Re: [v4 4/5] KVM: PPC: Book3S HV: retry page migration before erroring-out

[Bharata B Rao <bharata@linux.ibm.com>]

On Fri, Jul 17, 2020 at 01:00:26AM -0700, Ram Pai wrote:
> @@ -812,7 +842,7 @@ unsigned long kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
>  	struct vm_area_struct *vma;
>  	int srcu_idx;
>  	unsigned long gfn = gpa >> page_shift;
> -	int ret;
> +	int ret, repeat_count = REPEAT_COUNT;
>  
>  	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
>  		return H_UNSUPPORTED;
> @@ -826,34 +856,44 @@ unsigned long kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
>  	if (flags & H_PAGE_IN_SHARED)
>  		return kvmppc_share_page(kvm, gpa, page_shift);
>  
> -	ret = H_PARAMETER;
>  	srcu_idx = srcu_read_lock(&kvm->srcu);
> -	mmap_read_lock(kvm->mm);
>  
> -	start = gfn_to_hva(kvm, gfn);
> -	if (kvm_is_error_hva(start))
> -		goto out;
> -
> -	mutex_lock(&kvm->arch.uvmem_lock);
>  	/* Fail the page-in request of an already paged-in page */
> -	if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL))
> -		goto out_unlock;
> +	mutex_lock(&kvm->arch.uvmem_lock);
> +	ret = kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL);
> +	mutex_unlock(&kvm->arch.uvmem_lock);

Same comment as for the prev patch. I don't think you can release
the lock here.

> +	if (ret) {
> +		srcu_read_unlock(&kvm->srcu, srcu_idx);
> +		return H_PARAMETER;
> +	}
>  
> -	end = start + (1UL << page_shift);
> -	vma = find_vma_intersection(kvm->mm, start, end);
> -	if (!vma || vma->vm_start > start || vma->vm_end < end)
> -		goto out_unlock;
> +	do {
> +		ret = H_PARAMETER;
> +		mmap_read_lock(kvm->mm);
>  
> -	if (kvmppc_svm_migrate_page(vma, start, end, gpa, kvm, page_shift,
> -				true))
> -		goto out_unlock;
> +		start = gfn_to_hva(kvm, gfn);
> +		if (kvm_is_error_hva(start)) {
> +			mmap_read_unlock(kvm->mm);
> +			break;
> +		}
>  
> -	ret = H_SUCCESS;
> +		end = start + (1UL << page_shift);
> +		vma = find_vma_intersection(kvm->mm, start, end);
> +		if (!vma || vma->vm_start > start || vma->vm_end < end) {
> +			mmap_read_unlock(kvm->mm);
> +			break;
> +		}
> +
> +		mutex_lock(&kvm->arch.uvmem_lock);
> +		ret = kvmppc_svm_migrate_page(vma, start, end, gpa, kvm, page_shift, true);
> +		mutex_unlock(&kvm->arch.uvmem_lock);
> +
> +		mmap_read_unlock(kvm->mm);
> +	} while (ret == -2 && repeat_count--);
> +
> +	if (ret == -2)
> +		ret = H_BUSY;
>  
> -out_unlock:
> -	mutex_unlock(&kvm->arch.uvmem_lock);
> -out:
> -	mmap_read_unlock(kvm->mm);
>  	srcu_read_unlock(&kvm->srcu, srcu_idx);
>  	return ret;
>  }
> -- 
> 1.8.3.1