Commit c75d0edc authored Mar 29, 2018 by Sean Christopherson Committed by Paolo Bonzini Apr 04, 2018

KVM: VMX: remove bogus WARN_ON in handle_ept_misconfig



Remove the WARN_ON in handle_ept_misconfig() as it is unnecessary
and causes false positives.  Return the unmodified result of
kvm_mmu_page_fault() instead of converting a system error code to
KVM_EXIT_UNKNOWN so that userspace sees the error code of the
actual failure, not a generic "we don't know what went wrong".

  * kvm_mmu_page_fault() will WARN if reserved bits are set in the
    SPTEs, i.e. it covers the case where an EPT misconfig occurred
    because of a KVM bug.

  * The WARN_ON will fire on any system error code that is hit while
    handling the fault, e.g. -ENOMEM from mmu_topup_memory_caches()
    while handling a legitmate MMIO EPT misconfig or -EFAULT from
    kvm_handle_bad_page() if the corresponding HVA is invalid.  In
    either case, userspace should receive the original error code
    and firing a warning is incorrect behavior as KVM is operating
    as designed.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 2c151b25

arch/x86/kvm/vmx.c

+1 −12

Original line number	Diff line number	Diff line
		@@ -7078,7 +7078,6 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)

		static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
		{
		int ret;
		gpa_t gpa;

		/*
		@@ -7106,17 +7105,7 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
		NULL, 0) == EMULATE_DONE;
		}

		ret = kvm_mmu_page_fault(vcpu, gpa, PFERR_RSVD_MASK, NULL, 0);
		if (ret >= 0)
		return ret;

		/* It is the real ept misconfig */
		WARN_ON(1);

		vcpu->run->exit_reason = KVM_EXIT_UNKNOWN;
		vcpu->run->hw.hardware_exit_reason = EXIT_REASON_EPT_MISCONFIG;

		return 0;
		return kvm_mmu_page_fault(vcpu, gpa, PFERR_RSVD_MASK, NULL, 0);
		}

		static int handle_nmi_window(struct kvm_vcpu *vcpu)

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