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 7EA1CC5DF6D for ; Wed, 19 Aug 2026 10:11:33 +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=R+PPr4LH5JCo56T4OEcpqKtA6FqaZJJQTU/xNmje3fk=; b=iI/NFU/fzbvyjB+fIXZSk7IQCo 0NHxCaAjhiuKs7LkOU++aV36jiq2y9AvgkAUsJbT0sFT2fKqkhc2s4m4QbJxtqaC5KrPMyVyylDjQ HzW6rxOfze6YI8/AbC4cjCI/wBhbn8RVDiyPZY9GrXV8L8271aV7qlZMbKjCIfk9HhnoxxE1Qybjo PEFDLev7xOANT+ipLMCjLzzl4vn3YFyFVXSNVf+e3WSWDOwmivrp9QqK4N4HWylbnkAtXjlvaIvlD b0HsnhHrIZHxy/U8lOKDD3Uovg0kMj2CQj7TbDQ9q6I7zQGvRalKNwFsJA35TdaxS5fF20H1qxplb Fq2sRFzQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wwdGR-00000009UH8-35Pn; Wed, 19 Aug 2026 10:11:19 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wwdGO-00000009UGS-3Vj6 for linux-arm-kernel@lists.infradead.org; Wed, 19 Aug 2026 10:11:18 +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 DB328153B; Wed, 19 Aug 2026 03:11:10 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B44BC3F66F; Wed, 19 Aug 2026 03:11:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1787134274; bh=jm2HpTC8cEcs53XkB4cm7S5Wv9tNGZLKt6fDNOQqogY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sFJe1ZuJ+f8GRxdAgY8srN1RiSC4v2YvCNlLlmUtqGq0JnBUN5kBgYHgAdtl1+WBE 86jkDS1YRlLddNDdfgMKb3RVjJvd/DDlHtSCIqjgjuwU2N63jNz2qDHOX98sxoLboM FHd7s/Mzcrg9P/Q3NGrRDdX07qr9iwtrz3o25+oI= Date: Wed, 19 Aug 2026 11:11:09 +0100 From: Catalin Marinas To: James Houghton Cc: Will Deacon , Muchun Song , Oscar Salvador , Nikos Nikoleris , Linu Cherian , Mark Rutland , David Hildenbrand , Andrew Morton , Ryan Roberts , Nanyong Sun , Yu Zhao , Frank van der Linden , David Rientjes , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH 17/18] arm64: Permit onlining of HVO-incompatible late CPUs if HVO is not in use Message-ID: References: <20260708031129.3503195-1-jthoughton@google.com> <20260708031129.3503195-18-jthoughton@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260708031129.3503195-18-jthoughton@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260819_031117_032545_60834834 X-CRM114-Status: GOOD ( 14.15 ) 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 Wed, Jul 08, 2026 at 03:11:27AM +0000, James Houghton wrote: > First, HVO must have ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU so that > incompatible CPUs can be onlined if HVO is not in use. The > late_cpu_enable() callback is used to check if HVO is truly in use. > > If the late CPU is incompatible with HVO and HVO is *not* in use, HVO > becomes permanently disabled. > > If the late CPU is incompatible with HVO and HVO *is* in use, the CPU > is not onlined. I haven't looked in detail at the logic here but do we actually care about this? We still need to solve the BBML2 requirement around patches 12 and 13. BBML2 won't be an optionally late feature for other reasons, so such CPUs won't be allowed. This leaves us with HW AF. In mainline, the check is done on the sanitised regs but IIRC these can still be overridden on late CPU onlining with a warning. We only use this check as an optimisation, so not an issue in mainline but can be come problematic with HVO. If we don't have a strong use-case for mismatched HAFDBS support, I'd drop these last patches for now. -- Catalin