Re: [PATCH v19 093/130] KVM: TDX: Implements vcpu request_immediate_exit

Chao Gao
2024-03-29T01:54:18Z

On Mon, Feb 26, 2024 at 12:26:35AM -0800, isaku.yamahata@intel.com wrote:
>From: Isaku Yamahata <isaku.yamahata@intel.com>
>
>Now we are able to inject interrupts into TDX vcpu, it's ready to block TDX
>vcpu. Wire up kvm x86 methods for blocking/unblocking vcpu for TDX. To
>unblock on pending events, request immediate exit methods is also needed.

TDX doesn't support this immediate exit. It is considered as a potential
attack to TDs. TDX module deploys 0/1-step mitigations to prevent this.
Even KVM issues a self-IPI before TD-entry, TD-exit will happen after
the guest runs a random number of instructions.

KVM shouldn't request immediate exits in the first place. Just emit a
warning if KVM tries to do this.

>
>Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
>Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
>---
> arch/x86/kvm/vmx/main.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
>index f2c9d6358f9e..ee6c04959d4c 100644
>--- a/arch/x86/kvm/vmx/main.c
>+++ b/arch/x86/kvm/vmx/main.c
>@@ -372,6 +372,16 @@ static void vt_enable_irq_window(struct kvm_vcpu *vcpu)
> vmx_enable_irq_window(vcpu);
> }
>
>+static void vt_request_immediate_exit(struct kvm_vcpu *vcpu)
>+{
>+ if (is_td_vcpu(vcpu)) {
>+ __kvm_request_immediate_exit(vcpu);
>+ return;
>+ }
>+
>+ vmx_request_immediate_exit(vcpu);
>+}
>+
> static u8 vt_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> {
> if (is_td_vcpu(vcpu))
>@@ -549,7 +559,7 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
> .check_intercept = vmx_check_intercept,
> .handle_exit_irqoff = vmx_handle_exit_irqoff,
>
>- .request_immediate_exit = vmx_request_immediate_exit,
>+ .request_immediate_exit = vt_request_immediate_exit,
>
> .sched_in = vt_sched_in,
>
>--
>2.25.1
>
>