Re: [PATCH 1/3] intel-iommu: don't warn guest errors when getting rid2pasid entry

[Jason Wang <jasowang@redhat.com>]

在 2022/1/13 下午3:05, Michael S. Tsirkin 写道:
> On Thu, Jan 13, 2022 at 11:35:19AM +0800, Peter Xu wrote:
>> On Wed, Jan 05, 2022 at 12:19:43PM +0800, Jason Wang wrote:
>>> We use to warn on wrong rid2pasid entry. But this error could be
>>> triggered by the guest and could happens during initialization. So
>>> let's don't warn in this case.
>>>
>>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>>> ---
>>>   hw/i386/intel_iommu.c | 6 ++++--
>>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
>>> index 4c6c016388..f2c7a23712 100644
>>> --- a/hw/i386/intel_iommu.c
>>> +++ b/hw/i386/intel_iommu.c
>>> @@ -1524,8 +1524,10 @@ static bool vtd_dev_pt_enabled(IntelIOMMUState *s, VTDContextEntry *ce)
>>>       if (s->root_scalable) {
>>>           ret = vtd_ce_get_rid2pasid_entry(s, ce, &pe);
>>>           if (ret) {
>>> -            error_report_once("%s: vtd_ce_get_rid2pasid_entry error: %"PRId32,
>>> -                              __func__, ret);
>>> +            /*
>>> +             * This error is guest triggerable. We should assumt PT
>>> +             * not enabled for safety.
>>> +             */
>>>               return false;
>>>           }
>>>           return (VTD_PE_GET_TYPE(&pe) == VTD_SM_PASID_ENTRY_PT);
>>> -- 
>>> 2.25.1
>>>
>> No strong opinion, but the thing is mostly all error_report_once() in this file
>> is guest triggerable.  If we remove this one then it's debatable on whether we
>> want to remove all.
>>
>> IMHO we used the _once() variant just for this: it won't go into any form of
>> DoS, meanwhile we'll still get some information (as hypervisor) that the guest
>> OS may not be trustworthy.
>>
>> So from that pov it's still useful?  Or is this error very special in some way?
>>
>> Thanks,
>
> Well we have LOG_GUEST_ERROR for guest errors now.


Ok, but this is not necessarily a guest error. (Inferring from the 
comment in vtd_as_pt_enabled()).

Thanks


>
>> -- 
>> Peter Xu