Re: [PATCH 1/4] nvmx: use warn_on for buggy cases when emulating invept/invvpid

Paolo Bonzini
2016-07-21T09:13:37Z

On 21/07/2016 00:25, Bandan Das wrote:
> If L1 hypervisor decides to try out something weird, alert the
> host but only less aggressively. Also, remove the comment
> regarding nested vpid support since it is no longer valid.
>
> Signed-off-by: Bandan Das <bsd@redhat.com>
> ---
> arch/x86/kvm/vmx.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 64a79f2..9fd0681 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2854,7 +2854,6 @@ static int vmx_get_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
> vmx->nested.nested_vmx_secondary_ctls_high);
> break;
> case MSR_IA32_VMX_EPT_VPID_CAP:
> - /* Currently, no nested vpid support */

This is okay.

> *pdata = vmx->nested.nested_vmx_ept_caps |
> ((u64)vmx->nested.nested_vmx_vpid_caps << 32);
> break;
> @@ -7462,7 +7461,7 @@ static int handle_invept(struct kvm_vcpu *vcpu)
> break;
> default:
> /* Trap single context invalidation invept calls */
> - BUG_ON(1);
> + WARN_ON(1);
> break;
> }
>
> @@ -7525,7 +7524,7 @@ static int handle_invvpid(struct kvm_vcpu *vcpu)
> break;
> default:
> /* Trap individual address invalidation invvpid calls */
> - BUG_ON(1);
> + WARN_ON(1);
> break;
> }
>
>

These are BUGs because they are checked above:

if (!(types & (1UL << type))) {
nested_vmx_failValid(vcpu,
VMXERR_INVALID_OPERAND_TO_INVEPT_INVVPID);
skip_emulated_instruction(vcpu);
return 1;
}

Guest-triggerable WARNs are only just a little better than
guest-triggerable BUGs. Guest-triggerable messages should be
rate-limited printk.

I don't object to the change, but the commit message should be
modified (or the change dropped).

Paolo