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| author | Sean Christopherson <seanjc@google.com> | 2023-04-13 16:19:13 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2023-05-26 13:50:42 -0700 |
| commit | 3243b93c16d90c2d63cf30655276ffdf5bb65bf7 (patch) | |
| tree | 2685594bb0476dde3b197fea8cc983e51afbab58 /arch/x86/kvm/vmx/nested.c | |
| parent | 82dc11b82b001ca8024663b3e7990b59f600841f (diff) | |
| download | linux-stable-3243b93c16d90c2d63cf30655276ffdf5bb65bf7.tar.gz linux-stable-3243b93c16d90c2d63cf30655276ffdf5bb65bf7.tar.bz2 linux-stable-3243b93c16d90c2d63cf30655276ffdf5bb65bf7.zip | |
KVM: VMX: Treat UMIP as emulated if and only if the host doesn't have UMIP
Advertise UMIP as emulated if and only if the host doesn't natively
support UMIP, otherwise vmx_umip_emulated() is misleading when the host
_does_ support UMIP. Of the four users of vmx_umip_emulated(), two
already check for native support, and the logic in vmx_set_cpu_caps() is
relevant if and only if UMIP isn't natively supported as UMIP is set in
KVM's caps by kvm_set_cpu_caps() when UMIP is present in hardware.
That leaves KVM's stuffing of X86_CR4_UMIP into the default cr4_fixed1
value enumerated for nested VMX. In that case, checking for (lack of)
host support is actually a bug fix of sorts, as enumerating UMIP support
based solely on descriptor table exiting works only because KVM doesn't
sanity check MSR_IA32_VMX_CR4_FIXED1. E.g. if a (very theoretical) host
supported UMIP in hardware but didn't allow UMIP+VMX, KVM would advertise
UMIP but not actually emulate UMIP. Of course, KVM would explode long
before it could run a nested VM on said theoretical CPU, as KVM doesn't
modify host CR4 when enabling VMX, i.e. would load an "illegal" value into
vmcs.HOST_CR4.
Reported-by: Robert Hoo <robert.hu@intel.com>
Link: https://lore.kernel.org/all/20230310125718.1442088-2-robert.hu@intel.com
Link: https://lore.kernel.org/r/20230413231914.1482782-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'arch/x86/kvm/vmx/nested.c')
| -rw-r--r-- | arch/x86/kvm/vmx/nested.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index e35cf0bd0df9..368a43e3b40e 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -2328,8 +2328,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0 * Preset *DT exiting when emulating UMIP, so that vmx_set_cr4() * will not have to rewrite the controls just for this bit. */ - if (!boot_cpu_has(X86_FEATURE_UMIP) && vmx_umip_emulated() && - (vmcs12->guest_cr4 & X86_CR4_UMIP)) + if (vmx_umip_emulated() && (vmcs12->guest_cr4 & X86_CR4_UMIP)) exec_control |= SECONDARY_EXEC_DESC; if (exec_control & SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY) |