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SubjectRe: [PATCH v7 3/3] KVM: vmx: handle vm-exit for UMWAIT and TPAUSE
On Fri, Jul 12, 2019 at 04:29:07PM +0800, Tao Xu wrote:
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5213,6 +5213,9 @@ bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
> case EXIT_REASON_ENCLS:
> /* SGX is never exposed to L1 */
> return false;
> + case EXIT_REASON_UMWAIT: case EXIT_REASON_TPAUSE:

Grouped case statements are usually stacked vertically, e.g.:

case EXIT_REASON_UMWAIT:
case EXIT_REASON_TPAUSE:

> + return nested_cpu_has2(vmcs12,
> + SECONDARY_EXEC_ENABLE_USR_WAIT_PAUSE);
> default:
> return true;
> }
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 0787f140d155..e026b1313dc3 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5349,6 +5349,20 @@ static int handle_monitor(struct kvm_vcpu *vcpu)
> return handle_nop(vcpu);
> }
>
> +static int handle_umwait(struct kvm_vcpu *vcpu)
> +{
> + kvm_skip_emulated_instruction(vcpu);
> + WARN(1, "this should never happen\n");

Blech. I'm guessing this code was copy-pasted from handle_xsaves() and
handle_xrstors(). The blurb of "this should never happen" isn't very
helpful, e.g. the WARN itself makes it pretty obvious that we don't expect
to reach this point. WARN_ONCE would also be preferable, no need to spam
the log in the event things go completely haywire.

Rather than propagate ugly code, what about defining a common helper, e.g.

static int handle_unexpected_vmexit(struct kvm_vcpu *vcpu)
{
kvm_skip_emulated_instruction(vcpu);
WARN_ONCE(1, "Unexpected VM-Exit = 0x%x", vmcs_read32(VM_EXIT_REASON));
return 1;
}

...
{
[EXIT_REASON_XSAVES] = handle_unexpected_vmexit,
[EXIT_REASON_XRSTORS] = handle_unexpected_vmexit,

[EXIT_REASON_UMWAIT] = handle_unexpected_vmexit,
[EXIT_REASON_TPAUSE] = handle_unexpected_vmexit,

}

> + return 1;
> +}
> +
> +static int handle_tpause(struct kvm_vcpu *vcpu)
> +{
> + kvm_skip_emulated_instruction(vcpu);
> + WARN(1, "this should never happen\n");
> + return 1;
> +}
> +
> static int handle_invpcid(struct kvm_vcpu *vcpu)
> {
> u32 vmx_instruction_info;
> @@ -5559,6 +5573,8 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
> [EXIT_REASON_VMFUNC] = handle_vmx_instruction,
> [EXIT_REASON_PREEMPTION_TIMER] = handle_preemption_timer,
> [EXIT_REASON_ENCLS] = handle_encls,
> + [EXIT_REASON_UMWAIT] = handle_umwait,
> + [EXIT_REASON_TPAUSE] = handle_tpause,
> };
>
> static const int kvm_vmx_max_exit_handlers =
> --
> 2.20.1
>

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