[PATCH v19 101/130] KVM: TDX: handle ept violation/misconfig exit

isaku.yamahata
2024-02-26T08:28:58Z

From: Isaku Yamahata <isaku.yamahata@intel.com>

On EPT violation, call a common function, __vmx_handle_ept_violation() to
trigger x86 MMU code. On EPT misconfiguration, exit to ring 3 with
KVM_EXIT_UNKNOWN. because EPT misconfiguration can't happen as MMIO is
trigged by TDG.VP.VMCALL. No point to set a misconfiguration value for the
fast path.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>

---
v14 -> v15:
- use PFERR_GUEST_ENC_MASK to tell the fault is private

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
arch/x86/kvm/vmx/common.h | 3 +++
arch/x86/kvm/vmx/tdx.c | 49 +++++++++++++++++++++++++++++++++++++++
2 files changed, 52 insertions(+)

diff --git a/arch/x86/kvm/vmx/common.h b/arch/x86/kvm/vmx/common.h
index 632af7a76d0a..027aa4175d2c 100644
--- a/arch/x86/kvm/vmx/common.h
+++ b/arch/x86/kvm/vmx/common.h
@@ -87,6 +87,9 @@ static inline int __vmx_handle_ept_violation(struct kvm_vcpu *vcpu, gpa_t gpa,
error_code |= (exit_qualification & EPT_VIOLATION_GVA_TRANSLATED) != 0 ?
PFERR_GUEST_FINAL_MASK : PFERR_GUEST_PAGE_MASK;

+ if (kvm_is_private_gpa(vcpu->kvm, gpa))
+ error_code |= PFERR_GUEST_ENC_MASK;
+
return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
}

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 2f68e6f2b53a..0db80fa020d2 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1285,6 +1285,51 @@ void tdx_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
__vmx_deliver_posted_interrupt(vcpu, &tdx->pi_desc, vector);
}

+static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
+{
+ unsigned long exit_qual;
+
+ if (kvm_is_private_gpa(vcpu->kvm, tdexit_gpa(vcpu))) {
+ /*
+ * Always treat SEPT violations as write faults. Ignore the
+ * EXIT_QUALIFICATION reported by TDX-SEAM for SEPT violations.
+ * TD private pages are always RWX in the SEPT tables,
+ * i.e. they're always mapped writable. Just as importantly,
+ * treating SEPT violations as write faults is necessary to
+ * avoid COW allocations, which will cause TDAUGPAGE failures
+ * due to aliasing a single HPA to multiple GPAs.
+ */
+#define TDX_SEPT_VIOLATION_EXIT_QUAL EPT_VIOLATION_ACC_WRITE
+ exit_qual = TDX_SEPT_VIOLATION_EXIT_QUAL;
+ } else {
+ exit_qual = tdexit_exit_qual(vcpu);
+ if (exit_qual & EPT_VIOLATION_ACC_INSTR) {
+ pr_warn("kvm: TDX instr fetch to shared GPA = 0x%lx @ RIP = 0x%lx\n",
+ tdexit_gpa(vcpu), kvm_rip_read(vcpu));
+ vcpu->run->exit_reason = KVM_EXIT_EXCEPTION;
+ vcpu->run->ex.exception = PF_VECTOR;
+ vcpu->run->ex.error_code = exit_qual;
+ return 0;
+ }
+ }
+
+ trace_kvm_page_fault(vcpu, tdexit_gpa(vcpu), exit_qual);
+ return __vmx_handle_ept_violation(vcpu, tdexit_gpa(vcpu), exit_qual);
+}
+
+static int tdx_handle_ept_misconfig(struct kvm_vcpu *vcpu)
+{
+ WARN_ON_ONCE(1);
+
+ vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+ vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
+ vcpu->run->internal.ndata = 2;
+ vcpu->run->internal.data[0] = EXIT_REASON_EPT_MISCONFIG;
+ vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
+
+ return 0;
+}
+
int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
{
union tdx_exit_reason exit_reason = to_tdx(vcpu)->exit_reason;
@@ -1345,6 +1390,10 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
WARN_ON_ONCE(fastpath != EXIT_FASTPATH_NONE);

switch (exit_reason.basic) {
+ case EXIT_REASON_EPT_VIOLATION:
+ return tdx_handle_ept_violation(vcpu);
+ case EXIT_REASON_EPT_MISCONFIG:
+ return tdx_handle_ept_misconfig(vcpu);
case EXIT_REASON_OTHER_SMI:
/*
* If reach here, it's not a Machine Check System Management
--
2.25.1