[PATCH 5.15.y 2/2] KVM: x86: Fill kvm_run exit fields in common get_nested_state_pages() error paths

[Sasha Levin <sashal@kernel.org>]

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit c1214f293d77c6e425a379f90d09bdb4815993a8 ]

Fill kvm_run with "internal error, emulation" in the common error handling
paths for getting nested state pages, as requiring each check to manually
fill kvm_run is error prone and requires a non-trivial amount of copy+paste.

Specifically, both SVM and VMX fail to fill kvm_run if load_pdptrs() fails,
and SVM fails to fill kvm_run if kvm_hv_verify_vp_assist() fails.  If those
flows fail, the *best* case scenario is that KVM will exit to userspace
with KVM_EXIT_UNKNOWN.  The worst case scenario is that KVM exits with a
stale exit_reason and confuses userspace.

Note, SVM never exits to userspace if something goes sideways when dealing
with vmcb12 assets while emulating VMRUN, i.e. lack of SVM-specific code is
not a bug.

Fixes: 0f85722341b0 ("KVM: nVMX: delay loading of PDPTRs to KVM_REQ_GET_NESTED_STATE_PAGES")
Fixes: 232f75d3b4b5 ("KVM: nSVM: call nested_svm_load_cr3 on nested state load")
Fixes: 3f4a812edf5c ("KVM: nSVM: hyper-v: Enable L2 TLB flush")
Cc: stable@vger.kernel.org
Reported-by: Jinwoo Lee <rkskek9254@gmail.com>
Closes: https://lore.kernel.org/all/20260813043932.3214460-1-rkskek9254@gmail.com
Reported-by: Stefan Teodorescu <fane@google.com>
Link: https://patch.msgid.link/20260921211608.1030158-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/svm/nested.c |  7 +------
 arch/x86/kvm/vmx/nested.c | 15 +++++----------
 arch/x86/kvm/x86.c        |  3 +++
 3 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 08f30b5ebe30f..7b3f0d506a986 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1439,13 +1439,8 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
 		if (CC(!load_pdptrs(vcpu, vcpu->arch.walk_mmu, vcpu->arch.cr3)))
 			return false;
 
-	if (!nested_svm_merge_msrpm(vcpu)) {
-		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-		vcpu->run->internal.suberror =
-			KVM_INTERNAL_ERROR_EMULATION;
-		vcpu->run->internal.ndata = 0;
+	if (!nested_svm_merge_msrpm(vcpu))
 		return false;
-	}
 
 	return true;
 }
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 1b87dded131dc..dbd16e08da396 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3222,10 +3222,6 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 		} else {
 			pr_debug_ratelimited("%s: no backing 'struct page' for APIC-access address in vmcs12\n",
 					     __func__);
-			vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-			vcpu->run->internal.suberror =
-				KVM_INTERNAL_ERROR_EMULATION;
-			vcpu->run->internal.ndata = 0;
 			return false;
 		}
 	}
@@ -3289,11 +3285,6 @@ static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
 	if (!nested_get_evmcs_page(vcpu)) {
 		pr_debug_ratelimited("%s: enlightened vmptrld failed\n",
 				     __func__);
-		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-		vcpu->run->internal.suberror =
-			KVM_INTERNAL_ERROR_EMULATION;
-		vcpu->run->internal.ndata = 0;
-
 		return false;
 	}
 
@@ -3681,8 +3672,12 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 
 vmentry_failed:
 	vcpu->arch.nested_run_pending = 0;
-	if (status == NVMX_VMENTRY_KVM_INTERNAL_ERROR)
+	if (status == NVMX_VMENTRY_KVM_INTERNAL_ERROR) {
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+		vcpu->run->internal.ndata = 0;
 		return 0;
+	}
 	if (status == NVMX_VMENTRY_VMEXIT)
 		return 1;
 	WARN_ON_ONCE(status != NVMX_VMENTRY_VMFAIL);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index aa459fb327682..f0223a8beac31 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9779,6 +9779,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 		}
 		if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
 			if (unlikely(!kvm_nested_call(get_nested_state_pages)(vcpu))) {
+				vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+				vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+				vcpu->run->internal.ndata = 0;
 				kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);
 				r = 0;
 				goto out;
-- 
2.53.0