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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 56A6BC433EF for ; Tue, 3 May 2022 16:18:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239321AbiECQVi (ORCPT ); Tue, 3 May 2022 12:21:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60902 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239313AbiECQVh (ORCPT ); Tue, 3 May 2022 12:21:37 -0400 Received: from mail-oi1-x234.google.com (mail-oi1-x234.google.com [IPv6:2607:f8b0:4864:20::234]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B28502ED78 for ; Tue, 3 May 2022 09:18:04 -0700 (PDT) Received: by mail-oi1-x234.google.com with SMTP id m11so18640884oib.11 for ; Tue, 03 May 2022 09:18:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=digitalocean.com; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Q51Ia3tetkXHUbkcfKD8S+gdtewHxa7+IUzoOiuzmQM=; b=DXNemHdAsSJnzRfAFmFJDu7rxBi3j2CgdmhDiTTYFUQVZd81cb6Uc+goqkxzhoaGaE rc1WCcIRmRkCpMkO0bJFB3uqZkeysudG4ESGLjj/ionJPTbCH6O/8VdViXZbrD2f4QEs 3SJHX2OkoKRviER0B91sBk/C0juHWnWJQLLHU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Q51Ia3tetkXHUbkcfKD8S+gdtewHxa7+IUzoOiuzmQM=; b=GIKDWegFcrx1NqoEpLMvgiPGKAaJyGvRk7mST1PXc2+4clGlj0IPqzl+RgSUcCPCwA Jm+xLrftukBduDkMCyJKbEEO4JZd/txL8oZcNHnhbF7Z/6NqlmuCqaOnpfODrQLXyUgk wRxT11cCWta3I2YAqBiFO9P09kvJxqPg53p54gX+2kQHPJWuTS7B8zD7Iqr9offQa9PY TdeRSrMV664hMLeArVCQtlqCHzpMpiHZSGbgMlq2wJ3TfJa8DfI7Zq7nrQh28osN8u42 sLZnlghgW15PA8add1AQehpVbEb30sgpYe8s5r7rJIvfHjVL9DKUEI6yOdnG8ciCF4US qrkA== X-Gm-Message-State: AOAM531qNdaixQnIyz4K1VkCRS88qPkJS1jYK4Jl+1dOibzRgX8WV3kG ICiqmkXahlmrOqnk3/a9RQy2hA== X-Google-Smtp-Source: ABdhPJzaqQPI/1igl+iB0OUCnACAJFry6dBnUhBprcHogtJiHS4VmyVxX1E5pHmdYanKyutyiI/1rA== X-Received: by 2002:a05:6808:1202:b0:322:dc37:2c3b with SMTP id a2-20020a056808120200b00322dc372c3bmr2217794oil.298.1651594683941; Tue, 03 May 2022 09:18:03 -0700 (PDT) Received: from localhost ([2605:a601:ac0f:820:80d8:f53c:c84d:deaa]) by smtp.gmail.com with ESMTPSA id 8-20020a056870124800b000e686d13888sm7369543oao.34.2022.05.03.09.18.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 May 2022 09:18:03 -0700 (PDT) Date: Tue, 3 May 2022 11:18:02 -0500 From: Seth Forshee To: Sean Christopherson Cc: Thomas Gleixner , Peter Zijlstra , Andy Lutomirski , Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , Paolo Bonzini , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH] entry/kvm: Make vCPU tasks exit to userspace when a livepatch is pending Message-ID: References: <20220503125729.2556498-1-sforshee@digitalocean.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Tue, May 03, 2022 at 02:17:53PM +0000, Sean Christopherson wrote: > On Tue, May 03, 2022, Seth Forshee wrote: > > A livepatch migration for a task can only happen when the task is > > sleeping or it exits to userspace. This may happen infrequently for a > > heavily loaded vCPU task, leading to livepatch transition failures. > > > > Fake signals will be sent to tasks which fail to migrate via stack > > checking. This will cause running vCPU tasks to exit guest mode, but > > since no signal is pending they return to guest execution without > > exiting to userspace. Fix this by treating a pending livepatch migration > > like a pending signal, exiting to userspace with EINTR. This allows the > > migration to complete, and userspace should re-excecute KVM_RUN to > > resume guest execution. > > > > In my testing, systems where livepatching would timeout after 60 seconds > > were able to load livepatches within a couple of seconds with this > > change. > > > > Signed-off-by: Seth Forshee > > --- > > kernel/entry/kvm.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/entry/kvm.c b/kernel/entry/kvm.c > > index 9d09f489b60e..efe4b791c253 100644 > > --- a/kernel/entry/kvm.c > > +++ b/kernel/entry/kvm.c > > @@ -14,7 +14,12 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work) > > task_work_run(); > > } > > > > - if (ti_work & _TIF_SIGPENDING) { > > + /* > > + * When a livepatch migration is pending, force an exit to > > Can the changelog and comment use terminology other than migration? Maybe "transition"? > That seems to be prevelant through the livepatch code and docs. There are already > too many meanings for "migration" in KVM, e.g. live migration, page migration, task/vCPU > migration, etc... "Transition" is used a lot, but afaict it refers to the overall state of the livepatch. "Migrate" is used a lot less, but it always seems to refer to patching a single task, which is why I used that term. But I can see the opportunity for confusion, so I'll reword it. > > > + * userspace as though a signal is pending to allow the > > + * migration to complete. > > + */ > > + if (ti_work & (_TIF_SIGPENDING | _TIF_PATCH_PENDING)) { > > _TIF_PATCH_PENDING needs to be in XFER_TO_GUEST_MODE_WORK too, otherwise there's > no guarantee KVM will see the flag and invoke xfer_to_guest_mode_handle_work(). Yes, you are right. I was relying on the livepatch code setting _TIF_NOTIFY_SIGNAL for vCPU tasks which were running, but it would be better to have _TIF_PATCH_PENDING in XFER_TO_GUEST_MODE_WORK too. Thanks, Seth > > > kvm_handle_signal_exit(vcpu); > > return -EINTR; > > } > > -- > > 2.32.0 > >