linux-kernel - Re: [RFC 2/3] vfio/pci: virtualize PME related registers bits and initialize to zero

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Date:   Thu, 18 Nov 2021 20:54:17 +0530
From:   Abhishek Sahu <abhsahu@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, Cornelia Huck <cohuck@...hat.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/3] vfio/pci: virtualize PME related registers bits and
 initialize to zero

On 11/17/2021 11:23 PM, Alex Williamson wrote:
> On Mon, 15 Nov 2021 19:06:39 +0530
> <abhsahu@...dia.com> wrote:
> 
>> From: Abhishek Sahu <abhsahu@...dia.com>
>>
>> If any PME event will be generated by PCI, then it will be mostly
>> handled in the host by the root port PME code. For example, in the case
>> of PCIe, the PME event will be sent to the root port and then the PME
>> interrupt will be generated. This will be handled in
>> drivers/pci/pcie/pme.c at the host side. Inside this, the
>> pci_check_pme_status() will be called where PME_Status and PME_En bits
>> will be cleared. So, the guest OS which is using vfio-pci device will
>> not come to know about this PME event.
>>
>> To handle these PME events inside guests, we need some framework so
>> that if any PME events will happen, then it needs to be forwarded to
>> virtual machine monitor. We can virtualize PME related registers bits
>> and initialize these bits to zero so vfio-pci device user will assume
>> that it is not capable of asserting the PME# signal from any power state.
>>
>> Signed-off-by: Abhishek Sahu <abhsahu@...dia.com>
>> ---
>>  drivers/vfio/pci/vfio_pci_config.c | 32 +++++++++++++++++++++++++++++-
>>  1 file changed, 31 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
>> index 6e58b4bf7a60..fb3a503a5b99 100644
>> --- a/drivers/vfio/pci/vfio_pci_config.c
>> +++ b/drivers/vfio/pci/vfio_pci_config.c
>> @@ -738,12 +738,27 @@ static int __init init_pci_cap_pm_perm(struct perm_bits *perm)
>>        */
>>       p_setb(perm, PCI_CAP_LIST_NEXT, (u8)ALL_VIRT, NO_WRITE);
>>
>> +     /*
>> +      * The guests can't process PME events. If any PME event will be
>> +      * generated, then it will be mostly handled in the host and the
>> +      * host will clear the PME_STATUS. So virtualize PME_Support bits.
>> +      * It will be initialized to zero later on.
>> +      */
>> +     p_setw(perm, PCI_PM_PMC, PCI_PM_CAP_PME_MASK, NO_WRITE);
>> +
>>       /*
>>        * Power management is defined *per function*, so we can let
>>        * the user change power state, but we trap and initiate the
>>        * change ourselves, so the state bits are read-only.
>> +      *
>> +      * The guest can't process PME from D3cold so virtualize PME_Status
>> +      * and PME_En bits. It will be initialized to zero later on.
>>        */
>> -     p_setd(perm, PCI_PM_CTRL, NO_VIRT, ~PCI_PM_CTRL_STATE_MASK);
>> +     p_setd(perm, PCI_PM_CTRL,
>> +            PCI_PM_CTRL_PME_ENABLE | PCI_PM_CTRL_PME_STATUS,
>> +            ~(PCI_PM_CTRL_PME_ENABLE | PCI_PM_CTRL_PME_STATUS |
>> +              PCI_PM_CTRL_STATE_MASK));
>> +
>>       return 0;
>>  }
>>
>> @@ -1412,6 +1427,18 @@ static int vfio_ext_cap_len(struct vfio_pci_core_device *vdev, u16 ecap, u16 epo
>>       return 0;
>>  }
>>
>> +static void vfio_update_pm_vconfig_bytes(struct vfio_pci_core_device *vdev,
>> +                                      int offset)
>> +{
>> +      /* initialize virtualized PME_Support bits to zero */
>> +     *(__le16 *)&vdev->vconfig[offset + PCI_PM_PMC] &=
>> +             ~cpu_to_le16(PCI_PM_CAP_PME_MASK);
>> +
>> +      /* initialize virtualized PME_Status and PME_En bits to zero */
> 
>         ^ Extra space here and above.
> 
> 
>> +     *(__le16 *)&vdev->vconfig[offset + PCI_PM_CTRL] &=
>> +             ~cpu_to_le16(PCI_PM_CTRL_PME_ENABLE | PCI_PM_CTRL_PME_STATUS);
> 
> Perhaps more readable and consistent with elsewhere as:
> 
>         __le16 *pmc = (__le16 *)&vdev->vconfig[offset + PCI_PM_PMC];
>         __le16 *ctrl = (__le16 *)&vdev->vconfig[offset + PCI_PM_CTRL];
> 
>         /* Clear vconfig PME_Support, PME_Status, and PME_En bits */
>         *pmc &= ~cpu_to_le16(PCI_PM_CAP_PME_MASK);
>         *ctrl &= ~cpu_to_le16(PCI_PM_CTRL_PME_ENABLE | PCI_PM_CTRL_PME_STATUS);
> 
> Thanks,
> Alex
> 

 Thanks Alex. I will fix this.

 Regards,
 Abhishek

>> +}
>> +
>>  static int vfio_fill_vconfig_bytes(struct vfio_pci_core_device *vdev,
>>                                  int offset, int size)
>>  {
>> @@ -1535,6 +1562,9 @@ static int vfio_cap_init(struct vfio_pci_core_device *vdev)
>>               if (ret)
>>                       return ret;
>>
>> +             if (cap == PCI_CAP_ID_PM)
>> +                     vfio_update_pm_vconfig_bytes(vdev, pos);
>> +
>>               prev = &vdev->vconfig[pos + PCI_CAP_LIST_NEXT];
>>               pos = next;
>>               caps++;
>