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

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-06-07 20:46, Alex Williamson wrote:
> On Tue, 2011-06-07 at 10:14 +0200, Jan Kiszka wrote:
>> On 2011-06-07 10:06, Avi Kivity wrote:
>>> On 06/07/2011 01:04 AM, Jan Kiszka wrote:
>>>> On 2011-06-06 23:48, Alex Williamson wrote:
>>>>>  On Mon, 2011-06-06 at 23:30 +0200, Jan Kiszka wrote:
>>>>>>  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.
>>>>>
>>>>>  Wouldn't it be easier just to revert ed78661f in 2.6.39 stable?  I
>>>> guess
>>>>>  we don't have an option to do that for .38 since stable is done there,
>>>>>  but there are also some intel-iommu breakages that won't make
>>>> stable for
>>>>>  that release.  It seems like the userspace invoked reset resolves
>>>> known,
>>>>>  demonstrable issues of devices continuing to DMA into guest memory
>>>> while
>>>>>  ed78661f is mostly a theoretical change.
>>>>
>>>> Easier would be this patch. But I don't mind reverting the problematic
>>>> commit in 39, whatever is preferred. We should just resolve the issue
>>>> finally.
>>>
>>> Kernel problems should be solved in the kernel (with exceptions of
>>> course, but don't see the need here).
>>
>> Then please file a revert for stable ASAP.
> 
> How's this?  For stable only or course.  Thanks,
> 
> Alex
> 
> Revert "KVM: Save/restore state of assigned PCI device"
> 
> From: Alex Williamson <alex.williamson@redhat.com>
> 
> This reverts ed78661f2614d3c9f69c23e280db3bafdabdf5bb as it assumes
> the saved PCI state will remain valid for the entire length of time
> that it is attached to a guest.  This fails when userspace makes use
> of the pci-sysfs reset interface, which invalidates the saved device
> state, leaving nothing to be restored after the device is reset on
> de-assignment.  This leaves the device in an unusable state.
> 
> 3.0.0 will add an interface for KVM to save the PCI state in a

[ It will be called "3.0". :) ]

> buffer unaffected by other callers of pci_reset_function(), but the
> most appropriate stable fix seems to be reverting this change since
> the original assumption about the device saved state persisting is
> incorrect.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
> 
>  virt/kvm/assigned-dev.c |    5 +----
>  1 files changed, 1 insertions(+), 4 deletions(-)
> 
> 
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index ae72ae6..e3f1235 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -197,8 +197,7 @@ static void kvm_free_assigned_device(struct kvm *kvm,
>  {
>  	kvm_free_assigned_irq(kvm, assigned_dev);
>  
> -	__pci_reset_function(assigned_dev->dev);
> -	pci_restore_state(assigned_dev->dev);
> +	pci_reset_function(assigned_dev->dev);
>  
>  	pci_release_regions(assigned_dev->dev);
>  	pci_disable_device(assigned_dev->dev);
> @@ -515,7 +514,6 @@ static int kvm_vm_ioctl_assign_device(struct kvm *kvm,
>  	}
>  
>  	pci_reset_function(dev);
> -	pci_save_state(dev);
>  
>  	match->assigned_dev_id = assigned_dev->assigned_dev_id;
>  	match->host_segnr = assigned_dev->segnr;
> @@ -546,7 +544,6 @@ out:
>  	mutex_unlock(&kvm->lock);
>  	return r;
>  out_list_del:
> -	pci_restore_state(dev);
>  	list_del(&match->list);
>  	pci_release_regions(dev);
>  out_disable:
> 
> 
> 

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

Jan


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