linux-kernel - Re: [RFC PATCH] vfio/pci: Allow force needs_pm

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Date:   Wed, 25 Nov 2020 08:53:12 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Colin Xu <colin.xu@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        swee.yee.fonn@...el.com
Subject: Re: [RFC PATCH] vfio/pci: Allow force needs_pm_restore as specified
 by device:vendor

On Wed, 25 Nov 2020 10:18:24 +0800
Colin Xu <colin.xu@...el.com> wrote:

> Force specific device listed in params pm_restore_ids to follow
> device state save/restore as needs_pm_restore.
> Some device has NoSoftRst so will skip current state save/restore enabled
> by needs_pm_restore. However once the device experienced power state
> D3<->D0 transition, either by idle_d3 or the guest driver changes PM_CTL,
> the guest driver won't get correct devie state although the configure
> space doesn't change.

It sounds like you're describing a device that incorrectly exposes
NoSoftRst when there is in fact some sort of internal reset that
requires reprogramming config space.  What device requires this?  How
is a user to know when this option is required?  It seems like this
would be better handled via a quirk in PCI core that sets a device flag
that the NoSoftRst value is incorrect for the specific affected
devices.  Thanks,

Alex


> 
> Cc: Swee Yee Fonn <swee.yee.fonn@...el.com>
> Signed-off-by: Colin Xu <colin.xu@...el.com>
> ---
>  drivers/vfio/pci/vfio_pci.c | 66 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 65 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index e6190173482c..50a4141c9e1d 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -34,6 +34,15 @@
>  #define DRIVER_AUTHOR   "Alex Williamson <alex.williamson@...hat.com>"
>  #define DRIVER_DESC     "VFIO PCI - User Level meta-driver"
>  
> +#define VFIO_MAX_PM_DEV 32
> +struct vfio_pm_devs {
> +	struct {
> +		unsigned short  vendor;
> +		unsigned short  device;
> +	} ids[VFIO_MAX_PM_DEV];
> +	u32 count;
> +};
> +
>  static char ids[1024] __initdata;
>  module_param_string(ids, ids, sizeof(ids), 0);
>  MODULE_PARM_DESC(ids, "Initial PCI IDs to add to the vfio driver, format is \"vendor:device[:subvendor[:subdevice[:class[:class_mask]]]]\" and multiple comma separated entries can be specified");
> @@ -64,6 +73,10 @@ static bool disable_denylist;
>  module_param(disable_denylist, bool, 0444);
>  MODULE_PARM_DESC(disable_denylist, "Disable use of device denylist. Disabling the denylist allows binding to devices with known errata that may lead to exploitable stability or security issues when accessed by untrusted users.");
>  
> +static char pm_restore_ids[1024] __initdata;
> +module_param_string(pm_restore_ids, pm_restore_ids, sizeof(pm_restore_ids), 0);
> +MODULE_PARM_DESC(pm_restore_ids, "comma separated device in format of \"vendor:device\"");
> +
>  static inline bool vfio_vga_disabled(void)
>  {
>  #ifdef CONFIG_VFIO_PCI_VGA
> @@ -260,10 +273,50 @@ static bool vfio_pci_nointx(struct pci_dev *pdev)
>  	return false;
>  }
>  
> +static struct vfio_pm_devs pm_devs = {0};
> +static void __init vfio_pci_fill_pm_ids(void)
> +{
> +	char *p, *id;
> +	int idx = 0;
> +
> +	/* no ids passed actually */
> +	if (pm_restore_ids[0] == '\0')
> +		return;
> +
> +	/* add ids specified in the module parameter */
> +	p = pm_restore_ids;
> +	while ((id = strsep(&p, ","))) {
> +		unsigned int vendor, device = PCI_ANY_ID;
> +		int fields;
> +
> +		if (!strlen(id))
> +			continue;
> +
> +		fields = sscanf(id, "%x:%x", &vendor, &device);
> +
> +		if (fields != 2) {
> +			pr_warn("invalid vendor:device string \"%s\"\n", id);
> +			continue;
> +		}
> +
> +		if (idx < VFIO_MAX_PM_DEV) {
> +			pm_devs.ids[idx].vendor = vendor;
> +			pm_devs.ids[idx].device = device;
> +			pm_devs.count++;
> +			idx++;
> +			pr_info("add [%04x:%04x] for needs_pm_restore\n",
> +				vendor, device);
> +		} else {
> +			pr_warn("Exceed maximum %d, skip adding [%04x:%04x] for needs_pm_restore\n",
> +				VFIO_MAX_PM_DEV, vendor, device);
> +		}
> +	}
> +}
> +
>  static void vfio_pci_probe_power_state(struct vfio_pci_device *vdev)
>  {
>  	struct pci_dev *pdev = vdev->pdev;
> -	u16 pmcsr;
> +	u16 pmcsr, idx;
>  
>  	if (!pdev->pm_cap)
>  		return;
> @@ -271,6 +324,16 @@ static void vfio_pci_probe_power_state(struct vfio_pci_device *vdev)
>  	pci_read_config_word(pdev, pdev->pm_cap + PCI_PM_CTRL, &pmcsr);
>  
>  	vdev->needs_pm_restore = !(pmcsr & PCI_PM_CTRL_NO_SOFT_RESET);
> +
> +	for (idx = 0; idx < pm_devs.count; idx++) {
> +		if (vdev->pdev->vendor == pm_devs.ids[idx].vendor &&
> +		    vdev->pdev->device == pm_devs.ids[idx].device) {
> +			vdev->needs_pm_restore = true;
> +			pr_info("force [%04x:%04x] to needs_pm_restore\n",
> +				vdev->pdev->vendor, vdev->pdev->device);
> +			break;
> +		}
> +	}
>  }
>  
>  /*
> @@ -2423,6 +2486,7 @@ static int __init vfio_pci_init(void)
>  		goto out_driver;
>  
>  	vfio_pci_fill_ids();
> +	vfio_pci_fill_pm_ids();
>  
>  	if (disable_denylist)
>  		pr_warn("device denylist disabled.\n");