[PATCH 3/4] KVM: x86: WARN and reject loading KVM if NX is supported but not enabled

From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 3/4] KVM: x86: WARN and reject loading KVM if NX is supported but not enabled
Date: Tue, 15 Jun 2021 09:45:34 -0700	[thread overview]
Message-ID: <20210615164535.2146172-4-seanjc@google.com> (raw)
In-Reply-To: <20210615164535.2146172-1-seanjc@google.com>

WARN if NX is reported as supported but not enabled in EFER.  All flavors
of the kernel, including non-PAE 32-bit kernels, set EFER.NX=1 if NX is
supported, even if NX usage is disable via kernel command line.  KVM relies
on NX being enabled if it's supported, e.g. KVM will generate illegal NPT
entries if nx_huge_pages is enabled and NX is supported but not enabled.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index acc28473dec7..1f6595df45de 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10981,6 +10981,9 @@ int kvm_arch_hardware_setup(void *opaque)
 	int r;
 
 	rdmsrl_safe(MSR_EFER, &host_efer);
+	if (WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_NX) &&
+			 !(host_efer & EFER_NX)))
+		return -EIO;
 
 	if (boot_cpu_has(X86_FEATURE_XSAVES))
 		rdmsrl(MSR_IA32_XSS, host_xss);
-- 
2.32.0.272.g935e593368-goog

