[PATCH 5.18 0797/1095] KVM: nVMX: Set UMIP bit CR4_FIXED1 MSR when emulating UMIP

Greg Kroah-Hartman
2022-08-15T22:32:17Z

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit a910b5ab6b250a88fff1866bf708642d83317466 ]

Make UMIP an "allowed-1" bit CR4_FIXED1 MSR when KVM is emulating UMIP.
KVM emulates UMIP for both L1 and L2, and so should enumerate that L2 is
allowed to have CR4.UMIP=1. Not setting the bit doesn't immediately
break nVMX, as KVM does set/clear the bit in CR4_FIXED1 in response to a
guest CPUID update, i.e. KVM will correctly (dis)allow nested VM-Entry
based on whether or not UMIP is exposed to L1. That said, KVM should
enumerate the bit as being allowed from time zero, e.g. userspace will
see the wrong value if the MSR is read before CPUID is written.

Fixes: 0367f205a3b7 ("KVM: vmx: add support for emulating UMIP")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220607213604.3346000-12-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/vmx/nested.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index c632df13ada2..aa287302f991 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6790,6 +6790,9 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
rdmsrl(MSR_IA32_VMX_CR0_FIXED1, msrs->cr0_fixed1);
rdmsrl(MSR_IA32_VMX_CR4_FIXED1, msrs->cr4_fixed1);

+ if (vmx_umip_emulated())
+ msrs->cr4_fixed1 |= X86_CR4_UMIP;
+
msrs->vmcs_enum = nested_vmx_calc_vmcs_enum_msr();
}

--
2.35.1