linux-kernel - [PATCH v19 018/130] KVM: x86/mmu: Assume guest MMIOs are shared

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Message-Id: <b2e5c92fd66a0113b472dd602220346d3d435732.1708933498.git.isaku.yamahata@intel.com>
Date: Mon, 26 Feb 2024 00:25:20 -0800
From: isaku.yamahata@...el.com
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: isaku.yamahata@...el.com,
	isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>,
	erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>,
	Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com,
	hang.yuan@...el.com,
	tina.zhang@...el.com,
	Chao Gao <chao.gao@...el.com>
Subject: [PATCH v19 018/130] KVM: x86/mmu: Assume guest MMIOs are shared

From: Chao Gao <chao.gao@...el.com>

TODO: Drop this patch once the common patch is merged.

When memory slot isn't found for kvm page fault, handle it as MMIO.

The guest of TDX_VM, SNP_VM, or SW_PROTECTED_VM don't necessarily convert
the virtual MMIO range to shared before accessing it.  When the guest tries
to access the virtual device's MMIO without any private/shared conversion,
An NPT fault or EPT violation is raised first to find private-shared
mismatch.  Don't raise KVM_EXIT_MEMORY_FAULT, fall back to KVM_PFN_NOLSLOT.

Signed-off-by: Chao Gao <chao.gao@...el.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
v19:
- Added slot check before kvm_faultin_private_pfn()
- updated comment
- rewrite the commit message
---
 arch/x86/kvm/mmu/mmu.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index ca0c91f14063..c45252ed2ffd 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4342,6 +4342,7 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
 static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 {
 	struct kvm_memory_slot *slot = fault->slot;
+	bool force_mmio;
 	bool async;
 
 	/*
@@ -4371,12 +4372,21 @@ 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)) {
+	/*
+	 * !fault->slot means MMIO for SNP and TDX.  Don't require explicit GPA
+	 * conversion for MMIO because MMIO is assigned at the boot time.  Fall
+	 * to !is_private case to get pfn = KVM_PFN_NOSLOT.
+	 */
+	force_mmio = !slot &&
+		vcpu->kvm->arch.vm_type != KVM_X86_DEFAULT_VM &&
+		vcpu->kvm->arch.vm_type != KVM_X86_SW_PROTECTED_VM;
+	if (!force_mmio &&
+	    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)
+	if (!force_mmio && fault->is_private)
 		return kvm_faultin_pfn_private(vcpu, fault);
 
 	async = false;
-- 
2.25.1