[PATCH 2/6] KVM: nSVM: Add CLASS()es for automagically handling local kvm_vcpu_map() usage

[Sean Christopherson <seanjc@google.com>]

Add CLASS() definitions for locally mapping a PFN using kvm_vcpu_map()
given a vCPU+gfn pair.  In addition to eliminating the need to manually
do unmap(), e.g. in error paths, this will allow hardening KVM against
double-mapping without having to manually ensure every on-stack declaration
is zero-initialized.

Use "map local" as the primary terminology as the basic concept is more or
less the same as kmap_local(): ensure the current context has a kernel
mapping to the underlying memory.

Immediately convert the relatively straightforward nested SVM flows, and
defer converting the more involved SMM flows to a separate change.

No functional change intended.

Cc: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/nested.c | 18 +++++++-----------
 arch/x86/kvm/svm/svm.c    |  8 +++-----
 include/linux/kvm_host.h  | 19 +++++++++++++++++++
 3 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 5e3e280cd483..73f37b050d0a 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1086,14 +1086,14 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa, bool from_vmrun)
 static int nested_svm_copy_vmcb12_to_cache(struct kvm_vcpu *vcpu, u64 vmcb12_gpa)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
-	struct kvm_host_map map;
 	struct vmcb *vmcb12;
 	int r = 0;
 
-	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map))
+	CLASS(kvm_vcpu_map_local, m)(vcpu, gpa_to_gfn(vmcb12_gpa));
+	if (m.ret)
 		return -EFAULT;
 
-	vmcb12 = map.hva;
+	vmcb12 = m.map.hva;
 	nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
 	nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
 
@@ -1107,7 +1107,6 @@ static int nested_svm_copy_vmcb12_to_cache(struct kvm_vcpu *vcpu, u64 vmcb12_gpa
 		r = -EINVAL;
 	}
 
-	kvm_vcpu_unmap(vcpu, &map);
 	return r;
 }
 
@@ -1251,15 +1250,13 @@ static int nested_svm_vmexit_update_vmcb12(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 	struct vmcb *vmcb02 = svm->nested.vmcb02.ptr;
-	struct kvm_host_map map;
 	struct vmcb *vmcb12;
-	int rc;
 
-	rc = kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa), &map);
-	if (rc)
-		return rc;
+	CLASS(kvm_vcpu_map_local, m)(vcpu, gpa_to_gfn(svm->nested.vmcb12_gpa));
+	if (m.ret)
+		return m.ret;
 
-	vmcb12 = map.hva;
+	vmcb12 = m.map.hva;
 
 	vmcb12->save.es     = vmcb02->save.es;
 	vmcb12->save.cs     = vmcb02->save.cs;
@@ -1314,7 +1311,6 @@ static int nested_svm_vmexit_update_vmcb12(struct kvm_vcpu *vcpu)
 				       vmcb12->control.exit_int_info_err,
 				       KVM_ISA_SVM);
 
-	kvm_vcpu_unmap(vcpu, &map);
 	return 0;
 }
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 91286d46d13a..bf10483c0e8a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2216,7 +2216,6 @@ static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
 	u64 vmcb12_gpa = kvm_rax_read(vcpu);
 	struct vcpu_svm *svm = to_svm(vcpu);
 	struct vmcb *vmcb12;
-	struct kvm_host_map map;
 	int ret;
 
 	if (nested_svm_check_permissions(vcpu))
@@ -2227,10 +2226,11 @@ static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
 		return 1;
 	}
 
-	if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcb12_gpa), &map))
+	CLASS(kvm_vcpu_map_local, m)(vcpu, gpa_to_gfn(vmcb12_gpa));
+	if (m.ret)
 		return kvm_handle_memory_failure(vcpu, X86EMUL_IO_NEEDED, NULL);
 
-	vmcb12 = map.hva;
+	vmcb12 = m.map.hva;
 
 	ret = kvm_skip_emulated_instruction(vcpu);
 
@@ -2243,8 +2243,6 @@ static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
 		svm_copy_vmloadsave_state(vmcb12, svm->vmcb01.ptr);
 	}
 
-	kvm_vcpu_unmap(vcpu, &map);
-
 	return ret;
 }
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9db6eb4023c4..c54dbfdbc346 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1420,6 +1420,25 @@ static inline void kvm_vcpu_map_mark_dirty(struct kvm_vcpu *vcpu,
 		kvm_vcpu_mark_page_dirty(vcpu, map->gfn);
 }
 
+typedef struct {
+	struct kvm_vcpu *vcpu;
+	struct kvm_host_map map;
+	int ret;
+} kvm_vcpu_local_map_t;
+
+#define DEFINE_VCPU_MAP_CLASS(ro)					\
+DEFINE_CLASS(kvm_vcpu_map_local##ro, kvm_vcpu_local_map_t,		\
+	     if (!_T.ret) kvm_vcpu_unmap(_T.vcpu, &_T.map),		\
+	     ({								\
+		kvm_vcpu_local_map_t m = { .vcpu = vcpu };		\
+									\
+		m.ret = kvm_vcpu_map##ro(vcpu, gfn, &m.map);		\
+									\
+		m;							\
+	     }), struct kvm_vcpu *vcpu, gfn_t gfn);
+DEFINE_VCPU_MAP_CLASS();
+DEFINE_VCPU_MAP_CLASS(_readonly);
+
 unsigned long kvm_vcpu_gfn_to_hva(struct kvm_vcpu *vcpu, gfn_t gfn);
 unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *writable);
 int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, int offset,
-- 
2.55.0.229.g6434b31f56-goog