[PATCH v6 41/44] KVM: VMX: Compartmentalize adding MSRs to host vs. guest auto-load list

[Mi, Dapeng]

On 12/6/2025 8:17 AM, Sean Christopherson wrote:
> Undo the bundling of the "host" and "guest" MSR auto-load list logic so
> that the code can be deduplicated by factoring out the logic to a separate
> helper.  Now that "list full" situations are treated as fatal to the VM,
> there is no need to pre-check both lists.
>
> For all intents and purposes, this reverts the add_atomic_switch_msr()
> changes made by commit 3190709335dd ("x86/KVM/VMX: Separate the VMX
> AUTOLOAD guest/host number accounting").
>
> Signed-off-by: Sean Christopherson <seanjc at google.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index be2a2580e8f1..018e01daab68 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1096,9 +1096,9 @@ static __always_inline void add_atomic_switch_msr_special(struct vcpu_vmx *vmx,
>  static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
>  				  u64 guest_val, u64 host_val)
>  {
> -	int i, j = 0;
>  	struct msr_autoload *m = &vmx->msr_autoload;
>  	struct kvm *kvm = vmx->vcpu.kvm;
> +	int i;
>  
>  	switch (msr) {
>  	case MSR_EFER:
> @@ -1133,25 +1133,26 @@ static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
>  	}
>  
>  	i = vmx_find_loadstore_msr_slot(&m->guest, msr);
> -	j = vmx_find_loadstore_msr_slot(&m->host, msr);
> -
> -	if (KVM_BUG_ON(i < 0 && m->guest.nr == MAX_NR_LOADSTORE_MSRS, kvm) ||
> -	    KVM_BUG_ON(j < 0 &&  m->host.nr == MAX_NR_LOADSTORE_MSRS, kvm))
> -		return;
> -
>  	if (i < 0) {
> +		if (KVM_BUG_ON(m->guest.nr == MAX_NR_LOADSTORE_MSRS, kvm))
> +			return;
> +
>  		i = m->guest.nr++;
>  		m->guest.val[i].index = msr;
>  		vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, m->guest.nr);
>  	}
>  	m->guest.val[i].value = guest_val;
>  
> -	if (j < 0) {
> -		j = m->host.nr++;
> -		m->host.val[j].index = msr;
> +	i = vmx_find_loadstore_msr_slot(&m->host, msr);
> +	if (i < 0) {
> +		if (KVM_BUG_ON(m->host.nr == MAX_NR_LOADSTORE_MSRS, kvm))
> +			return;
> +
> +		i = m->host.nr++;
> +		m->host.val[i].index = msr;
>  		vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, m->host.nr);
>  	}
> -	m->host.val[j].value = host_val;
> +	m->host.val[i].value = host_val;
>  }
>  
>  static bool update_transition_efer(struct vcpu_vmx *vmx)

Reviewed-by: Dapeng Mi <dapeng1.mi at linux.intel.com>