Re: [PATCH v2 2/5] x86: KVM: svm: avoid flooding logs when skip_emulated_instruction() fails

Vitaly Kuznetsov
2019-08-07T11:17:13Z

Sean Christopherson <sean.j.christopherson@intel.com> writes:

> On Tue, Aug 06, 2019 at 08:01:47AM +0200, Vitaly Kuznetsov wrote:
>> When we're unable to skip instruction with kvm_emulate_instruction() we
>> will not advance RIP and most likely the guest will get stuck as
>> consequitive attempts to execute the same instruction will likely result
>> in the same behavior.
>>
>> As we're not supposed to see these messages under normal conditions, switch
>> to pr_err_once().
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> Reviewed-by: Jim Mattson <jmattson@google.com>
>> ---
>> arch/x86/kvm/svm.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 7e843b340490..80f576e05112 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -782,7 +782,8 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
>> if (!svm->next_rip) {
>> if (kvm_emulate_instruction(vcpu, EMULTYPE_SKIP) !=
>> EMULATE_DONE)
>> - printk(KERN_DEBUG "%s: NOP\n", __func__);
>> + pr_err_once("KVM: %s: unable to skip instruction\n",
>> + __func__);
>
> IMO the proper fix would be to change skip_emulated_instruction() to
> return an int so that emulation failure can be reported back up the stack.
> It's a relatively minor change as there are a limited number of call sites
> to skip_emulated_instruction() in SVM and VMX.
>

(I'm always wondering when is the right time to add "plus a bunch of
miscellaneous fixes all over" to the PATCH0's Subject line :-)

Will do in the next version, thanks!

>> return;
>> }
>> if (svm->next_rip - kvm_rip_read(vcpu) > MAX_INST_SIZE)
>> --
>> 2.20.1
>>

--
Vitaly