvXssbhjU/M9Yhuhf2LqFvUOUVaQfSxv/WYkVhgcMWvWFjf LB9ncr1lW7fpZeXCE7Xr1HMG11G+tcFeQrV+u83zvGM3EQ/wqPl7q4SqOqZK3/VW9zSe pAtxmhVvJfw4UlXGbyGR99TC7wgVQHCR1zUGn7HE1t05mVBmLJvEJ48wFTKKEfA7ex0C m08Ba4aXLCAWhIkRvP8Mp9tFNN9+wQN6URbOP2zyvaRN7zJXtSw+MzEEjEL1P/j9wMIv jyzmEDq4G6hcsyDA3rpwfdxx43xDpf9dLNlPO9iVUGN7CAPhuM524OwdQPDt9WK8o21Q PctQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779098247; x=1779703047; 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=HT0Lf2/mFgKxOu+qdEtEaudYEyue/pxbGLR/tX7Yu8c=; b=EOam8eSMJC1Avf7+rASCaMSD4qSG+YQQYpWH3K6ELufNTRXiwHm+a/DPxERWfxCVZp SV2v+vhtjj3xvn7gqdziWUPoiSVEc6vAL7ZFl9TkoVpyTWW8rxcGgsU4TA4pFtLZwoAf ZLTuHIoX3VtIwztSju/d3m8rLzF5vxYsJ2mbbnDnwJO8wsZmW6YHFd8MTdXCmkqc4KK+ dmWN7/O659Xoog434g3hd4pt2Ie3Yx1KznhZe052wH4FXVtq+gOAT7NrgGtaAFsIs0MU pm2pUdC4qDAQti9nGc+NlPTPHEy/8ePFaLJKJW/tjnSt7NAxmv3DALsJ+CNqGJr4FzDV cBaA== X-Forwarded-Encrypted: i=1; AFNElJ8L5uvaQH+Q3uWMh8Ec37e3STw4R319F9vAYg5uaJPQH9kLGp4QSCZven9GOiq72gDkogDmW7wib+jZMQ==@lists.infradead.org X-Gm-Message-State: AOJu0YwG4Fco+RLlwkHoq4u1augODPEm6vmPviRS++1LxQ3QdjPK16Bm LWONL+I1pwl+Ia3mQZKBROCUnhhgsLhEPJkrn8zQTDmBYy5n/hGE9aMH X-Gm-Gg: Acq92OE8ayA8q0lKDpaBN9Gmn8QDhx5V8PstpMT5vNBFHNt6R5X3pJP8YZ4SX7rqA/7 8OAIdy1AzVZ9c2I348SKWMjhU8ZlgbMCUbuYTur3a9lyzktaitBoZdHJVDsMZPMb+LxWTTmJtqq TcpQTg3C3AK/GFwOGqyYWN5yd248yE35E7g/xeAzRf/eb/dULVFAgG3NY1dg8PvJbiY1pjGbV4B NKdoiF4oQsAgceo5qEZSHQ5XJbCYLBwHLALr7eeTxB2q6SuHFAz0c14sDezdszrAS9VBbSUno18 dty1+Q9iGflOnDax6TxYxLUOLpLOoCfxLjEvIMHEYYYaH6djMFZRn/SYBG2KEGTrjbG0XdZD4KS azk6SEfha8MlYHTplt017ttaZj5rEFuOsj+xJaPvt1rQqa3UuG/QUDDZXV6lRqMrFmdiAc+vWgz R9Dw3R5WSsVCH1n5l8vSyyry68hD/Tf5D1f5r64CvS5W0rn5qaOfchqH56XIzNmrwKKzB86Aa2I gE= X-Received: by 2002:a05:6000:2304:b0:441:1c95:17e7 with SMTP id ffacd0b85a97d-45e5c5c9e11mr23052887f8f.15.1779098247199; Mon, 18 May 2026 02:57:27 -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-45da0a19a0csm34266191f8f.20.2026.05.18.02.57.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 May 2026 02:57:26 -0700 (PDT) Date: Mon, 18 May 2026 10:57:25 +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: <20260518105725.7afe7a4c@pumpkin> In-Reply-To: References: <20260514075036.1432352-1-zong.li@sifive.com> <20260514095605.2c7d8761@pumpkin> <20260515102411.4d3e868a@pumpkin> <20260515201613.243ea49b@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-20260518_105730_242504_A5A5AF80 X-CRM114-Status: GOOD ( 46.88 ) 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 T24gTW9uLCAxOCBNYXkgMjAyNiAxMTo1NDozMiArMDgwMApab25nIExpIDx6b25nLmxpQHNpZml2 ZS5jb20+IHdyb3RlOgoKPiBPbiBTYXQsIE1heSAxNiwgMjAyNiBhdCAzOjE24oCvQU0gRGF2aWQg TGFpZ2h0Cj4gPGRhdmlkLmxhaWdodC5saW51eEBnbWFpbC5jb20+IHdyb3RlOgo+ID4KPiA+IE9u IEZyaSwgMTUgTWF5IDIwMjYgMjI6Mjk6MDUgKzA4MDAKPiA+IFpvbmcgTGkgPHpvbmcubGlAc2lm aXZlLmNvbT4gd3JvdGU6Cj4gPiAgCj4gPiA+IE9uIEZyaSwgTWF5IDE1LCAyMDI2IGF0IDU6MjTi gK9QTSBEYXZpZCBMYWlnaHQKPiA+ID4gPGRhdmlkLmxhaWdodC5saW51eEBnbWFpbC5jb20+IHdy b3RlOiAgCj4gPiA+ID4KPiA+ID4gPiBPbiBGcmksIDE1IE1heSAyMDI2IDExOjQyOjQ1ICswODAw Cj4gPiA+ID4gWm9uZyBMaSA8em9uZy5saUBzaWZpdmUuY29tPiB3cm90ZToKPiA+ID4gPiAgCj4g PiA+ID4gPiBPbiBUaHUsIE1heSAxNCwgMjAyNiBhdCA0OjU24oCvUE0gRGF2aWQgTGFpZ2h0ICAK PiA+ID4gPiAuLiAgCj4gPiA+ID4gPiA+IEkgYWxzbyBkb24ndCB1bmRlcnN0YW5kIHRoZSByYXRp b25hbCBmb3IganVzdCAvMiBhbmQgdGhlIDJHIHVwcGVyIGxpbWl0Lgo+ID4gPiA+ID4gPiBZb3Ug bmVlZCA1MTIgbmVzdGVkIGZ1bmN0aW9uIGNhbGxzIHRvIGV2ZW4gdXNlIDRrLgo+ID4gPiA+ID4g PiBUaGF0IHdvdWxkIGhhdmUgdG8gYmUgcXVpdGUgZGVlcCByZWN1cnNpb24uICAKPiA+ID4gPiA+ Cj4gPiA+ID4gPiBEdXJpbmcgdGhlIGRpc2N1c3Npb25zIGFib3V0IHRoZSBBUk0gR0NTIHYzIHNl cmllcywgY29tbXVuaXR5IHBvaW50ZWQKPiA+ID4gPiA+IG91dCB0aGF0IGEgNEcgc2hhZG93IHN0 YWNrIG1pZ2h0IGJlIHRvbyBsYXJnZS4gVGhpcyBzaXplIGlzIGhhcmQgdG8KPiA+ID4gPiA+IHN1 cHBvcnQgaW4gbWVtb3J5LWNvbnN0cmFpbmVkIGVudmlyb25tZW50cyBsaWtlIEFuZHJvaWQuIEhv d2V2ZXIsIHRoZQo+ID4gPiA+ID4gc2l6ZSBjYW5ub3QgYmUgdG9vIHNtYWxsIGVpdGhlciwgb3Ig d2UgbWlnaHQgZmFjZSBzdGFjayBvdmVyZmxvdwo+ID4gPiA+ID4gaXNzdWVzLiBBdCB0aGF0IHRp bWUsIGEgcGVyZmVjdCBzaXplIHdhcyBub3QgZGVjaWRlZC4gIAo+ID4gPiA+Cj4gPiA+ID4gSXQg aXMgb25seSBWQSBub3QgcmVhbCBtZW1vcnkgc28gc2hvdWxkbid0IG1ha2UgbXVjaCBkaWZmZXJl bmNlIHRvIG1lbW9yeQo+ID4gPiA+IHVzZSAoZXhjZXB0IGZvciBub21tdSB3aGVyZSB0aGUgYWN0 dWFsIG1lbW9yeSBoYXMgdG8gYmUgYWxsb2NhdGVkKS4KPiA+ID4gPiAgCj4gPiA+Cj4gPiA+IFlv dSByYWlzZSBhIHZhbGlkIHBvaW50IHRoYXQgc2hhZG93IHN0YWNrcyBhcmUgcHJpbWFyaWx5IGEg VkEKPiA+ID4gYWxsb2NhdGlvbi4gSG93ZXZlciwgaW4gTGludXgsIHRoZSBtZW1vcnkgb3ZlcmNv bW1pdCBtZWNoYW5pc20gY3JlYXRlcwo+ID4gPiBhIHByYWN0aWNhbCBsaW5rIGJldHdlZW4gVkEg YWxsb2NhdGlvbiBhbmQgcGh5c2ljYWwgbWVtb3J5IGNhcGFjaXR5Lgo+ID4gPiBBcyBJIG1lbnRp b25lZCBpbiB0aGUgY29tbWl0IG1lc3NhZ2UsIG1lbW9yeSBhbGxvY2F0aW9uIHdpbGwgZmFpbCB3 aGVuCj4gPiA+IHRoZSBvdmVyY29tbWl0IG1vZGUgaXMgc2V0IHRvIE9WRVJDT01NSVRfR1VFU1Mg b3IgT1ZFUkNPTU1JVF9ORVZFUi4KPiA+ID4KPiA+ID4gSW4gX192bV9lbm91Z2hfbWVtb3J5Ogo+ ID4gPiAgICAgICAgIGlmIChwYWdlcyA+IHRvdGFscmFtX3BhZ2VzKCkgKyB0b3RhbF9zd2FwX3Bh Z2VzKQo+ID4gPiAgICAgICAgICAgICAgICAgZ290byBlcnJvcjsKPiA+ID4KPiA+ID4gTWFueSBw YWdlIHJlcXVlc3RzIGZvciBWQSB3aWxsIGZhaWwgaWYgdGhlIHJlcXVlc3RlZCBzaXplIGV4Y2Vl ZHMgdGhlCj4gPiA+IHN5c3RlbSdzIHRvdGFsIFJBTSBwbHVzIFN3YXAuIE9uIG1lbW9yeS1jb25z dHJhaW5lZCBzeXN0ZW1zLAo+ID4gPiBhbGxvY2F0aW5nIGEgbWFzc2l2ZSA0R0Igc2hhZG93IHN0 YWNrIHBlciB0aHJlYWQgd291bGQgaW1tZWRpYXRlbHkKPiA+ID4gdHJpZ2dlciB0aGlzIGVycm9y LiAgCj4gPgo+ID4gQnV0IHJlZHVjaW5nIHRoZSBzaXplIGJ5IGhhbGYgbWFrZXMgbGl0dGxlIGRp ZmZlcmVuY2UuCj4gPiBZb3UnZCBuZWVkIGEgbXVjaCBiaWdnZXIgcmVkdWN0aW9uIHRvIG1ha2Ug YW55IHJlYWwgZGlmZmVyZW5jZS4KPiA+ICAKPiAKPiBJIGFncmVlIHdpdGggeW91IHRoYXQgYSBz bWFsbGVyIHNpemUgd291bGQgY292ZXIgbW9yZSBjYXNlcy4gSSBhbSB2ZXJ5Cj4gb3BlbiB0byB5 b3VyIGlkZWFzIHJlZ2FyZGluZyB0aGUgc2l6ZS4gV291bGQgeW91IHByZWZlciB0byB1c2UgMUdC IG9yCj4gNTEyTUIgYXMgdGhlIGRlZmF1bHQgaW5zdGVhZD8KPiBBcyBJIG1lbnRpb25lZCBpbiBt eSBwcmV2aW91cyBlbWFpbHMsIHVzaW5nIDJHQiBzZWVtcyB0byBiZSBhIHNhZmUKPiBzdGFydGlu ZyBwb2ludC4gVGhpcyBpcyBiZWNhdXNlIGl0IGlzIGFscmVhZHkgYWNjZXB0ZWQgYnkgdGhlCj4g Y29tbXVuaXR5IGFuZCB0aGUgQW5kcm9pZCBzeXN0ZW0gKGluIEdDUyBpbXBsZW1lbnRhdGlvbiku Cj4gQWRkaXRpb25hbGx5LCBhbHRob3VnaCB0aGUgQ0ZJIGZlYXR1cmUgZG9lc24ndCBzdXBwb3J0 IDMyLWJpdCBzeXN0ZW1zCj4geWV0LCBub3JtYWwgMzItYml0IHN5c3RlbXMgY2FuIG9ubHkgc3Vw cG9ydCB1cCB0byA0R0Igb2YgcGh5c2ljYWwKPiBtZW1vcnkuIElmIHRoZSBkZWZhdWx0IHNoYWRv dyBzdGFjayBzaXplIGlzIDRHQiwgaXQgd291bGQgYmUgYWxtb3N0Cj4gaW1wb3NzaWJsZSB0byBy dW4gb24gYSAzMi1iaXQgc3lzdGVtLiBVc2luZyBhdCBsZWFzdCAyR0IgY2FuIGhlbHAKPiBhdm9p ZCB0aGlzIGlzc3VlIGluIHRoZSBmdXR1cmUuIElmIHlvdSBkb24ndCBoYXZlIGEgcHJlZmVycmVk IGRlZmF1bHQKPiB2YWx1ZSwgbWF5YmUgd2UgY291bGQgc3RhcnQgd2l0aCAyRz8KCkkndmUgbm8g cmVhbCBpZGVhIC0gbm90ZSB0aGF0IHRoZSBybGltaXQgdmFsdWUgc2hvdWxkIGJlIHNtYWxsIGZv ciAzMmJpdAoob3IgYXQgbGVhc3QgdGhlIGFjdHVhbCBzdGFjayBpcyBzbWFsbCByZWdhcmRsZXNz IG9mIHRoZSBybGltaXQgdmFsdWUpLgpUaGUgMkcgaXMganVzdCBhbiB1cHBlciBib3VuZCAtIHBy b2JhYmx5IG1hdGNoaW5nIHRoZSA0RyB1cHBlciBib3VuZApmb3IgdGhlIDY0Yml0IHN0YWNrIGl0 c2VsZi4KCkRvbid0IGZvY3VzIG9uIHRoZSAyRyBsaW1pdCwgYnV0IG9uIHRoZSBybGltaXQoU1RB Q0spLzIgKG9yIHJhdGhlciB0aGUgc2l6ZQpvZiB0aGUgbm9ybWFsIHN0YWNrKS4KT24gbXkgc3lz dGVtcyB0aGUgZGVmYXVsdCBzb2Z0IGxpbWl0IGlzIDhNLCBhIDRNIHNoYWRvdyBzdGFjayBzdXBw b3J0cyA1MTJrCm5lc3RlZCBmdW5jdGlvbiBjYWxscyAoNjRiaXQpIC0gbm9uZSBvZiB3aGljaCBj YW4gaGF2ZSBhbnkgbG9jYWwgZGF0YS4KSW4gcmVhbGl0eSBwcm9ncmFtcyB0aGF0IHVzZSBhIGxv dCBvZiBzdGFjayBhbGxvY2F0ZSBsYXJnZSBidWZmZXJzIG9uIHN0YWNrLAp0aGV5IGRvbid0IGhh dmUgc2lsbHkgZGVwdGhzIG9mIHJlY3Vyc2l2ZSBmdW5jdGlvbnMgd2l0aCBubyBsb2NhbCBkYXRh LgoKSSd2ZSBqdXN0IGxvb2tlZCBhdCB2bWxpbnV4Lm8gLSB3aGljaCB3b24ndCBiZSByZXByZXNl bnRhdGl2ZSBvZiB1c2Vyc3BhY2UhCldoaWxlIHRoZXJlIGFyZSBhIGxvdCBvZiBmdW5jdGlvbnMg d2l0aCBzbWFsbCBzdGFjayBmcmFtZSAoc3ViICQweDEwLCVyc3ApCnRoZXkgdGVuZCB0byBoYXZl IHNhdmVkIGEgZmV3IHJlZ2lzdGVycyBpbiBzdGFjayBmaXJzdC4KVGhlIG1ham9yaXR5IHdpbGwg aGF2ZSBhIHN0YWNrIGRlbHRhIG9mIG92ZXIgNjQgYnl0ZXMuClRoYXQgY29ycmVzcG9uZHMgdG8g cmxpbWl0KFNUQUNLKS84IGFuZCBldmVuIHRoYXQgaXMgY29uc2VydmF0aXZlLgoKSSdkIHN1c3Bl Y3QgdGhhdCBjb3VsZCBzYWZlbHkgaGFsdmUgdGhhdCBhZ2Fpbi4KCkFjdHVhbGx5IHdvdWxkIGl0 IGJlIHBvc3NpYmxlIHRvIGluaXRpYWxseSBqdXN0IGFsbG9jYXRlIG9uZSBwYWdlPwpJZiB5b3Ug Z2V0IGFuIG92ZXJmbG93IGZhdWx0IG9uIHRoZSBzaGFkb3cgc3RhY2sgSSB0aGluayB5b3UgY2Fu CnNhZmVseSByZWFsbG9jYXRlIGl0IGF0IGFuIGVudGlyZWx5IGRpZmZlcmVudCB1c2VyIHZpcnR1 YWwgYWRkcmVzcy4KVGhhdCB3b3VsZCByZW1vdmUgYWxsIHRoZSBwcm9ibGVtcyBvdmVyIGNvbW1p dHRpbmcgYSBsb3Qgb2Ygc3dhcC4KTW9zdCB0aHJlYWRzIHdpbGwgbmV2ZXIgZG8gdGhlIDUxMiBu ZXN0ZWQgY2FsbHMgbmVlZGVkIHRvIGJsb3cgdGhlIHN0YWNrLgoKLS0gRGF2aWQKCj4gCj4gCj4g PiAtLSBEYXZpZAo+ID4gIAo+ID4gPiAgCj4gPiA+ID4gQnV0IDMyYml0IHByb2dyYW1zIHdpdGgg bG90cyBvZiB0aHJlYWRzIGNhbiBydW4gb3V0IG9mIFZBLgo+ID4gPiA+IEluY3JlYXNpbmcgdGhl IHN0YWNrIFZBIHNpemUgYnkgNTAlIG1pZ2h0IGV2ZW4gZ2l2ZSBwcm9ibGVtcyBmb3IgNjRiaXQK PiA+ID4gPiBwcm9ncmFtcyAtIGlmIHRoZXkgYXJlIGFscmVhZHkgcmVkdWNpbmcgdGhlIHRocmVh ZCBzdGFjayBzaXplIGF2b2lkCj4gPiA+ID4gcnVubmluZyBvdXQgb2YgVkEuCj4gPiA+ID4KPiA+ ID4gPiBJJ3ZlIG5vdCBjaGVja2VkLCBidXQgcHRocmVhZF9hdHRyX3NldHN0YWNrc2l6ZSgpIHNl dHMgYSBsaW1pdCBmb3IgdGhlCj4gPiA+ID4gdGhyZWFkIHN0YWNrIHNpemUgKHdoaWNoIHdvdWxk IG90aGVyd2lzZSBkZWZhdWx0IHNvIHJsaW1pdChTVEFDSykpLgo+ID4gPiA+IEkgZG9uJ3QgYmVs aWV2ZSBpdCBzaG91bGQgdXBkYXRlIHRoZSBybGltaXQgdmFsdWUgaXRzZWxmLgo+ID4gPiA+IElu IHdoaWNoIGNhc2UgeW91IGFyZSB1c2luZyB0aGUgd3Jvbmcgc2l6ZS4KPiA+ID4gPgo+ID4gPiA+ IEJ1dCBmb3IgYSB0aHJlYWQgd2l0aCBhIHZlcnkgcmVkdWNlZCBzdGFjayAoc2F5IDEyOGspIHlv dSBwcm9iYWJseSBvbmx5Cj4gPiA+ID4gbmVlZCAxIHBhZ2Ugb2Ygc2hhZG93IHN0YWNrLCBhbnkg bW9yZSBjb3VsZCBlYXNpbHkgbGVhZCB0byBydW5uaW5nIG91dAo+ID4gPiA+IG9mIFZBLgo+ID4g PiA+Cj4gPiA+ID4gLS0gRGF2aWQgIAo+ID4gPiAgCj4gPiAgCgoKX19fX19fX19fX19fX19fX19f X19fX19fX19fX19fX19fX19fX19fX19fX19fX18KbGludXgtcmlzY3YgbWFpbGluZyBsaXN0Cmxp bnV4LXJpc2N2QGxpc3RzLmluZnJhZGVhZC5vcmcKaHR0cDovL2xpc3RzLmluZnJhZGVhZC5vcmcv bWFpbG1hbi9saXN0aW5mby9saW51eC1yaXNjdgo= From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f46.google.com (mail-wr1-f46.google.com [209.85.221.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4BA76175A62 for ; Mon, 18 May 2026 09:57:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.46 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779098251; cv=none; b=BvXB1dMUbdWKiCuT4wSOSMfyyo/012EpogFk4lymqsVZ+Nswjw8oYTN0nPkjz3v1kVzwM8Nmg7WKyVYGoYo41z5QsksxDIk8nVXP4q0S7cXcBpSX5yNVV4K/KqtchZtlQ5Gl1q3ZhlwVOVLnCnIj8VjwLO2RC/qznNky3cPklog= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779098251; c=relaxed/simple; bh=1/SwIiA5aU2s7wXzzcGa+fBfKjwCMi7XmJtyNR0b2Vs=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=RvxE2TFLU8pyG9ZqBXuGEPyA9p0ce4CtxPrAocsj2pasiEQBOjjMsstxCNAML2tIYzPt1srzhnPfNzMuyzYOCZcV9rns8yQ9CJWIBjybFLr8eH/LUVeHngoI0uWj5yxdteXwS2QnbcBg7DfPGBKBHZQFJoW6pFpA9DwmL2FwxG0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=KWMwacne; arc=none smtp.client-ip=209.85.221.46 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KWMwacne" Received: by mail-wr1-f46.google.com with SMTP id ffacd0b85a97d-44a14580111so1504331f8f.0 for ; Mon, 18 May 2026 02:57:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1779098247; x=1779703047; darn=vger.kernel.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=HT0Lf2/mFgKxOu+qdEtEaudYEyue/pxbGLR/tX7Yu8c=; b=KWMwacnedd1XT5HxG8atZvqDIFBZmVL1FNUeSQgqks8v8ridooiaMW0Qd03PwARUCe zu2xBEiiRIslDzgmHLyVgFsUBOtZLIVqqzppCWbMuL77ZCyxiHCjSLn4ybnfbFebUSu/ 6hwOot+rYiLqNAUda28SGK/Hwb+yxHVcnjNpeG8JAGy1DRRPi+5tY3rUS0gF9RcUxx6U A+x3Otb79KkOkDcATIWAQLa6UGPVfV7YkthHTiiPoqN/2DRBVCdmT6ntVJgeGFGpQNNv R4Lg6dxDvPFl4uWR2/1rDsu61giCUpEbuh+nV90Kcv82yE++ohcCDO/v1QCJilYvxHSZ 0M2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779098247; x=1779703047; 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=HT0Lf2/mFgKxOu+qdEtEaudYEyue/pxbGLR/tX7Yu8c=; b=KIBnx6TRk4dx9hPu+JsYn3HKl41MCjK0zlxLD1Zr92448MfjCgluAG8Y5B7Z9rXIe+ 6jmFkwcBn2KCnjsoX8niDv1XWy6pF9k5BbZFlVbKQOz1PxlC/JbglYosQkQG7+p5zr/3 YleevFV/FQgH0TwrLOj/+TORmenj0ulhOrE5CFUKQzMW405K7GHzhwV24a5qaM8+vfBs 1mf25E052Vu77r124vsQWz5aM0GRsksWJMjzei5ySCQ7HrO7Yo87B45xmPfzuNV2/bam EPfKJ1wH9C6Ezw3nB6VvmKQVhIR06Ud95LXhMkfuz0vpoHiww5vCHqSLINzz+VKbJfun UlBQ== X-Forwarded-Encrypted: i=1; AFNElJ+mOgj+J/6i5H3Rlmk6RXqLis7APZFbZtw2MCl7+Bcx5UDnIZKueN1y5bmLvFNmuWtZJRow3XOd/IqHdiM=@vger.kernel.org X-Gm-Message-State: AOJu0YzcDevvV7vRr38fVWyLKtrDelNWTmbNm7pv++Nj01gJW1VTF6Xe oQTM6ZySmH+XfmNVPSXgLGwR/XN4aPx2bCG5wcgJL5r90WiygBKnOX+V X-Gm-Gg: Acq92OHFMbYOuykYT4vAutdpMYmppuJT8wmj3XUk5pytI09Jue6Bx8zJv2I9U/ZHT3T g4CLhO0HGI1G5vGhBru7b/fG97oK1kS4+MRWJY947Ueo6xXI9cCoeBr8X32zBQ0rCxiYEEOOWNa ncJ0VXl2D0v7RPIqo7N0dJOqa76gm/PhvEYk9SdGZlD40//xL3daE2UuwG1/xgw+Xxve2bh9sum RxycUnbzHk753TQbJNf8WHAncckROGVDPB/VE8n7t9OVx4C0yCXQViRhwi6odoa43m1GBQlB9cJ 72LUzGY9TCUmycqrr3Hv48fhKXDoVkpcGnOBpCI9+Lq9OTcXUXP5b5CJW12ABMFibNwqGJp49kL DtL49I1GTGBAmTY3Wp6zFcMb/vmSTVljJ0JyJkIyQF1C94D5LUhc2IPfYZFE1vqF6VLTlP+exZm lArToSSz31uh+V81P3nqjTC5+ABWNB5NUy5BlR710giFWUTJyWyij0FawFkL5ePUDadTz3qTEim O0= X-Received: by 2002:a05:6000:2304:b0:441:1c95:17e7 with SMTP id ffacd0b85a97d-45e5c5c9e11mr23052887f8f.15.1779098247199; Mon, 18 May 2026 02:57:27 -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-45da0a19a0csm34266191f8f.20.2026.05.18.02.57.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 May 2026 02:57:26 -0700 (PDT) Date: Mon, 18 May 2026 10:57:25 +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: <20260518105725.7afe7a4c@pumpkin> In-Reply-To: References: <20260514075036.1432352-1-zong.li@sifive.com> <20260514095605.2c7d8761@pumpkin> <20260515102411.4d3e868a@pumpkin> <20260515201613.243ea49b@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 Mon, 18 May 2026 11:54:32 +0800 Zong Li wrote: > On Sat, May 16, 2026 at 3:16=E2=80=AFAM David Laight > wrote: > > > > On Fri, 15 May 2026 22:29:05 +0800 > > Zong Li wrote: > > =20 > > > On Fri, May 15, 2026 at 5:24=E2=80=AFPM David Laight > > > wrote: =20 > > > > > > > > On Fri, 15 May 2026 11:42:45 +0800 > > > > Zong Li wrote: > > > > =20 > > > > > On Thu, May 14, 2026 at 4:56=E2=80=AFPM David Laight =20 > > > > .. =20 > > > > > > I also don't understand the rational for just /2 and the 2G upp= er limit. > > > > > > You need 512 nested function calls to even use 4k. > > > > > > That would have to be quite deep recursion. =20 > > > > > > > > > > During the discussions about the ARM GCS v3 series, community poi= nted > > > > > 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. =20 > > > > > > > > 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). > > > > =20 > > > > > > You raise a valid point that shadow stacks are primarily a VA > > > allocation. However, in Linux, the memory overcommit mechanism creates > > > a practical link between VA allocation and physical memory capacity. > > > As I mentioned in the commit message, memory allocation will fail when > > > the overcommit mode is set to OVERCOMMIT_GUESS or OVERCOMMIT_NEVER. > > > > > > In __vm_enough_memory: > > > if (pages > totalram_pages() + total_swap_pages) > > > goto error; > > > > > > Many page requests for VA will fail if the requested size exceeds the > > > system's total RAM plus Swap. On memory-constrained systems, > > > allocating a massive 4GB shadow stack per thread would immediately > > > trigger this error. =20 > > > > But reducing the size by half makes little difference. > > You'd need a much bigger reduction to make any real difference. > > =20 >=20 > I agree with you that a smaller size would cover more cases. I am very > open to your ideas regarding the size. Would you prefer to use 1GB or > 512MB as the default instead? > As I mentioned in my previous emails, using 2GB seems to be a safe > starting point. This is because it is already accepted by the > community and the Android system (in GCS implementation). > Additionally, although the CFI feature doesn't support 32-bit systems > yet, normal 32-bit systems can only support up to 4GB of physical > memory. If the default shadow stack size is 4GB, it would be almost > impossible to run on a 32-bit system. Using at least 2GB can help > avoid this issue in the future. If you don't have a preferred default > value, maybe we could start with 2G? I've no real idea - note that the rlimit value should be small for 32bit (or at least the actual stack is small regardless of the rlimit value). The 2G is just an upper bound - probably matching the 4G upper bound for the 64bit stack itself. Don't focus on the 2G limit, but on the rlimit(STACK)/2 (or rather the size of the normal stack). On my systems the default soft limit is 8M, a 4M shadow stack supports 512k nested function calls (64bit) - none of which can have any local data. In reality programs that use a lot of stack allocate large buffers on stack, they don't have silly depths of recursive functions with no local data. I've just looked at vmlinux.o - which won't be representative of userspace! While there are a lot of functions with small stack frame (sub $0x10,%rsp) they tend to have saved a few registers in stack first. The majority will have a stack delta of over 64 bytes. That corresponds to rlimit(STACK)/8 and even that is conservative. I'd suspect that could safely halve that again. Actually would it be possible to initially just allocate one page? If you get an overflow fault on the shadow stack I think you can safely reallocate it at an entirely different user virtual address. That would remove all the problems over committing a lot of swap. Most threads will never do the 512 nested calls needed to blow the stack. -- David >=20 >=20 > > -- David > > =20 > > > =20 > > > > But 32bit programs with lots of threads can run out of VA. > > > > Increasing the stack VA size by 50% might even give problems for 64= bit > > > > 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 =20 > > > =20 > > =20