[PATCH v4 4/6] KVM: x86/xen: Don't dirty track "vCPU info" page

[David Woodhouse]

From: Sean Christopherson <seanjc@xxxxxxxxxx>

Give the Xen per-vCPU info page the same treatment as the per-VM shared
info page, and never mark it dirty, as KVM clearly relies on userspace to
assume the page is always dirty.  While the page is marked dirty on writes
via kvm_xen_inject_pending_events(), it's not marked dirty when written by
__kvm_xen_set_evtchn_fast().

Furthermore, as was the case with the shared info page, writes in the event
channel fastpath may be done without an active vCPU, e.g. when called via
timer callback or irqfd injection.  I.e. attempting to fix the fastpath
would run afoul of the same issue that was fixed by commit 55749769fe60
("KVM: x86: Fix wall clock writes in Xen shared_info not to mark page
dirty").

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Assisted-by: Claude:claude-mythos-5
---
 arch/x86/kvm/xen.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index fab215a522be..5618e2ccf4c4 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -666,7 +666,6 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
 		WRITE_ONCE(vi->evtchn_upcall_pending, 1);
 	}
 
-	kvm_gpc_mark_dirty_in_slot(gpc);
 	srcu_read_unlock(&v->kvm->gpc_srcu, idx);
 
 	/* For the per-vCPU lapic vector, deliver it as MSI. */
@@ -2375,7 +2374,7 @@ void kvm_xen_init_vcpu(struct kvm_vcpu *vcpu)
 
 	kvm_gpc_init(&vcpu->arch.xen.runstate_cache, vcpu->kvm);
 	kvm_gpc_init(&vcpu->arch.xen.runstate2_cache, vcpu->kvm);
-	kvm_gpc_init(&vcpu->arch.xen.vcpu_info_cache, vcpu->kvm);
+	__kvm_gpc_init(&vcpu->arch.xen.vcpu_info_cache, vcpu->kvm, true);
 	kvm_gpc_init(&vcpu->arch.xen.vcpu_time_info_cache, vcpu->kvm);
 }
 
-- 
2.55.0