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

Bandan Das
2016-07-21T19:18:13Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> 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 regarding nested vpid support since it is no longer valid.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;
> }

Ah ok, this should be sufficient I think.

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

Yeah, a trace isn't really necessary. We know where it's from.
BUG() can also leave the module in an unclean state and prevent
it from getting unloaded which I why I think it shouldn't be on
any path that can be guest triggered.

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

I will drop it and modify the commit message accordingly.

> Paolo