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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5D7FDCCF9EA for ; Mon, 27 Oct 2025 13:32:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 68EE880053; Mon, 27 Oct 2025 09:32:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 63F578000A; Mon, 27 Oct 2025 09:32:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 57C7B80053; Mon, 27 Oct 2025 09:32:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 422748000A for ; Mon, 27 Oct 2025 09:32:56 -0400 (EDT) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id D7EB0C0115 for ; Mon, 27 Oct 2025 13:32:55 +0000 (UTC) X-FDA: 84043984710.08.84F4732 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf12.hostedemail.com (Postfix) with ESMTP id AFDEA40009 for ; Mon, 27 Oct 2025 13:32:53 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=none; spf=pass (imf12.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1761571974; a=rsa-sha256; cv=none; b=KF3jgWVvDg15NJVLMw4r62PQ5H5bwfnxWRjU5Q95wRNWflV0AXGUFF6P/pJ9V77LLKUdM3 /c1uw/p4ErCHcMQxpM6AF4fQmEK8u1VOt6bA1G+PMoJ4nUpi2zjSNVjXdBvVynX+J5qFZp OKrxZJCaRdqn0z6lpXBlUCRc3CjPD7s= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=none; spf=pass (imf12.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1761571974; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=LZIV7DiVBQ9ZGj7Mw+AxaUbETtcLCEViFbmC0IEP6UQ=; b=tlicdbbd3nIn2fz6s5ojqJElbWzn/Ub7R9+98SN3X7IJv/+plLukxsg+GvP0WRDaAgOZVQ 49qH4PIZ4Ow+S1ZRvkEKETJdcudTy0/E4orcqaMSiS0mbqIRHh7VCNbt6MFqj959W099xE 4/Azn6791rMR9p2UKR8K6EJcmMY0FCw= 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 A1A07175D; Mon, 27 Oct 2025 06:32:44 -0700 (PDT) Received: from [10.57.68.196] (unknown [10.57.68.196]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AF5AF3F673; Mon, 27 Oct 2025 06:32:45 -0700 (PDT) Message-ID: <2be0732d-d8fb-424d-bc4e-443cc49d0092@arm.com> Date: Mon, 27 Oct 2025 14:32:42 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 11/13] x86/xen: use lazy_mmu_state when context-switching To: David Hildenbrand , Demi Marie Obenour , David Woodhouse , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , "David S. Miller" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Ryan Roberts , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org References: <20251015082727.2395128-1-kevin.brodsky@arm.com> <20251015082727.2395128-12-kevin.brodsky@arm.com> <348e5f1c5a90e4ab0f14b4d997baf7169745bf04.camel@infradead.org> <70723f4a-f42b-4d94-9344-5824e48bfad1@redhat.com> <3ff4aaeb-61ce-4b72-ba90-1b66374b1b95@gmail.com> <6c9bd0c6-0968-41ac-b0b4-53c881748cfb@redhat.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: <6c9bd0c6-0968-41ac-b0b4-53c881748cfb@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: zoh9up55ue7djoohotj7s5h5rngigf9f X-Rspamd-Queue-Id: AFDEA40009 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1761571973-556025 X-HE-Meta: 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 Fxhx426F MvagrmZwxsSCuOAhGFykJMocfzMbh/MdZipx4SY8pQTeYsGuxH9Z1oYGO4ibwiauMPILjIe3fYH79eyjqI8ibAyL6z4bFzDgrrcJMSA9UdisBYjTt8ZQZQVRvt1mB50Iw5n1rWtFNWIsk5DH/B10ls1FmlHvOKatdZsy38Ay9Ej5av9cpZyd790PvsCBZfOxZ+lUzXn1gdZd84Ap81Gi/16j9ZyIzsJXRNNd557zNCNJi311vBQ0HC4VJnCVy5kh3D57AArHj/knsMg94UbfyMj3oyg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27/10/2025 13:29, David Hildenbrand wrote: > On 25.10.25 00:52, Demi Marie Obenour wrote: >> On 10/24/25 10:51, David Hildenbrand wrote: >>> On 24.10.25 16:47, David Woodhouse wrote: >>>> On Thu, 2025-10-23 at 22:06 +0200, David Hildenbrand wrote: >>>>> On 15.10.25 10:27, Kevin Brodsky wrote: >>>>>> We currently set a TIF flag when scheduling out a task that is in >>>>>> lazy MMU mode, in order to restore it when the task is scheduled >>>>>> again. >>>>>> >>>>>> The generic lazy_mmu layer now tracks whether a task is in lazy MMU >>>>>> mode in task_struct::lazy_mmu_state. We can therefore check that >>>>>> state when switching to the new task, instead of using a separate >>>>>> TIF flag. >>>>>> >>>>>> Signed-off-by: Kevin Brodsky >>>>>> --- >>>>> >>>>> >>>>> Looks ok to me, but I hope we get some confirmation from x86 / xen >>>>> folks. >>>> >>>> >>>> I know tglx has shouted at me in the past for precisely this reminder, >>>> but you know you can test Xen guests under QEMU/KVM now and don't need >>>> to actually run Xen? Has this been boot tested? >>> >>> And after that, boot-testing sparc as well? :D >>> >>> If it's easy, why not. But other people should not suffer for all the >>> XEN hacks we keep dragging along. >> >> Which hacks?  Serious question.  Is this just for Xen PV or is HVM >> also affected? > > In the context of this series, XEN_LAZY_MMU. FWIW in that particular case it's relatively easy to tell this is specific to Xen PV (this is only used in mmu_pv.c and enlighten_pv.c). Knowing what to test is certainly not obvious in general, though. - Kevin > > Your question regarding PV/HVM emphasizes my point: how is a submitter > supposed to know which XEN combinations to test (and how to test > them), to not confidentially break something here. > > We really need guidance+help from the XEN folks here.