linux-kernel - Re: [PATCH 2/6] pci: Scan all functions when probing while running over Jailhouse

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Message-ID: <b830dc87-4953-835f-8479-fb57e55a035c@siemens.com>
Date:   Tue, 27 Feb 2018 08:25:45 +0100
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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 2/6] pci: Scan all functions when probing while running
 over Jailhouse

On 2018-02-22 21:57, Bjorn Helgaas wrote:
> On Mon, Jan 22, 2018 at 07:12:46AM +0100, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@...mens.com>
>>
>> PCI and PCIBIOS probing only scans devices at function number 0/8/16/...
>> Subdevices (e.g. multiqueue) have function numbers which are not a
>> multiple of 8.
> 
> Suggested text:
> 
>   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.
>   
>   This is technically prohibited by the spec, so it is possible that
>   PCI devices without the Multi-Function Device bit set may have
>   unexpected behavior in response to this probe.
> 
>> The simple hypervisor Jailhouse passes subdevices directly w/o providing
>> a virtual PCI topology like KVM. As a consequence a PCI passthrough from
>> Jailhouse to a guest will not be detected by Linux.
>>
>> Based on patch by Benedikt Spranger, adding Jailhouse probing to avoid
>> changing the behavior in the absence of the hypervisor.
>>
>> CC: Benedikt Spranger <b.spranger@...utronix.de>
>> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
> 
> With subject change to:
> 
>   PCI: Scan all functions when running over Jailhouse
> 
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> 

Thanks, all suggestions picked up for next round.

Jan

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