Re: [PATCH v4 1/8] KVM: nVMX: Keep KVM updates to BNDCFGS ctrl bits across MSR write

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 3/1/22 07:03, Oliver Upton wrote:
> +
> +	/*
> +	 * Ensure KVM fiddling with these MSRs is preserved after userspace
> +	 * write.
> +	 */
> +	if (msr_index == MSR_IA32_VMX_TRUE_ENTRY_CTLS ||
> +	    msr_index == MSR_IA32_VMX_TRUE_EXIT_CTLS)
> +		nested_vmx_entry_exit_ctls_update(&vmx->vcpu);
> +

I still don't understand this patch.  You say:

> Now, the BNDCFGS bits are only ever
> updated after a KVM_SET_CPUID/KVM_SET_CPUID2 ioctl, meaning that a
> subsequent MSR write from userspace will clobber these values.

but I don't understand what's wrong with that.  If you can (if so 
inclined) define a VM without LOAD_BNDCFGS or CLEAR_BNDCFGS even if MPX 
enabled, commit aedbaf4f6afd counts as a bugfix.

Paolo