[PATCH v3 5/7] KVM: x86/xen: Explicitly tag "shared info" page as never being dirty tracked

[Woodhouse, David]

From: Sean Christopherson <seanjc@xxxxxxxxxx>

Explicitly mark the Xen shared info page as never being dirty tracked so
that higher-level gpc APIs can be added to automatically take care of
things like dirty tracking, without reintroducing the bug fixed by commit
55749769fe60 ("KVM: x86: Fix wall clock writes in Xen shared_info not to
mark page dirty").  And because the code _looks_ buggy.

No functional change intended.

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        |  2 +-
 include/linux/kvm_host.h  | 10 ++++++++--
 include/linux/kvm_types.h |  1 +
 virt/kvm/pfncache.c       |  4 +++-
 4 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 75fbe88c2102..ff18d888ed47 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -2329,7 +2329,7 @@ void kvm_xen_init_vm(struct kvm *kvm)
 {
 	mutex_init(&kvm->arch.xen.xen_lock);
 	idr_init(&kvm->arch.xen.evtchn_ports);
-	kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm);
+	__kvm_gpc_init(&kvm->arch.xen.shinfo_cache, kvm, true);
 }
 
 void kvm_xen_destroy_vm(struct kvm *kvm)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index da0b3669f1a3..1725284121c9 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1465,7 +1465,13 @@ int kvm_vcpu_write_guest(struct kvm_vcpu *vcpu, gpa_t gpa, const void *data,
  * immutable attributes.  Note, the cache must be zero-allocated (or zeroed by
  * the caller before init).
  */
-void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm);
+void __kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
+		    bool never_dirty);
+
+static inline void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
+{
+	__kvm_gpc_init(gpc, kvm, false);
+}
 
 /**
  * kvm_gpc_activate - prepare a cached kernel mapping and HPA for a given guest
@@ -1974,7 +1980,7 @@ static inline void kvm_gpc_mark_dirty_in_slot(struct gfn_to_pfn_cache *gpc)
 	RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
 			 "kvm_gpc_mark_dirty_in_slot() without RCU read lock");
 
-	if (!gpc->memslot)
+	if (!gpc->memslot || gpc->never_dirty)
 		return;
 
 	mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpa_to_gfn(gpc->gpa));
diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index fdf7d2273298..1ad35ec01f87 100644
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -93,6 +93,7 @@ struct gfn_to_pfn_cache {
 	kvm_pfn_t pfn;
 	bool active;
 	bool valid;
+	bool never_dirty;
 };
 
 #ifdef KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE
diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 3bae4df49165..ffb4e6105344 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -451,7 +451,8 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len)
 	return __kvm_gpc_refresh(gpc, gpc->gpa, uhva);
 }
 
-void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
+void __kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
+		    bool never_dirty)
 {
 	mutex_init(&gpc->refresh_lock);
 
@@ -460,6 +461,7 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm)
 	gpc->gpa = INVALID_GPA;
 	gpc->uhva = KVM_HVA_ERR_BAD;
 	gpc->active = gpc->valid = false;
+	gpc->never_dirty = never_dirty;
 }
 
 static int __kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
-- 
2.43.0

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