linux-kernel - Re: [PATCH v2 2/6] PCI: Scan all functions when running over Jailhouse

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Message-ID: <alpine.DEB.2.21.1802280938380.1886@nanos.tec.linutronix.de>
Date:   Wed, 28 Feb 2018 09:44:12 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jan Kiszka <jan.kiszka@...mens.com>
cc:     Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, x86@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        jailhouse-dev@...glegroups.com, linux-pci@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        Benedikt Spranger <b.spranger@...utronix.de>
Subject: Re: [PATCH v2 2/6] PCI: Scan all functions when running over
 Jailhouse

On Wed, 28 Feb 2018, Jan Kiszka wrote:

> From: Jan Kiszka <jan.kiszka@...mens.com>
> 
> Per PCIe r4.0, sec 7.5.1.1.9, multi-function devices are required to
> have a function 0.  Therefore, Linux scans for devices at function 0
> (devfn 0/8/16/...) and only scans for other functions if function 0
> has its Multi-Function Device bit set or ARI or SR-IOV indicate
> there are more functions.
> 
> The Jailhouse hypervisor may pass individual functions of a
> multi-function device to a guest without passing function 0, which
> means a Linux guest won't find them.
> 
> Change Linux PCI probing so it scans all function numbers when
> running as a guest over Jailhouse.

>  void pcibios_scan_specific_bus(int busn)
>  {
> +	int stride = jailhouse_paravirt() ? 1 : 8;
>  	int devfn;
>  	u32 l;
>  
>  	if (pci_find_bus(0, busn))
>  		return;
>  
> -	for (devfn = 0; devfn < 256; devfn += 8) {
> +	for (devfn = 0; devfn < 256; devfn += stride) {
>  		if (!raw_pci_read(0, busn, devfn, PCI_VENDOR_ID, 2, &l) &&
>  		    l != 0x0000 && l != 0xffff) {
>  			DBG("Found device at %02x:%02x [%04x]\n", busn, devfn, l);

Shouldn't that take the situation into account where the MFD bit is set on
a regular devfn, i.e. (devfn % 8) == 0? In that case you'd scan the
subfunctions twice.

Thanks,

	tglx