Re: [PATCH v16 19/51] KVM: x86: Don't emulate task switches when IBT or SHSTK is enabled

Sean Christopherson
2025-09-22T17:23:55Z

On Mon, Sep 22, 2025, Binbin Wu wrote:
>
>
> On 9/20/2025 6:32 AM, Sean Christopherson wrote:
> > Exit to userspace with KVM_INTERNAL_ERROR_EMULATION if the guest triggers
> > task switch emulation with Indirect Branch Tracking or Shadow Stacks
> > enabled,
>
> The code just does it when shadow stack is enabled.

Doh. Fixed that and the EMULATION_FAILED typo Chao pointed out:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8b31dfcb1de9..06a88a2b08d7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12194,9 +12194,9 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
*/
if (__kvm_emulate_msr_read(vcpu, MSR_IA32_U_CET, &u_cet) ||
__kvm_emulate_msr_read(vcpu, MSR_IA32_S_CET, &s_cet))
- return EMULATION_FAILED;
+ goto unhandled_task_switch;

- if ((u_cet | s_cet) & CET_SHSTK_EN)
+ if ((u_cet | s_cet) & (CET_ENDBR_EN | CET_SHSTK_EN))
goto unhandled_task_switch;
}