lkml.org 
[lkml]   [2020]   [Nov]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: Question about domain_init (v5.3-v5.7)
Date

Lu Baolu @ 2020-11-26 19:12 MST:

> Hi Jerry,
>
> On 11/27/20 5:35 AM, Jerry Snitselaar wrote:
>> 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.
>
> MGAW indicates the max gpa width supported by 2nd translation. The VT-d
> spec requires that this value must be at least equal to the host
> physical addressibility. According to this, BIOS is good, right?
>

Yes, the host address width is 46. MGAW reports 57 (56+1), and highest
sagaw bit is for 48.


> For this failure case, domain_init() just wants to find a suitable agaw
> for the private domain. I think it makes sense to check against
> iommu->agaw instead of cap_mgaw.
>
> Best regards,
> baolu
>
>>
>>>
>>>> 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
>>>>
>>

\
 
 \ /
  Last update: 2020-11-27 08:49    [W:0.052 / U:0.612 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site