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From:   isaku.yamahata@intel.com
To:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     isaku.yamahata@intel.com, isaku.yamahata@gmail.com,
        Paolo Bonzini <pbonzini@redhat.com>, erdemaktas@google.com,
        Sean Christopherson <seanjc@google.com>,
        Sagi Shahar <sagis@google.com>
Subject: [PATCH v8 034/103] KVM: x86/mmu: Disallow fast page fault on private GPA
Date:   Sun,  7 Aug 2022 15:01:19 -0700
Message-Id: <0182c7c97d56d2a1b8a8589cec38bf1691f17fe5.1659854790.git.isaku.yamahata@intel.com>
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From: Isaku Yamahata <isaku.yamahata@intel.com>

TDX requires TDX SEAMCALL to operate Secure EPT instead of direct memory
access and TDX SEAMCALL is heavy operation.  Fast page fault on private GPA
doesn't make sense.  Disallow fast page fault on private GPA.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/mmu/mmu.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 88fc2218fcc3..1f7f61e04b94 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3231,8 +3231,16 @@ static int handle_abnormal_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fau
 	return RET_PF_CONTINUE;
 }
 
-static bool page_fault_can_be_fast(struct kvm_page_fault *fault)
+static bool page_fault_can_be_fast(struct kvm *kvm, struct kvm_page_fault *fault)
 {
+	/*
+	 * TDX private mapping doesn't support fast page fault because the EPT
+	 * entry is read/written with TDX SEAMCALLs instead of direct memory
+	 * access.
+	 */
+	if (kvm_is_private_gpa(kvm, fault->addr))
+		return false;
+
 	/*
 	 * Page faults with reserved bits set, i.e. faults on MMIO SPTEs, only
 	 * reach the common page fault handler if the SPTE has an invalid MMIO
@@ -3342,7 +3350,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 	u64 *sptep = NULL;
 	uint retry_count = 0;
 
-	if (!page_fault_can_be_fast(fault))
+	if (!page_fault_can_be_fast(vcpu->kvm, fault))
 		return ret;
 
 	walk_shadow_page_lockless_begin(vcpu);
-- 
2.25.1