From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v6 2/5] dma-buf: heaps: Add heap helpers
Date: Thu, 18 Jul 2019 03:06:54 -0700
Message-ID: <20190718100654.GA19666@infradead.org>
References: <20190624194908.121273-1-john.stultz@linaro.org>
 <20190624194908.121273-3-john.stultz@linaro.org>
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> +void INIT_HEAP_HELPER_BUFFER(struct heap_helper_buffer *buffer,
> +			     void (*free)(struct heap_helper_buffer *))

Please use a lower case naming following the naming scheme for the
rest of the file.

> +static void *dma_heap_map_kernel(struct heap_helper_buffer *buffer)
> +{
> +	void *vaddr;
> +
> +	vaddr = vmap(buffer->pages, buffer->pagecount, VM_MAP, PAGE_KERNEL);
> +	if (!vaddr)
> +		return ERR_PTR(-ENOMEM);
> +
> +	return vaddr;
> +}

Unless I'm misreading the patches this is used for the same pages that
also might be dma mapped.  In this case you need to use
flush_kernel_vmap_range and invalidate_kernel_vmap_range in the right
places to ensure coherency between the vmap and device view.  Please
also document the buffer ownership, as this really can get complicated.

> +static vm_fault_t dma_heap_vm_fault(struct vm_fault *vmf)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +	struct heap_helper_buffer *buffer = vma->vm_private_data;
> +
> +	vmf->page = buffer->pages[vmf->pgoff];
> +	get_page(vmf->page);
> +
> +	return 0;
> +}

Is there any exlusion between mmap / vmap and the device accessing
the data?  Without that you are going to run into a lot of coherency
problems.