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

Jan Kiszka
2011-06-08T07:52:17Z

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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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