linux-kernel - [PATCH v4 2/4] KVM: x86/mmu: Move private vs. shared check above slot validity checks

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Date: Fri,  9 Feb 2024 14:28:56 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Yan Zhao <yan.y.zhao@...el.com>, Friedrich Weber <f.weber@...xmox.com>, 
	Kai Huang <kai.huang@...el.com>, Yuan Yao <yuan.yao@...ux.intel.com>, 
	Xu Yilun <yilun.xu@...ux.intel.com>, Yu Zhang <yu.c.zhang@...ux.intel.com>, 
	Chao Peng <chao.p.peng@...ux.intel.com>, Fuad Tabba <tabba@...gle.com>, 
	Michael Roth <michael.roth@....com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	David Matlack <dmatlack@...gle.com>
Subject: [PATCH v4 2/4] KVM: x86/mmu: Move private vs. shared check above slot
 validity checks

Prioritize private vs. shared gfn attribute checks above slot validity
checks to ensure a consistent userspace ABI.  E.g. as is, KVM will exit to
userspace if there is no memslot, but emulate accesses to the APIC access
page even if the attributes mismatch.

Fixes: 8dd2eee9d526 ("KVM: x86/mmu: Handle page fault for private memory")
Cc: Yu Zhang <yu.c.zhang@...ux.intel.com>
Cc: Chao Peng <chao.p.peng@...ux.intel.com>
Cc: Fuad Tabba <tabba@...gle.com>
Cc: Michael Roth <michael.roth@....com>
Cc: Isaku Yamahata <isaku.yamahata@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/mmu/mmu.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 166cef0c3ff4..50bfaa53f3f2 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4360,11 +4360,6 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
 			return RET_PF_EMULATE;
 	}
 
-	if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
-		kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
-		return -EFAULT;
-	}
-
 	if (fault->is_private)
 		return kvm_faultin_pfn_private(vcpu, fault);
 
@@ -4403,6 +4398,11 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
 	struct kvm_memory_slot *slot = fault->slot;
 	int ret;
 
+	if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
+		kvm_mmu_prepare_memory_fault_exit(vcpu, fault);
+		return -EFAULT;
+	}
+
 	fault->mmu_seq = vcpu->kvm->mmu_invalidate_seq;
 	smp_rmb();
 
-- 
2.43.0.687.g38aa6559b0-goog