On 2/1/2022 1:41 AM, Alex Williamson wrote:
> On Mon, 31 Jan 2022 16:54:50 +0530
> Abhishek Sahu <abhsahu@xxxxxxxxxx> wrote:
>
>> If needs_pm_restore is set (PCI device does not have support for no
>> soft reset), then the current PCI state will be saved during D0->D3hot
>> transition and same will be restored back during D3hot->D0 transition.
>> For saving the PCI state locally, pci_store_saved_state() is being
>> used and the pci_load_and_free_saved_state() will free the allocated
>> memory.
>>
>> But for reset related IOCTLs, vfio driver calls PCI reset related
>> API's which will internally change the PCI power state back to D0. So,
>> when the guest resumes, then it will get the current state as D0 and it
>> will skip the call to vfio_pci_set_power_state() for changing the
>> power state to D0 explicitly. In this case, the memory pointed by
>> pm_save will never be freed. In a malicious sequence, the state changing
>> to D3hot followed by VFIO_DEVICE_RESET/VFIO_DEVICE_PCI_HOT_RESET can be
>> run in a loop and it can cause an OOM situation.
>>
>> Also, pci_pm_reset() returns -EINVAL if we try to reset a device that
>> isn't currently in D0. Therefore any path where we're triggering a
>> function reset that could use a PM reset and we don't know if the device
>> is in D0, should wake up the device before we try that reset.
>>
>> This patch changes the device power state to D0 by invoking
>> vfio_pci_set_power_state() before calling reset related API's.
>> It will help in fixing the mentioned memory leak and making sure
>> that the device is in D0 during reset. Also, to prevent any similar
>> memory leak for future development, this patch frees memory first
>> before overwriting 'pm_save'.
>>
>> Fixes: 51ef3a004b1e ("vfio/pci: Restore device state on PM transition")
>> Signed-off-by: Abhishek Sahu <abhsahu@xxxxxxxxxx>
>> ---
>>
>> * Changes in v2
>>
>> - Add the Fixes tag and sent this patch independently.
>> - Invoke vfio_pci_set_power_state() before invoking reset related API's.
>> - Removed saving of power state locally.
>> - Removed warning before 'kfree(vdev->pm_save)'.
>> - Updated comments and commit message according to updated changes.
>>
>> * v1 of this patch was sent in
>> https://lore.kernel.org/lkml/20220124181726.19174-4-abhsahu@xxxxxxxxxx/
>>
>> drivers/vfio/pci/vfio_pci_core.c | 27 +++++++++++++++++++++++++++
>> 1 file changed, 27 insertions(+)
>>
>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>> index f948e6cd2993..d6dd4f7c4b2c 100644
>> --- a/drivers/vfio/pci/vfio_pci_core.c
>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>> @@ -228,6 +228,13 @@ int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev, pci_power_t stat
>> if (!ret) {
>> /* D3 might be unsupported via quirk, skip unless in D3 */
>> if (needs_save && pdev->current_state >= PCI_D3hot) {
>> + /*
>> + * If somehow, the vfio driver was not able to free the
>> + * memory allocated in pm_save, then free the earlier
>> + * memory first before overwriting pm_save to prevent
>> + * memory leak.
>> + */
>> + kfree(vdev->pm_save);
>> vdev->pm_save = pci_store_saved_state(pdev);
>> } else if (needs_restore) {
>> pci_load_and_free_saved_state(pdev, &vdev->pm_save);
>> @@ -322,6 +329,12 @@ void vfio_pci_core_disable(struct vfio_pci_core_device *vdev)
>> /* For needs_reset */
>> lockdep_assert_held(&vdev->vdev.dev_set->lock);
>>
>> + /*
>> + * This function can be invoked while the power state is non-D0,
>> + * Change the device power state to D0 first.
>
> I think we need to describe more why we're doing this than what we're
> doing. We need to make sure the device is in D0 in case we have a
> reset method that depends on that directly, ex. pci_pm_reset(), or
> possibly device specific resets that may access device BAR resources.
> I think it's placed here in the function so that the config space
> changes below aren't overwritten by restoring the saved state and maybe
> also because the set_irqs_ioctl() call might access device MMIO space.
>
Thanks Alex.
I will add more details here in the comment.
>> + */
>> + vfio_pci_set_power_state(vdev, PCI_D0);
>> +
>> /* Stop the device from further DMA */
>> pci_clear_master(pdev);
>>
>> @@ -921,6 +934,13 @@ long vfio_pci_core_ioctl(struct vfio_device *core_vdev, unsigned int cmd,
>> return -EINVAL;
>>
>> vfio_pci_zap_and_down_write_memory_lock(vdev);
>> +
>> + /*
>> + * This function can be invoked while the power state is non-D0,
>> + * Change the device power state to D0 before doing reset.
>> + */
>
> See below, reconsidering this...
>
>> + vfio_pci_set_power_state(vdev, PCI_D0);
>> +
>> ret = pci_try_reset_function(vdev->pdev);
>> up_write(&vdev->memory_lock);
>>
>> @@ -2055,6 +2075,13 @@ static int vfio_pci_dev_set_hot_reset(struct vfio_device_set *dev_set,
>> }
>> cur_mem = NULL;
>>
>> + /*
>> + * This function can be invoked while the power state is non-D0.
>> + * Change power state of all devices to D0 before doing reset.
>> + */
>
> Here I have trouble convincing myself exactly what we're doing. As you
> note in patch 1/ of the RFC series, pci_reset_bus(), or more precisely
> pci_dev_save_and_disable(), wakes the device to D0 before reset, so we
> can't be doing this only to get the device into D0. The function level
> resets do the same.
>
> Actually, now I'm remembering and debugging where I got myself confused
> previously with pci_pm_reset(). The scenario was a Windows guest with
> an assigned Intel 82574L NIC. When doing a shutdown from the guest the
> device is placed in D3hot and we enter vfio_pci_core_disable() in that
> state. That function however uses __pci_reset_function_locked(), which
> skips the pci_dev_save_and_disable() since much of it is redundant for
> that call path (I think I generalized this to all flavors of
> pci_reset_function() in my head).
Thanks for providing the background related with the original issue.
>
> The standard call to pci_try_reset_function(), as in the previous
> chunk, will make use of pci_dev_save_and_disable(), so for either of
> these latter cases the concern cannot be simply having the device in D0,
> we need a reason that we want the previously saved state restored on the
> device before the reset, and thus restored to the device after the
> reset as the rationale for the change.
>
I will add this as a comment.
>> + list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list)
>> + vfio_pci_set_power_state(cur, PCI_D0);
>> +
>> ret = pci_reset_bus(pdev);
>>
>> err_undo:
>
>
> We also call pci_reset_bus() in vfio_pci_dev_set_try_reset(). In that
> case, none of the other devices can be in use by the user, but they can
> certainly be in D3hot with previous device state saved off into our
> pm_save cache. If we don't have a good reason to restore in that case,
> I'm wondering if we really have a good reason to restore in the above
> two cases.
>
> Perhaps we just need the first chunk above to resolve the memory leak,
First chunk means only the changes done in vfio_pci_set_power_state()
which is calling kfree() before calling pci_store_saved_state().
Or I need to include more things in the first patch ?
With the kfree(), the original memory leak issue should be solved.
> and the second chunk as a separate patch to resolve the issue with
> devices entering vfio_pci_core_disable() in non-D0 state. Sorry if I
And this second patch will contain rest of the things where
we will call vfio_pci_set_power_state() explicitly for moving to
D0 state ?
Also, We need to explore if setting to D0 state is really required at
all these places and If it is not required, then we don't need second
patch ?
Thanks,
Abhishek
> mislead you that we had a more widespread issue with pci_pm_reset(), it
> wasn't clear in my head until now that it was only the
> __pci_reset_function_locked() caller that had the issue. Thanks,
>
> Alex
>
