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

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Date:   Wed, 17 Nov 2021 10:53:04 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     <abhsahu@...dia.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 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

> +}
> +
>  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++;