Messages in this thread | | | Date | Tue, 28 Jun 2022 01:38:17 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH 04/14] KVM: VMX: Extend VMX controls macro shenanigans |
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On Mon, Jun 27, 2022, Dong, Eddie wrote: > > static inline void lname##_controls_clearbit(struct vcpu_vmx *vmx, u##bits > > val) \ > > { > > \ > > + BUILD_BUG_ON(!(val & (KVM_REQ_VMX_##uname | > > KVM_OPT_VMX_##uname))); \ > > lname##_controls_set(vmx, lname##_controls_get(vmx) & ~val); > > \ > > } > > With this, will it be safer if we present L1 CTRL MSRs with the bits KVM > really uses? Do I miss something?
KVM will still allow L1 to use features/controls that KVM itself doesn't use, but exposing features/controls that KVM doesn't use will require a more explicit "override" of sorts, e.g. to prevent advertising features that are supported in hardware, known to KVM, but disabled for whatever reason, e.g. a CPU bug, eVMCS incompatibility, module param, etc...
The intent of this BUILD_BUG_ON() is to detect KVM usage of bits that aren't enabled by default, i.e. to lower the probability that a control gets used by KVM but isn't exposed to L1 because it's a dynamically enabled control.
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