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

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Message-Id: <20190213101406.3934-1-eric.auger@redhat.com>
Date:   Wed, 13 Feb 2019 11:14:06 +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] 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
crash the host with a synchronous external abort (aarch64).

In case memory accesses were disabled, re-enable them before the call
and disable them back again just after.

Signed-off-by: Eric Auger <eric.auger@...hat.com>
---
 drivers/vfio/pci/vfio_pci.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index ff60bd1ea587..96b8bbd909d7 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -706,8 +706,10 @@ static long vfio_pci_ioctl(void *device_data,
 			break;
 		case VFIO_PCI_ROM_REGION_INDEX:
 		{
+			bool mem_access_disabled;
 			void __iomem *io;
 			size_t size;
+			u16 cmd;
 
 			info.offset = VFIO_PCI_INDEX_TO_OFFSET(info.index);
 			info.flags = 0;
@@ -723,6 +725,13 @@ static long vfio_pci_ioctl(void *device_data,
 					break;
 			}
 
+			pci_read_config_word(pdev, PCI_COMMAND, &cmd);
+			mem_access_disabled = !(cmd & PCI_COMMAND_MEMORY);
+			if (mem_access_disabled) {
+				cmd |= PCI_COMMAND_MEMORY;
+				pci_write_config_word(pdev, PCI_COMMAND, cmd);
+			}
+
 			/* Is it really there? */
 			io = pci_map_rom(pdev, &size);
 			if (!io || !size) {
@@ -731,6 +740,11 @@ static long vfio_pci_ioctl(void *device_data,
 			}
 			pci_unmap_rom(pdev, io);
 
+			if (mem_access_disabled) {
+				cmd &= ~PCI_COMMAND_MEMORY;
+				pci_write_config_word(pdev, PCI_COMMAND, cmd);
+			}
+
 			info.flags = VFIO_REGION_INFO_FLAG_READ;
 			break;
 		}
-- 
2.20.1