linux-kernel - Re: [PATCH] xen: xen-pciback: Reset MSI-X state when exposing a device

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Date:   Wed, 05 Dec 2018 09:26:32 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Chao Gao" <chao.gao@...el.com>
Cc:     "Roger Pau Monne" <roger.pau@...rix.com>,
        "Jia-Ju Bai" <baijiaju1990@...il.com>,
        "Stefano Stabellini" <sstabellini@...nel.org>,
        "xen-devel" <xen-devel@...ts.xenproject.org>,
        "Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
        "Juergen Gross" <jgross@...e.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen: xen-pciback: Reset MSI-X state when exposing
 a device

>>> On 05.12.18 at 03:19, <chao.gao@...el.com> wrote:
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -87,6 +87,55 @@ static struct pcistub_device *pcistub_device_alloc(struct pci_dev *dev)
>  	return psdev;
>  }
>  
> +/*
> + * Reset Xen internal MSI-X state by invoking PHYSDEVOP_{release, prepare}_msix.
> + */
> +int pcistub_msix_reset(struct pci_dev *dev)
> +{
> +#ifdef CONFIG_PCI_MSI
> +	if (dev->msix_cap) {
> +		struct physdev_pci_device ppdev = {
> +			.seg = pci_domain_nr(dev->bus),
> +			.bus = dev->bus->number,
> +			.devfn = dev->devfn
> +		};
> +		int err;
> +		u16 val;
> +
> +		/*
> +		 * Do a write first to flush Xen's internal state to hardware
> +		 * such that the following read can infer whether MSI-X maskall
> +		 * bit is set by Xen.
> +		 */
> +		pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &val);
> +		pci_write_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, val);
> +
> +		pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &val);
> +		if (!(val & PCI_MSIX_FLAGS_MASKALL))
> +			return 0;

I'm agreeing with prior comments: I don't see why you need
this conditional.

> +		pr_info("Reset MSI-X state for device %04x:%02x:%02x.%d\n",
> +			ppdev.seg, ppdev.bus, PCI_SLOT(ppdev.devfn),
> +			PCI_FUNC(ppdev.devfn));
> +
> +		err = HYPERVISOR_physdev_op(PHYSDEVOP_release_msix, &ppdev);
> +		if (err) {
> +			dev_warn(&dev->dev, "MSI-X release failed (%d)\n",
> +				 err);
> +			return err;
> +		}
> +
> +		err = HYPERVISOR_physdev_op(PHYSDEVOP_prepare_msix, &ppdev);
> +		if (err) {
> +			dev_err(&dev->dev, "MSI-X preparation failed (%d)\n",
> +				err);

Please can you make both log messages distinguishable from
the pre-existing ones, to aid diagnosis of possible probelms?

Jan