Re: [PATCH v19 110/130] KVM: TDX: Handle TDX PV MMIO hypercall

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On 2/26/2024 4:26 PM, isaku.yamahata@xxxxxxxxx wrote:
From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

Export kvm_io_bus_read and kvm_mmio tracepoint and wire up TDX PV MMIO
hypercall to the KVM backend functions.

kvm_io_bus_read/write() searches KVM device emulated in kernel of the given
MMIO address and emulates the MMIO.  As TDX PV MMIO also needs it, export
kvm_io_bus_read().  kvm_io_bus_write() is already exported.  TDX PV MMIO
emulates some of MMIO itself.  To add trace point consistently with x86
kvm, export kvm_mmio tracepoint.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
  arch/x86/kvm/vmx/tdx.c | 114 +++++++++++++++++++++++++++++++++++++++++
  arch/x86/kvm/x86.c     |   1 +
  virt/kvm/kvm_main.c    |   2 +
  3 files changed, 117 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 55fc6cc6c816..389bb95d2af0 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1217,6 +1217,118 @@ static int tdx_emulate_io(struct kvm_vcpu *vcpu)
  	return ret;
  }
+static int tdx_complete_mmio(struct kvm_vcpu *vcpu)
+{
+	unsigned long val = 0;
+	gpa_t gpa;
+	int size;
+
+	KVM_BUG_ON(vcpu->mmio_needed != 1, vcpu->kvm);
+	vcpu->mmio_needed = 0;
+
+	if (!vcpu->mmio_is_write) {
+		gpa = vcpu->mmio_fragments[0].gpa;
+		size = vcpu->mmio_fragments[0].len;
+
+		memcpy(&val, vcpu->run->mmio.data, size);
+		tdvmcall_set_return_val(vcpu, val);
+		trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
+	}
+	return 1;
+}
+
+static inline int tdx_mmio_write(struct kvm_vcpu *vcpu, gpa_t gpa, int size,
+				 unsigned long val)
+{
+	if (kvm_iodevice_write(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
+	    kvm_io_bus_write(vcpu, KVM_MMIO_BUS, gpa, size, &val))
+		return -EOPNOTSUPP;
+
+	trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, size, gpa, &val);
+	return 0;
+}
+
+static inline int tdx_mmio_read(struct kvm_vcpu *vcpu, gpa_t gpa, int size)
+{
+	unsigned long val;
+
+	if (kvm_iodevice_read(vcpu, &vcpu->arch.apic->dev, gpa, size, &val) &&
+	    kvm_io_bus_read(vcpu, KVM_MMIO_BUS, gpa, size, &val))
+		return -EOPNOTSUPP;
+
+	tdvmcall_set_return_val(vcpu, val);
+	trace_kvm_mmio(KVM_TRACE_MMIO_READ, size, gpa, &val);
+	return 0;
+}
+
+static int tdx_emulate_mmio(struct kvm_vcpu *vcpu)
+{
+	struct kvm_memory_slot *slot;
+	int size, write, r;
+	unsigned long val;
+	gpa_t gpa;
+
+	KVM_BUG_ON(vcpu->mmio_needed, vcpu->kvm);
+
+	size = tdvmcall_a0_read(vcpu);
+	write = tdvmcall_a1_read(vcpu);
+	gpa = tdvmcall_a2_read(vcpu);
+	val = write ? tdvmcall_a3_read(vcpu) : 0;
+
+	if (size != 1 && size != 2 && size != 4 && size != 8)
+		goto error;
+	if (write != 0 && write != 1)
+		goto error;
+
+	/* Strip the shared bit, allow MMIO with and without it set. */
Based on the discussion https://lore.kernel.org/all/ZcUO5sFEAIH68JIA@xxxxxxxxxx/
Do we still allow the MMIO without shared bit?

+	gpa = gpa & ~gfn_to_gpa(kvm_gfn_shared_mask(vcpu->kvm));
+
+	if (size > 8u || ((gpa + size - 1) ^ gpa) & PAGE_MASK)
"size > 8u" can be removed, since based on the check of size above, it can't be greater than 8.


+		goto error;
+
+	slot = kvm_vcpu_gfn_to_memslot(vcpu, gpa_to_gfn(gpa));
+	if (slot && !(slot->flags & KVM_MEMSLOT_INVALID))
+		goto error;
+
+	if (!kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
Should this be checked for write first?

I check the handle_ept_misconfig() in VMX, it doesn't check write first neither.

Functionally, it should be OK since guest will not read the address range of fast mmio.
So the read case will be filtered out by ioeventfd_write().
But it has take a long way to get to ioeventfd_write().
Isn't it more efficient to check write first?


+		trace_kvm_fast_mmio(gpa);
+		return 1;
+	}
+
+	if (write)
+		r = tdx_mmio_write(vcpu, gpa, size, val);
+	else
+		r = tdx_mmio_read(vcpu, gpa, size);
+	if (!r) {
+		/* Kernel completed device emulation. */
+		tdvmcall_set_return_code(vcpu, TDVMCALL_SUCCESS);
+		return 1;
+	}
+
+	/* Request the device emulation to userspace device model. */
+	vcpu->mmio_needed = 1;
+	vcpu->mmio_is_write = write;
+	vcpu->arch.complete_userspace_io = tdx_complete_mmio;
+
+	vcpu->run->mmio.phys_addr = gpa;
+	vcpu->run->mmio.len = size;
+	vcpu->run->mmio.is_write = write;
+	vcpu->run->exit_reason = KVM_EXIT_MMIO;
+
+	if (write) {
+		memcpy(vcpu->run->mmio.data, &val, size);
+	} else {
+		vcpu->mmio_fragments[0].gpa = gpa;
+		vcpu->mmio_fragments[0].len = size;
+		trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, size, gpa, NULL);
+	}
+	return 0;
+
+error:
+	tdvmcall_set_return_code(vcpu, TDVMCALL_INVALID_OPERAND);
+	return 1;
+}
+
  static int handle_tdvmcall(struct kvm_vcpu *vcpu)
  {
  	if (tdvmcall_exit_type(vcpu))
@@ -1229,6 +1341,8 @@ static int handle_tdvmcall(struct kvm_vcpu *vcpu)
  		return tdx_emulate_hlt(vcpu);
  	case EXIT_REASON_IO_INSTRUCTION:
  		return tdx_emulate_io(vcpu);
+	case EXIT_REASON_EPT_VIOLATION:
+		return tdx_emulate_mmio(vcpu);
  	default:
  		break;
  	}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 03950368d8db..d5b18cad9dcd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -13975,6 +13975,7 @@ EXPORT_SYMBOL_GPL(kvm_sev_es_string_io);
EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_entry);
  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
+EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_mmio);
  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_inj_virq);
  EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_page_fault);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e27c22449d85..bc14e1f2610c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2689,6 +2689,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn
return NULL;
  }
+EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot);
bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
  {
@@ -5992,6 +5993,7 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
  	r = __kvm_io_bus_read(vcpu, bus, &range, val);
  	return r < 0 ? r : 0;
  }
+EXPORT_SYMBOL_GPL(kvm_io_bus_read);
int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
  			    int len, struct kvm_io_device *dev)





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