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

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Message-Id: <20190215161606.32334-1-eric.auger@redhat.com>
Date:   Fri, 15 Feb 2019 17:16:06 +0100
From:   Eric Auger <eric.auger@...hat.com>
To:     eric.auger.pro@...il.com, eric.auger@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        alex.williamson@...hat.com
Subject: [PATCH v3] vfio_pci: Enable memory accesses before calling pci_map_rom

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>

---
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:
-- 
2.20.1