On 7/24/2023 4:26 PM, Chao Gao wrote:
On Thu, Jul 20, 2023 at 11:03:42PM -0400, Yang Weijiang wrote:
+static void kvm_save_cet_supervisor_ssp(struct kvm_vcpu *vcpu)
+{
+ preempt_disable();
what's the purpose of disabling preemption?
Thanks!
These preempt_disable/enable() becomes unnecessary due to the PLx_SSP
handling
in sched_in/out(). Will remove them.
+ if (unlikely(guest_can_use(vcpu, X86_FEATURE_SHSTK))) {
+ rdmsrl(MSR_IA32_PL0_SSP, vcpu->arch.cet_s_ssp[0]);
+ rdmsrl(MSR_IA32_PL1_SSP, vcpu->arch.cet_s_ssp[1]);
+ rdmsrl(MSR_IA32_PL2_SSP, vcpu->arch.cet_s_ssp[2]);
+ /*
+ * Omit reset to host PL{1,2}_SSP because Linux will never use
+ * these MSRs.
+ */
+ wrmsrl(MSR_IA32_PL0_SSP, 0);
You don't need to reset the MSR because current host doesn't enable SSS
and leaving guest value in the MSR won't affect host behavior.
Yes, I just want to make the host PLx_SSPs as clean as possible.
+ }
+ preempt_enable();
+}
+
+static void kvm_reload_cet_supervisor_ssp(struct kvm_vcpu *vcpu)
+{
+ preempt_disable();
+ if (unlikely(guest_can_use(vcpu, X86_FEATURE_SHSTK))) {
+ wrmsrl(MSR_IA32_PL0_SSP, vcpu->arch.cet_s_ssp[0]);
+ wrmsrl(MSR_IA32_PL1_SSP, vcpu->arch.cet_s_ssp[1]);
+ wrmsrl(MSR_IA32_PL2_SSP, vcpu->arch.cet_s_ssp[2]);
+ }
+ preempt_enable();
+}
save/load PLx_SSP in kvm_sched_in/out() and in VCPU_RUN ioctl is sub-optimal.
How about:
1. expose kvm_save/reload_cet_supervisor_ssp()
2. reload guest PLx_SSP in {vmx,svm}_prepare_switch_to_guest()
3. save guest PLx_SSP in vmx_prepare_switch_to_host() and
svm_prepare_host_switch()?
this way existing svm/vmx->guest_state_loaded can help to reduce a lot of
unnecessary PLx_SSP MSR accesses.
Nice suggestion! It looks workable. I'll try this, thanks!
+
int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
{
struct kvm_queued_exception *ex = &vcpu->arch.exception;
@@ -11222,6 +11249,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
kvm_sigset_activate(vcpu);
kvm_run->flags = 0;
kvm_load_guest_fpu(vcpu);
+ kvm_reload_cet_supervisor_ssp(vcpu);
kvm_vcpu_srcu_read_lock(vcpu);
if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
@@ -11310,6 +11338,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
r = vcpu_run(vcpu);
out:
+ kvm_save_cet_supervisor_ssp(vcpu);
kvm_put_guest_fpu(vcpu);
if (kvm_run->kvm_valid_regs)
store_regs(vcpu);
@@ -12398,9 +12427,17 @@ void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
pmu->need_cleanup = true;
kvm_make_request(KVM_REQ_PMU, vcpu);
}
+
+ kvm_reload_cet_supervisor_ssp(vcpu);
+
static_call(kvm_x86_sched_in)(vcpu, cpu);
}
+void kvm_arch_sched_out(struct kvm_vcpu *vcpu, int cpu)
+{
@cpu its meaning isn't clear and isn't used and ...
Yes, I should have removed it.
+ kvm_save_cet_supervisor_ssp(vcpu);
+}
+
void kvm_arch_free_vm(struct kvm *kvm)
{
kfree(to_kvm_hv(kvm)->hv_pa_pg);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index d90331f16db1..b3032a5f0641 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1423,6 +1423,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu);
void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu);
+void kvm_arch_sched_out(struct kvm_vcpu *vcpu, int cpu);
void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 66c1447d3c7f..42f28e8905e1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -5885,6 +5885,7 @@ static void kvm_sched_out(struct preempt_notifier *pn,
{
struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
+ kvm_arch_sched_out(vcpu, 0);
passing 0 always looks problematic.
Can you elaborate? I have no intent to use @cpu now.
if (current->on_rq) {
WRITE_ONCE(vcpu->preempted, true);
WRITE_ONCE(vcpu->ready, true);
--
2.27.0
