Re: Question about domain_init (v5.3-v5.7)

[Jerry Snitselaar <jsnitsel@redhat.com>]

Lu Baolu @ 2020-11-26 04:01 MST:

> Hi Jerry,
>
> On 2020/11/26 4:27, Jerry Snitselaar wrote:
>> Is there a reason we check the requested guest address width against
>> the
>> iommu's mgaw, instead of the agaw that we already know for the iommu?
>> I've run into a case with a new system where the mgaw reported is 57,
>> but if they set PAE to 46 instead of 52 in the bios, then sagaw reports
>> the highest supported agaw is 48 and the domain_init code fails here. In
>
> Isn't this a platform bug? If it's too late to fix it in the BIOS, you
> maybe have to add a platform specific quirk to set mgaw to the highest
> supported agaw?
>
> Best regards,
> baolu

Is there somewhere you can point me to that discusses how they should be
setting the mgaw? I misunderstood when I previously asked you about
whether the mgaw could be a value that was greater than any of sagaw.
If it is a bios issue, then they should fix it there.

>
>> other places like prepare_domain_attach_device, the dmar domain agaw
>> gets adjusted down to the iommu agaw. The agaw of the iommu gets
>> determined based off what is reported for sagaw. I'm wondering if it
>> can't instead do:
>> ---
>>   drivers/iommu/intel-iommu.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>> diff --git a/drivers/iommu/intel-iommu.c
>> b/drivers/iommu/intel-iommu.c
>> index 6ca5c92ef2e5..a8e41ec36d9e 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -1862,8 +1862,8 @@ static int domain_init(struct dmar_domain *domain, struct intel_iommu *iommu,
>>   	domain_reserve_special_ranges(domain);
>>   	/* calculate AGAW */
>> -	if (guest_width > cap_mgaw(iommu->cap))
>> -	        guest_width = cap_mgaw(iommu->cap);
>> +	if (guest_width > agaw_to_width(iommu->agaw))
>> +	        guest_width = agaw_to_width(iommu->agaw);
>>   	domain->gaw = guest_width;
>>   	adjust_width = guestwidth_to_adjustwidth(guest_width);
>>   	agaw = width_to_agaw(adjust_width);
>> --
>> 2.27.0
>> 
>> Thoughts? With the former code the ehci device for the ilo fails when
>> trying to get a private domain.
>> Thanks,
>> Jerry
>>