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SubjectRe: [PATCH v2] KVM: VMX: Remove redundant handling of bus lock vmexit
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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@google.com>
> Signed-off-by: Hao Xiang <hao.xiang@linux.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.

> + */
> + 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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