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 34417CD6E57 for ; Mon, 1 Jun 2026 00:16:45 +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:References:To: From:Subject:Cc:Message-Id:Date:Content-Type:Content-Transfer-Encoding: Mime-Version:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=ZQdZFdRPMl5NqctlRONekKw7Ci+pCu3VSk8zafduNPg=; b=cH0FvBVs4OekOUc3WU+DfMfj1Q 5bepS94Gz0larIi5a7HjljSPioqpNYAkzTgEzRrwZZUPJQLDN+4nPgl9rPdCnsSmu9RFr+FctrhQm QWj73Vad66airW+B4JVBCVc7deVVkdpw8ryCUq0EXGQfbAb1OuYOnwGRGaTqZz4RGVyru34kpr0J7 Yc+FaJV2itvGACtllp7n2NmDSkAxcO0dUVFtp0pegOV3hisntOyrY7oL6FTtEcKgQFBxoMiUw6SXm 5opuHgQ16FFuaFxO7DASJ/pywX6KMLoKHdK62GKxUCCc2zwWsvZBn0JZvfcuSv0f2ZRyDUH4KgpuB FJpG9r+A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wTqKZ-00000009zI9-3m8l; Mon, 01 Jun 2026 00:16:35 +0000 Received: from mail-oa1-x2a.google.com ([2001:4860:4864:20::2a]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wTqKX-00000009zHo-2H3v for linux-arm-kernel@lists.infradead.org; Mon, 01 Jun 2026 00:16:34 +0000 Received: by mail-oa1-x2a.google.com with SMTP id 586e51a60fabf-43bf6230cffso4434410fac.0 for ; Sun, 31 May 2026 17:16:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1780272992; x=1780877792; darn=lists.infradead.org; h=in-reply-to:references:to:from:subject:cc:message-id:date :content-transfer-encoding:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=ZQdZFdRPMl5NqctlRONekKw7Ci+pCu3VSk8zafduNPg=; b=bjTZMoKjoYWk+gpox3vwJLPTn0JKhmKmJ7z58pCdruu98vQpEjDvId6DzpJwulQmXu 5XW7ci3JA4wRL6niCmKq09MliPmGuYqv8j4ddFiY1UDBn/fKfbPjdl/31eaMpF8R3JZd +uw+FiCIJtEq4k40kfkJiSvteKrButH2vdxgoqdRxvavw3rhIO+JpsM5drfUHRQFDOKn V+UgexUTo6pPY/bnlVFJl9NfecRJ6ZNEWMRUC5C1kp4ftvAs25HkxkW+/f6xmhNXVO8z bnvgP1zZyRWKtsSf6TPXbg0xdICjFDtB5kYsqn/FbyLMQ3zJV+97MVIjq0u7XijHiebO neDQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1780272992; x=1780877792; h=in-reply-to:references:to:from:subject:cc:message-id:date :content-transfer-encoding:mime-version:x-gm-gg:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=ZQdZFdRPMl5NqctlRONekKw7Ci+pCu3VSk8zafduNPg=; b=BJmIJ7NZNT2X9lIra/AoJGv4jiHYhQrCMy9YXCdd2KZzmfm3bSaf0FV6I2T2fVKBjp U6oJKfypmZHG92LUb19fjOS7rBlbJa+/GRlJYS+ZXgOQUOspfRuQDw8I+FieNKSFGx37 N38JHvry31wp691EEbF8aVo1oOYjUlEqSDFKAjHC2ExOhC9t3DADiL2iku6wDP23mDc6 Tmvz9Yzvbuf/C/RnEE848pdk9TE4ua4cuFvvpM6joPFQZETCiwpog/Dw0bDgMk5coVTq P8AHywoKA8W9SO7zwLijrsaSdtOK/vNfpo2fx359H47bUczLR0voNxpfKQQCjf7yCWj5 tGhA== X-Forwarded-Encrypted: i=1; AFNElJ9UzokkndgEUxEVFcJy1GJKwQ8x+rWFTczJSB+JFuCGT7eO8vECycKbORminMSobCFcg+ISw4NXlIXGPIdaC0rs@lists.infradead.org X-Gm-Message-State: AOJu0YzC1jNSc3vB5B6rYybwMir79ZbVIMvzbc6Xq5La1nzhllaaWmQW jP2Z6PHwXeJliexnd+TZcCYnRUxP84dZQM2IuzIY199YCfmSHAfP74Lc X-Gm-Gg: Acq92OEsKF4Cfw9qMM2lHUQTRFkPEZzN0Mty+Rp8ktmIFG86Ld9eYumFonTuk2R7AIC i7mrnzrDWwvcCRuYxi5Goq3TTG7NOza7G7vAV4O8ouKSML1nFyyyv1HnP5jSdquBQRP2PVVcyOp TB4qD6b5HttUrQ4HF7x+7L9+SXEksJJTCQYgpr1TBCnfX9FcZ5bbpDac192S/MyvVTYk3agTwsN qaXPtCM5QxnZRyCO2qw61pDZDYkjfeyfm6vEYeIVIGMZYvj+RbqsBv7UEVvrTds9iX7+7I8Uzx9 E8B+PZb5W48OEsOGtlWzhJxod2XB9Lduyi0UXhhn83QK0xOkCS2GBYguMiEjqEs7H3ksGNVNnfF P5WLepCVfmrX6GSlu4Zgfx8L7NIZXxxLfK+Z+2xySr1OpXfY1hq4gAIv+hCbzgvkrHogw+F/ct7 wmsWYxf3QO9a0c4dl04poyapdMhYwf52eklFyF7tolAfsE6PdsLjLMfuU0/vkZgJk9siErRRNB5 8IGyETZAEOFdqcgszY33cfd X-Received: by 2002:a05:6808:80c8:b0:47a:499:b616 with SMTP id 5614622812f47-485fb2aa4c8mr3766450b6e.16.1780272991503; Sun, 31 May 2026 17:16:31 -0700 (PDT) Received: from localhost ([2a03:2880:10ff::]) by smtp.gmail.com with ESMTPSA id 5614622812f47-48605f6a576sm3396395b6e.4.2026.05.31.17.16.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 31 May 2026 17:16:30 -0700 (PDT) Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Sun, 31 May 2026 17:16:27 -0700 Message-Id: Cc: "David Vernet" , "Andrea Righi" , "Changwoo Min" , "Andrii Nakryiko" , "Daniel Borkmann" , "Martin KaFai Lau" , "Kumar Kartikeya Dwivedi" , "Peter Zijlstra" , "Catalin Marinas" , "Will Deacon" , "Thomas Gleixner" , "Ingo Molnar" , "Borislav Petkov" , "Dave Hansen" , "Andrew Morton" , "Mike Rapoport" , "Emil Tsalapatis" , , , , , , Subject: Re: [PATCH 2/8] bpf: Recover arena kernel faults with scratch page From: "Alexei Starovoitov" To: "Tejun Heo" , "Alexei Starovoitov" , "David Hildenbrand" X-Mailer: aerc References: <20260522172219.1423324-1-tj@kernel.org> <20260522172219.1423324-3-tj@kernel.org> <7fd673df-22f3-4d70-a779-ea0b878188b3@kernel.org> <3901fe0537edee9d7acdfd91695ead28@kernel.org> <8cc56c7a4aa29628b7d17d85be7eadb9@kernel.org> In-Reply-To: <8cc56c7a4aa29628b7d17d85be7eadb9@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260531_171633_610594_54D98F4F X-CRM114-Status: GOOD ( 12.12 ) 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 Sun May 31, 2026 at 10:47 AM PDT, Tejun Heo wrote: > Hello, > > I posted the check removal [1], and Sashiko's review flagged a > break-before-make problem with it [2] that I think is real. ohh. interesting. > So instead of just dropping the check, the install should route through a= n > invalid entry rather than overwrite in place: > > while (!ptep_try_set(pte, mk_pte(page, PAGE_KERNEL))) { > old =3D ptep_get(pte); > if (pte_none(old)) > continue; > if (WARN_ON_ONCE(pte_page(old) !=3D arena->scratch_page)) > return -EBUSY; > ptep_get_and_clear(&init_mm, addr, pte); > broke_scratch =3D true; > } > > ptep_try_set() only fills a none slot, so the slot goes scratch->none->pa= ge > and never valid->valid, and the loop copes with a concurrent fault > re-scratching it. This also closes the set_pte_at()-vs-ptep_try_set() rac= e > I raised earlier, since both sides are now cmpxchg. A broken scratch entr= y > was live, so the caller flush_tlb_kernel_range()s those pages when > broke_scratch is set, like arena_free_pages() already does after clearing= . Makes sense to me.