Re: [PATCH v2 17/25] KVM: nVMX: Add support for the secondary VM exit controls

On Wed, Feb 07, 2024, Xin Li wrote:

@@ -6856,13 +6865,17 @@ static void nested_vmx_setup_exit_ctls(struct vmcs_config *vmcs_conf, VM_EXIT_HOST_ADDR_SPACE_SIZE | #endif VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT |

• VM_EXIT_CLEAR_BNDCFGS;
  

• VM_EXIT_CLEAR_BNDCFGS | VM_EXIT_ACTIVATE_SECONDARY_CONTROLS;
  

  msrs->exit_ctls_high |= VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR | VM_EXIT_LOAD_IA32_EFER | VM_EXIT_SAVE_IA32_EFER | VM_EXIT_SAVE_VMX_PREEMPTION_TIMER | VM_EXIT_ACK_INTR_ON_EXIT | VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL;

• /* secondary exit controls */

Drop the comment, it's pretty obvious what field is being setup.

• if (msrs->exit_ctls_high & VM_EXIT_ACTIVATE_SECONDARY_CONTROLS)

• rdmsrl(MSR_IA32_VMX_EXIT_CTLS2, msrs->secondary_exit_ctls);
  

This is wrong, the resulting msrs->secondary_exit_ctls needs to be sanitized based on what KVM supports for nVMX.

On a very related topic, this should not do a raw RDMSR. One of the reasons why KVM uses vmcs_config as the base is to avoid advertising features to L1 that KVM itself doesn't support, e.g. because the expected entry+exit pairs aren't supported.

And by pulling state from vmcs_conf->secondary_exit_ctls there's no need to check the activation bit.

I.e. literaly just this:

msrs->secondary_exit_ctls = vmcs_conf->secondary_exit_ctls; msrs->secondary_exit_ctls &= 0;

and then when nVMX FRED support is ready, it becomes:

msrs->secondary_exit_ctls = vmcs_conf->secondary_exit_ctls; msrs->secondary_exit_ctls &= SECONDARY_VM_EXIT_SAVE_IA32_FRED | SECONDARY_VM_EXIT_LOAD_IA32_FRED;