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

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Message-ID: <8adf7f98-3b05-2a76-48ec-111921219920@siemens.com>
Date:   Wed, 28 Feb 2018 11:01:05 +0100
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 2018-02-28 09:44, Thomas Gleixner wrote:
> 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.

Good point, and it also applies to pci_scan_child_bus_extend. Will add
some filters.

Jan

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