[libvirt] [PATCH] virpci:fix Secondary Bus Reset bug

[Laine Stump]

The fact that you are modifying this code implies that you are using it, 
and that implies that you are still using legacy KVM device assignment 
(i.e. the pcistub driver) instead of VFIO device assignment. (I say this 
because the function that calls this function you've patched, 
virPCIDeviceReset(), has a check very early on that short-circuits the 
entire function if the device is bound to vfio-pci (and if the device is 
bound to a host driver, then you shouldn't be resetting it anyway, so 
the only reason it would be executed is if you're using legacy KVM 
device assignment or are calling virsh nodedev-reset when you shouldn't).

Legacy PCI device assignment was deprecated over 5 years ago, and was 
removed from the kernel sometime after that. We are seriously 
considering removing all vestigal support for legacy KVM device 
assignment from libvirt, since any kernel that is less than 5 years old 
have VFIO, and most don't even support legacy KVM device assignment at all.

So are you actually using legacy KVM device assignment, or did you just 
find this bug by manual code inspection? If the latter, then you need to 
seriously look into using VFIO instead. If the latter, then this patch 
can safely be pushed, but it's not going to actually do anything (and 
the code it's in will likely no longer exist within the next 6 months).

On 8/15/19 5:44 AM, hexin900110 at 163.com wrote:
> From: hexin <hexin15 at baidu.com>
>
> The parent bridge configuration of the current device
> should be read and reset, instead of reading the current
> device configuration.
>
> Signed-off-by: He Xin <hexin15 at baidu.com>
> Signed-off-by: Liu Qi <liuqi16 at baidu.com>
> Signed-off-by: Zhang Yu <zhangyu31 at baidu.com>
> ---
>   src/util/virpci.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/util/virpci.c b/src/util/virpci.c
> index 61a6b359e5..483de2cb16 100644
> --- a/src/util/virpci.c
> +++ b/src/util/virpci.c
> @@ -821,7 +821,7 @@ virPCIDeviceTrySecondaryBusReset(virPCIDevicePtr dev,
>       /* Read the control register, set the reset flag, wait 200ms,
>        * unset the reset flag and wait 200ms.
>        */
> -    ctl = virPCIDeviceRead16(dev, cfgfd, PCI_BRIDGE_CONTROL);
> +    ctl = virPCIDeviceRead16(dev, parentfd, PCI_BRIDGE_CONTROL);
>   
>       virPCIDeviceWrite16(parent, parentfd, PCI_BRIDGE_CONTROL,
>                           ctl | PCI_BRIDGE_CTL_RESET);