linux-kernel - Re: [PATCH v3] vfio_pci: Enable memory accesses before calling pci_map

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Date:   Tue, 19 Feb 2019 14:47:54 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v3] vfio_pci: Enable memory accesses before calling
 pci_map_rom

On Fri, 15 Feb 2019 17:16:06 +0100
Eric Auger <eric.auger@...hat.com> wrote:

> pci_map_rom/pci_get_rom_size() performs memory access in the ROM.
> In case the Memory Space accesses were disabled, readw() is likely
> to trigger a synchronous external abort on some platforms.
> 
> In case memory accesses were disabled, re-enable them before the
> call and disable them back again just after.
> 
> Fixes: 89e1f7d4c66d ("vfio: Add PCI device driver")
> 
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> Suggested-by: Alex Williamson <alex.williamson@...hat.com>

Applied to vfio next branch for v5.1.  Thanks,

Alex

> ---
> v2 -> v3:
> - follow Alex re-writing
> 
> v1 -> v2:
> - also re-enable in case of error
> ---
>  drivers/vfio/pci/vfio_pci.c | 25 +++++++++++++++++--------
>  1 file changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index ff60bd1ea587..4b0d30f1eabc 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -708,6 +708,7 @@ static long vfio_pci_ioctl(void *device_data,
>  		{
>  			void __iomem *io;
>  			size_t size;
> +			u16 orig_cmd;
>  
>  			info.offset = VFIO_PCI_INDEX_TO_OFFSET(info.index);
>  			info.flags = 0;
> @@ -723,15 +724,23 @@ static long vfio_pci_ioctl(void *device_data,
>  					break;
>  			}
>  
> -			/* Is it really there? */
> -			io = pci_map_rom(pdev, &size);
> -			if (!io || !size) {
> -				info.size = 0;
> -				break;
> -			}
> -			pci_unmap_rom(pdev, io);
> +			/*
> +			 * Is it really there?  Enable memory decode for
> +			 * implicit access in pci_map_rom().
> +			 */
> +			pci_read_config_word(pdev, PCI_COMMAND, &orig_cmd);
> +			pci_write_config_word(pdev, PCI_COMMAND,
> +					      orig_cmd | PCI_COMMAND_MEMORY);
>  
> -			info.flags = VFIO_REGION_INFO_FLAG_READ;
> +			io = pci_map_rom(pdev, &size);
> +			if (io) {
> +				info.flags = VFIO_REGION_INFO_FLAG_READ;
> +				pci_unmap_rom(pdev, io);
> +			} else {
> +				info.size = 0;
> +			}
> +
> +			pci_write_config_word(pdev, PCI_COMMAND, orig_cmd);
>  			break;
>  		}
>  		case VFIO_PCI_VGA_REGION_INDEX: