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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id c24-20020a17090abf1800b001cd4989ff44sm1408334pjs.11.2022.05.03.07.17.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 May 2022 07:17:57 -0700 (PDT) Date: Tue, 3 May 2022 14:17:53 +0000 From: Sean Christopherson To: Seth Forshee 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: <20220503125729.2556498-1-sforshee@digitalocean.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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... > + * 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(). > kvm_handle_signal_exit(vcpu); > return -EINTR; > } > -- > 2.32.0 >