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Date: Fri, 15 Oct 2021 16:43:40 +0800 From: Xiaoyao Li <xiaoyao.li@...el.com> To: Hao Xiang <hao.xiang@...ux.alibaba.com>, kvm@...r.kernel.org Cc: shannon.zhao@...ux.alibaba.com, pbonzini@...hat.com, linux-kernel@...r.kernel.org, seanjc@...gle.com Subject: Re: [PATCH v2] KVM: VMX: Remove redundant handling of bus lock vmexit On 10/15/2021 3:28 PM, Hao Xiang wrote: > > > On 2021/10/15 14:46, Xiaoyao Li wrote: >> On 10/15/2021 11:57 AM, Hao Xiang wrote: >>> Hardware may or may not set exit_reason.bus_lock_detected on BUS_LOCK >>> VM-Exits. Dealing with KVM_RUN_X86_BUS_LOCK in handle_bus_lock_vmexit >>> could be redundant when exit_reason.basic is EXIT_REASON_BUS_LOCK. >>> >>> We can remove redundant handling of bus lock vmexit. Force Setting >>> exit_reason.bus_lock_detected in handle_bus_lock_vmexit(), and deal with >>> KVM_RUN_X86_BUS_LOCK only in vmx_handle_exit(). >>> >>> Suggested-by: Sean Christopherson <seanjc@...gle.com> >>> Signed-off-by: Hao Xiang <hao.xiang@...ux.alibaba.com> >>> --- >>> v1 -> v2: a little modifications of comments >>> >>> arch/x86/kvm/vmx/vmx.c | 15 +++++++++------ >>> 1 file changed, 9 insertions(+), 6 deletions(-) >>> >>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c >>> index 116b089..22be02e 100644 >>> --- a/arch/x86/kvm/vmx/vmx.c >>> +++ b/arch/x86/kvm/vmx/vmx.c >>> @@ -5562,9 +5562,13 @@ static int handle_encls(struct kvm_vcpu *vcpu) >>> static int handle_bus_lock_vmexit(struct kvm_vcpu *vcpu) >>> { >>> - vcpu->run->exit_reason = KVM_EXIT_X86_BUS_LOCK; >>> - vcpu->run->flags |= KVM_RUN_X86_BUS_LOCK; >>> - return 0; >>> + /* >>> + * Hardware may or may not set the BUS_LOCK_DETECTED flag on >>> BUS_LOCK >>> + * VM-Exits, force setting the flag >> >>> so that the logic in vmx_handle_exit() >>> + * doesn't have to handle the flag and the basic exit reason. >> >> The code itself looks good. >> >> But the comment is partly incorrect. Now we rely only on the >> bus_lock_detected flag so vmx_handle_exit() must check the flag. >> Thank you for you advice. Is the following comment ok? > /* > * Hardware may or may not set the BUS_LOCK_DETECTED flag on BUS_LOCK > * VM-Exits. Forcely set the flag here, then check the flag in > * vmx_handle_exit() and handle the bus lock vmexit if the flag is > * set. > */ (I'm not sure if forcely is a valid word) how about /* * Hardware may or may not set the BUS_LOCK_DETECTED flag on BUS_LOCK * VM Exit. Unconditionally set the flag here and leave the handling to * vmx_handle_exit(). */ >>> + */ >>> + to_vmx(vcpu)->exit_reason.bus_lock_detected = true; >>> + return 1; >>> } >>> /* >>> @@ -6051,9 +6055,8 @@ static int vmx_handle_exit(struct kvm_vcpu >>> *vcpu, fastpath_t exit_fastpath) >>> int ret = __vmx_handle_exit(vcpu, exit_fastpath); >>> /* >>> - * Even when current exit reason is handled by KVM internally, we >>> - * still need to exit to user space when bus lock detected to >>> inform >>> - * that there is a bus lock in guest. >>> + * 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 (ret > 0) >>>
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