linux-kernel - Re: [patch RFC 23/38] x86/xen: Rework MSI teardown

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Date:   Mon, 24 Aug 2020 07:09:35 +0200
From:   Jürgen Groß <jgross@...e.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Joerg Roedel <joro@...tes.org>,
        iommu@...ts.linux-foundation.org, linux-hyperv@...r.kernel.org,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Jon Derrick <jonathan.derrick@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Wei Liu <wei.liu@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Steve Wahl <steve.wahl@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Russ Anderson <rja@....com>, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        xen-devel@...ts.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Megha Dey <megha.dey@...el.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Baolu Lu <baolu.lu@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [patch RFC 23/38] x86/xen: Rework MSI teardown

On 21.08.20 02:24, Thomas Gleixner wrote:
> X86 cannot store the irq domain pointer in struct device without breaking
> XEN because the irq domain pointer takes precedence over arch_*_msi_irqs()
> fallbacks.
> 
> XENs MSI teardown relies on default_teardown_msi_irqs() which invokes
> arch_teardown_msi_irq(). default_teardown_msi_irqs() is a trivial iterator
> over the msi entries associated to a device.
> 
> Implement this loop in xen_teardown_msi_irqs() to prepare for removal of
> the fallbacks for X86.
> 
> This is a preparatory step to wrap XEN MSI alloc/free into a irq domain
> which in turn allows to store the irq domain pointer in struct device and
> to use the irq domain functions directly.
> 
> Signed-off-by: Thomas Gleixner<tglx@...utronix.de>
> ---
>   arch/x86/pci/xen.c |   23 ++++++++++++++++++-----
>   1 file changed, 18 insertions(+), 5 deletions(-)
> 
> --- a/arch/x86/pci/xen.c
> +++ b/arch/x86/pci/xen.c
> @@ -376,20 +376,31 @@ static void xen_initdom_restore_msi_irqs
>   static void xen_teardown_msi_irqs(struct pci_dev *dev)
>   {
>   	struct msi_desc *msidesc;
> +	int i;
> +
> +	for_each_pci_msi_entry(msidesc, dev) {
> +		if (msidesc->irq) {
> +			for (i = 0; i < msidesc->nvec_used; i++)
> +				xen_destroy_irq(msidesc->irq + i);
> +		}
> +	}
> +}
> +
> +static void xen_pv_teardown_msi_irqs(struct pci_dev *dev)
> +{
> +	struct msi_desc *msidesc = first_pci_msi_entry(dev);
>   
> -	msidesc = first_pci_msi_entry(dev);
>   	if (msidesc->msi_attrib.is_msix)
>   		xen_pci_frontend_disable_msix(dev);
>   	else
>   		xen_pci_frontend_disable_msi(dev);
>   
> -	/* Free the IRQ's and the msidesc using the generic code. */
> -	default_teardown_msi_irqs(dev);
> +	xen_teardown_msi_irqs(dev);
>   }
>   
>   static void xen_teardown_msi_irq(unsigned int irq)
>   {
> -	xen_destroy_irq(irq);
> +	WARN_ON_ONCE(1);
>   }
>   
>   #endif
> @@ -412,7 +423,7 @@ int __init pci_xen_init(void)
>   #ifdef CONFIG_PCI_MSI
>   	x86_msi.setup_msi_irqs = xen_setup_msi_irqs;
>   	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
> -	x86_msi.teardown_msi_irqs = xen_teardown_msi_irqs;
> +	x86_msi.teardown_msi_irqs = xen_pv_teardown_msi_irqs;
>   	pci_msi_ignore_mask = 1;
>   #endif
>   	return 0;
> @@ -436,6 +447,7 @@ static void __init xen_hvm_msi_init(void
>   	}
>   
>   	x86_msi.setup_msi_irqs = xen_hvm_setup_msi_irqs;
> +	x86_msi.teardown_msi_irqs = xen_teardown_msi_irqs;
>   	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
>   }
>   #endif
> @@ -472,6 +484,7 @@ int __init pci_xen_initial_domain(void)
>   #ifdef CONFIG_PCI_MSI
>   	x86_msi.setup_msi_irqs = xen_initdom_setup_msi_irqs;
>   	x86_msi.teardown_msi_irq = xen_teardown_msi_irq;
> +	x86_msi.teardown_msi_irqs = xen_teardown_msi_irqs;

This should be xen_pv_teardown_msi_irqs, as pci_xen_initial_domain() is
called only for the pv initial domain case today.

>   	x86_msi.restore_msi_irqs = xen_initdom_restore_msi_irqs;
>   	pci_msi_ignore_mask = 1;
>   #endif
> 


Juergen