Re: [PATCH v2 04/10] iommu/vt-d: Match CPU and IOMMU paging mode

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

On Tue, 19 Nov 2019 09:04:10 +0100
Auger Eric <eric.auger@redhat.com> wrote:

> Hi Lu, Jacob,
> 
> On 11/19/19 4:06 AM, Lu Baolu wrote:
> > Hi Eric and Jacob,
> > 
> > On 11/19/19 5:52 AM, Jacob Pan wrote:  
> >> On Mon, 18 Nov 2019 21:55:03 +0100
> >> Auger Eric <eric.auger@redhat.com> wrote:
> >>  
> >>> Hi Jacob,
> >>>
> >>> On 11/18/19 8:42 PM, Jacob Pan wrote:  
> >>>> When setting up first level page tables for sharing with CPU, we
> >>>> need to ensure IOMMU can support no less than the levels
> >>>> supported by the CPU.
> >>>> It is not adequate, as in the current code, to set up 5-level
> >>>> paging in PASID entry First Level Paging Mode(FLPM) solely based
> >>>> on CPU.
> >>>>
> >>>> Fixes: 437f35e1cd4c8 ("iommu/vt-d: Add first level page table
> >>>> interface")
> >>>> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> >>>> Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
> >>>> ---
> >>>>   drivers/iommu/intel-pasid.c | 12 ++++++++++--
> >>>>   1 file changed, 10 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/drivers/iommu/intel-pasid.c
> >>>> b/drivers/iommu/intel-pasid.c index 040a445be300..e7cb0b8a7332
> >>>> 100644 --- a/drivers/iommu/intel-pasid.c
> >>>> +++ b/drivers/iommu/intel-pasid.c
> >>>> @@ -499,8 +499,16 @@ int intel_pasid_setup_first_level(struct
> >>>> intel_iommu *iommu, }
> >>>>     #ifdef CONFIG_X86
> >>>> -    if (cpu_feature_enabled(X86_FEATURE_LA57))
> >>>> -        pasid_set_flpm(pte, 1);
> >>>> +    /* Both CPU and IOMMU paging mode need to match */
> >>>> +    if (cpu_feature_enabled(X86_FEATURE_LA57)) {
> >>>> +        if (cap_5lp_support(iommu->cap)) {
> >>>> +            pasid_set_flpm(pte, 1);
> >>>> +        } else {
> >>>> +            pr_err("VT-d has no 5-level paging support
> >>>> for CPU\n");
> >>>> +            pasid_clear_entry(pte);
> >>>> +            return -EINVAL;  
> >>> Can it happen? If I am not wrong intel_pasid_setup_first_level()
> >>> only seems to be called from intel_svm_bind_mm which now checks
> >>> the SVM_CAPABLE flag.
> >>>  
> >> You are right, this check is not needed any more. I will drop the
> >> patch.  
> >>> Thanks  
> > 
> > I'd suggest to keep this. This helper is not only for svm, although
> > currently svm is the only caller. For first level pasid setup, let's
> > set an assumption that hardware should never report mismatching
> > paging modes, this is helpful especially when running vIOMMU in VM
> > guests.  
> 
> OK. So maybe just add the rationale in the commit message?
> 
OK. will do. I thought about Baolu's point as well then I thought the
other use of first level map for replacing today's VFIO second level
map in the guest, but that will have a different helper. Anyway, I will
keep this one then.

Thanks you both!

> Thanks
> 
> Eric
> > 
> > Best regards,
> > baolu
> >   
> 

[Jacob Pan]