linux-kernel - Re: [PATCH v5 9/9] vfio/pci: Add dma-buf export support for MMIO regions

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Message-ID: <20251020164457.GQ6199@unreal>
Date: Mon, 20 Oct 2025 19:44:57 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: Alex Williamson <alex.williamson@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Christian König <christian.koenig@....com>,
	dri-devel@...ts.freedesktop.org, iommu@...ts.linux.dev,
	Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
	kvm@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, linux-mm@...ck.org,
	linux-pci@...r.kernel.org, Logan Gunthorpe <logang@...tatee.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH v5 9/9] vfio/pci: Add dma-buf export support for MMIO
 regions

On Mon, Oct 20, 2025 at 01:15:16PM -0300, Jason Gunthorpe wrote:
> On Fri, Oct 17, 2025 at 07:13:58PM +0300, Leon Romanovsky wrote:
> > > static int dma_ranges_to_p2p_phys(struct vfio_pci_dma_buf *priv,
> > > 				  struct vfio_device_feature_dma_buf *dma_buf,
> > > 				  struct vfio_region_dma_range *dma_ranges,
> > > 				  struct p2pdma_provider *provider)
> > > {
> > > 	struct pci_dev *pdev = priv->vdev->pdev;
> > > 	phys_addr_t len = pci_resource_len(pdev, dma_buf->region_index);
> > > 	phys_addr_t pci_start;
> > > 	phys_addr_t pci_last;
> > > 	u32 i;
> > > 
> > > 	if (!len)
> > > 		return -EINVAL;
> > > 	pci_start = pci_resource_start(pdev, dma_buf->region_index);
> > > 	pci_last = pci_start + len - 1;
> > > 	for (i = 0; i < dma_buf->nr_ranges; i++) {
> > > 		phys_addr_t last;
> > > 
> > > 		if (!dma_ranges[i].length)
> > > 			return -EINVAL;
> > > 
> > > 		if (check_add_overflow(pci_start, dma_ranges[i].offset,
> > > 				       &priv->phys_vec[i].paddr) ||
> > > 		    check_add_overflow(priv->phys_vec[i].paddr,
> > > 				       dma_ranges[i].length - 1, &last))
> > > 			return -EOVERFLOW;
> > > 		if (last > pci_last)
> > > 			return -EINVAL;
> > > 
> > > 		priv->phys_vec[i].len = dma_ranges[i].length;
> > > 		priv->size += priv->phys_vec[i].len;
> > > 	}
> > > 	priv->nr_ranges = dma_buf->nr_ranges;
> > > 	priv->provider = provider;
> > > 	return 0;
> > > }
> > 
> > I have these checks in validate_dmabuf_input(). 
> > Do you think that I need to add extra checks?
> 
> I think they work better in this function, so I'd move them here.

The main idea for validate_dmabuf_input() is to perform as much as
possible checks before allocating kernel memory.

Thanks

> 
> Jason