linux-kernel - Re: [RFC PATCH v3 5/5] vfio-pci: Allow to mmap MSI-X table if host bridge supports filtering of MSIs

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Date:	Thu, 28 Jan 2016 15:46:28 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Yongji Xie <xyjxie@...ux.vnet.ibm.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-doc@...r.kernel.org
Cc:	bhelgaas@...gle.com, corbet@....net, aik@...abs.ru,
	benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
	warrier@...ux.vnet.ibm.com, zhong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com
Subject: Re: [RFC PATCH v3 5/5] vfio-pci: Allow to mmap MSI-X table if host
 bridge supports filtering of MSIs

On Fri, 2016-01-15 at 15:06 +0800, Yongji Xie wrote:
> Current vfio-pci implementation disallows to mmap MSI-X
> table in case that user get to touch this directly.
> 
> But we should allow to mmap these MSI-X tables if the PCI
> host bridge supports filtering of MSIs.
> 
> Signed-off-by: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
> ---
>  drivers/vfio/pci/vfio_pci.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 11fd0f0..4d68f6a 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -555,7 +555,8 @@ static long vfio_pci_ioctl(void *device_data,
>  			    IORESOURCE_MEM && !pci_resources_share_page(pdev,
>  			    info.index)) {
>  				info.flags |= VFIO_REGION_INFO_FLAG_MMAP;
> -				if (info.index == vdev->msix_bar) {
> +				if (!pci_host_bridge_msi_filtered_enabled(pdev) &&
> +				    info.index == vdev->msix_bar) {
>  					ret = msix_sparse_mmap_cap(vdev, &caps);
>  					if (ret)
>  						return ret;
> @@ -967,7 +968,8 @@ static int vfio_pci_mmap(void *device_data, struct vm_area_struct *vma)
>  	if (phys_len < PAGE_SIZE || req_start + req_len > phys_len)
>  		return -EINVAL;
>  
> -	if (index == vdev->msix_bar) {
> +	if (!pci_host_bridge_msi_filtered_enabled(pdev) &&
> +	    index == vdev->msix_bar) {
>  		/*
>  		 * Disallow mmaps overlapping the MSI-X table; users don't
>  		 * get to touch this directly.  We could find somewhere

What about read()/write() access, why would we allow mmap() but not
those?