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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id lb20sm799141ejc.40.2021.09.22.03.02.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Sep 2021 03:02:44 -0700 (PDT) Subject: Re: [PATCH] KVM: VMX: Check if bus lock vmexit was preempted To: Hao Xiang , kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, chenyi.qiang@intel.com, sean.j.christopherson@intel.com, shannon.zhao@linux.alibaba.com References: <1631964600-73707-1-git-send-email-hao.xiang@linux.alibaba.com> From: Paolo Bonzini Message-ID: <87b411c3-da75-e074-91a4-a73891f9f5f8@redhat.com> Date: Wed, 22 Sep 2021 12:02:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <1631964600-73707-1-git-send-email-hao.xiang@linux.alibaba.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/09/21 13:30, Hao Xiang wrote: > exit_reason.bus_lock_detected is not only set when bus lock VM exit > was preempted, in fact, this bit is always set if bus locks are > detected no matter what the exit_reason.basic is. > > So the bus_lock_vmexit handling in vmx_handle_exit should be duplicated > when exit_reason.basic is EXIT_REASON_BUS_LOCK(74). We can avoid it by > checking if bus lock vmexit was preempted in vmx_handle_exit. I don't understand, does this mean that bus_lock_detected=1 if basic=EXIT_REASON_BUS_LOCK? If so, can we instead replace the contents of handle_bus_lock_vmexit with /* Do nothing and let vmx_handle_exit exit to userspace. */ WARN_ON(!to_vmx(vcpu)->exit_reason.bus_lock_detected); return 0; ? That would be doable only if this is architectural behavior and not a processor erratum, of course. Thanks, Paolo > Signed-off-by: Hao Xiang > --- > arch/x86/kvm/vmx/vmx.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index 0c2c0d5..5ddf1df 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -6054,7 +6054,8 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath) > * still need to exit to user space when bus lock detected to inform > * that there is a bus lock in guest. > */ > - if (to_vmx(vcpu)->exit_reason.bus_lock_detected) { > + if (to_vmx(vcpu)->exit_reason.bus_lock_detected && > + to_vmx(vcpu)->exit_reason.basic != EXIT_REASON_BUS_LOCK) { > if (ret > 0) > vcpu->run->exit_reason = KVM_EXIT_X86_BUS_LOCK; > >