Re: [RFC PATCH] KVM: PPC: Book3S HV: add support for page faults in VM_IO|VM_PFNMAP vmas

[Paolo Bonzini <pbonzini@redhat.com>]

On 09/02/2018 08:14, Cédric Le Goater wrote:
>>> @@ -402,8 +450,15 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
>>>                 vma = find_vma(current->mm, hva);
>>>                 if (vma && vma->vm_start <= hva && hva < vma->vm_end &&
>>>                     (vma->vm_flags & VM_PFNMAP)) {
>>> -                       pfn = vma->vm_pgoff +
>>> -                               ((hva - vma->vm_start) >> PAGE_SHIFT);
>>> +                       if (vma->vm_flags & (VM_IO | VM_PFNMAP)) {
>>> +                               ret = hva_to_pfn_remapped(vma, hva, writing,
>>> +                                                         &pfn);
>>> +                               if (ret == -EAGAIN)
>>> +                                       return RESUME_GUEST;
>>> +                       } else {
>>> +                               pfn = vma->vm_pgoff +
>>> +                                       ((hva - vma->vm_start) >> PAGE_SHIFT);
>>> +                       }
>> I don't think the else case is useful. If fact you are checking
>> VM_PFNMAP twice...
> yes. I am not sure what the VM_PFNMAP case does. The code comes 
> from kvmppc_book3s_hv_page_fault() I suppose.

Maybe the outer check should be for VM_IO|VM_PFNMAP?

(Also, why is this code reinventing most of hva_to_pfn?  Not asking you
to fix that of course, but perhaps there's something to improve in the
generic code too).

Thanks,

Paolo