[PATCH] pci-assign: Do not reset the device unless the kernel supports it

Jan Kiszka
2011-06-06T21:32:18Z

From: Jan Kiszka <jan.kiszka@siemens.com>

At least kernels 2.6.38 and 2.6.39 do not properly support issuing a
reset on an assigned device and corrupt its config space. Prevent
this by checking for a host kernel with the required support, tagged by
the to-be-introduced KVM_CAP_DEVICE_RESET.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

PS: What's the state of those KVM patches? Will they make it into 3.0?

hw/device-assignment.c | 33 +++++++++++++++++++--------------
1 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 57d8dc0..97a1450 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -1689,26 +1689,31 @@ static const VMStateDescription vmstate_assigned_device = {
static void reset_assigned_device(DeviceState *dev)
{
PCIDevice *pci_dev = DO_UPCAST(PCIDevice, qdev, dev);
+#ifdef KVM_CAP_DEVICE_RESET
AssignedDevice *adev = DO_UPCAST(AssignedDevice, dev, pci_dev);
char reset_file[64];
const char reset[] = "1";
int fd, ret;

- snprintf(reset_file, sizeof(reset_file),
- "/sys/bus/pci/devices/%04x:%02x:%02x.%01x/reset",
- adev->host.seg, adev->host.bus, adev->host.dev, adev->host.func);
-
- /*
- * Issue a device reset via pci-sysfs. Note that we use write(2) here
- * and ignore the return value because some kernels have a bug that
- * returns 0 rather than bytes written on success, sending us into an
- * infinite retry loop using other write mechanisms.
- */
- fd = open(reset_file, O_WRONLY);
- if (fd != -1) {
- ret = write(fd, reset, strlen(reset));
- close(fd);
+ if (kvm_check_extension(kvm_state, KVM_CAP_DEVICE_RESET) {
+ snprintf(reset_file, sizeof(reset_file),
+ "/sys/bus/pci/devices/%04x:%02x:%02x.%01x/reset",
+ adev->host.seg, adev->host.bus, adev->host.dev,
+ adev->host.func);
+
+ /*
+ * Issue a device reset via pci-sysfs. Note that we use write(2) here
+ * and ignore the return value because some kernels have a bug that
+ * returns 0 rather than bytes written on success, sending us into an
+ * infinite retry loop using other write mechanisms.
+ */
+ fd = open(reset_file, O_WRONLY);
+ if (fd != -1) {
+ ret = write(fd, reset, strlen(reset));
+ close(fd);
+ }
}
+#endif /* KVM_CAP_DEVICE_RESET */

/*
* When a 0 is written to the command register, the device is logically