From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tomoki Sekiyama Subject: Re: [RFC PATCH 16/18] KVM: add kvm_arch_vcpu_prevent_run to prevent VM ENTER when NMI is received Date: Fri, 29 Jun 2012 18:26:17 +0900 Message-ID: <4FED74B9.3020308@hitachi.com> References: <20120628060719.19298.43879.stgit@localhost.localdomain> <20120628060842.19298.14653.stgit@localhost.localdomain> <4FEC8AFB.8060606@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, yrl.pp-manager.tt@hitachi.com, mtosatti@redhat.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com To: avi@redhat.com Return-path: In-Reply-To: <4FEC8AFB.8060606@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 2012/06/29 1:48, Avi Kivity wrote: > On 06/28/2012 09:08 AM, Tomoki Sekiyama wrote: >> Since NMI can not be disabled around VM enter, there is a race between >> receiving NMI to kick a guest and entering the guests on slave CPUs.If the >> NMI is received just before entering VM, after the NMI handler is invoked, >> it continues entering the guest and the effect of the NMI will be lost. >> >> This patch adds kvm_arch_vcpu_prevent_run(), which causes VM exit right >> after VM enter. The NMI handler uses this to ensure the execution of the >> guest is cancelled after NMI. >> >> >> +/* >> + * Make VMRESUME fail using preemption timer with timer value = 0. >> + * On processors that doesn't support preemption timer, VMRESUME will fail >> + * by internal error. >> + */ >> +static void vmx_prevent_run(struct kvm_vcpu *vcpu, int prevent) >> +{ >> + if (prevent) >> + vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL, >> + PIN_BASED_PREEMPTION_TIMER); >> + else >> + vmcs_clear_bits(PIN_BASED_VM_EXEC_CONTROL, >> + PIN_BASED_PREEMPTION_TIMER); >> +} > > This may interrupt another RMW sequence, which will then overwrite the > control. So it needs to be called only if inside the entry sequence > (otherwise can just set a KVM_REQ_IMMEDIATE_EXIT in vcpu->requests). > I agree. I will add the check whether it is in the entry sequence. Thanks, -- Tomoki Sekiyama Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory