linux-kernel - Re: [PATCH v2 8/9] PCI: Exclude PCIe ports used for tunneling in pcie_bandwidth

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20231107062405.GU17433@black.fi.intel.com>
Date:   Tue, 7 Nov 2023 08:24:05 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Mario Limonciello <mario.limonciello@....com>,
        Karol Herbst <kherbst@...hat.com>,
        Lyude Paul <lyude@...hat.com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Danilo Krummrich <dakr@...hat.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Xinhui Pan <Xinhui.Pan@....com>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Mark Gross <markgross@...nel.org>,
        Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        Pali Rohár <pali@...nel.org>,
        Marek Behún <kabel@...nel.org>,
        "Maciej W . Rozycki" <macro@...am.me.uk>,
        Manivannan Sadhasivam <mani@...nel.org>,
        "open list:DRM DRIVER FOR NVIDIA GEFORCE/QUADRO GPUS" 
        <dri-devel@...ts.freedesktop.org>,
        "open list:DRM DRIVER FOR NVIDIA GEFORCE/QUADRO GPUS" 
        <nouveau@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:RADEON and AMDGPU DRM DRIVERS" 
        <amd-gfx@...ts.freedesktop.org>,
        "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
        "open list:ACPI" <linux-acpi@...r.kernel.org>,
        "open list:X86 PLATFORM DRIVERS" 
        <platform-driver-x86@...r.kernel.org>,
        "open list:THUNDERBOLT DRIVER" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v2 8/9] PCI: Exclude PCIe ports used for tunneling in
 pcie_bandwidth_available()

On Tue, Nov 07, 2023 at 07:45:26AM +0200, Mika Westerberg wrote:
> Hi,
> 
> On Mon, Nov 06, 2023 at 07:56:52PM +0100, Lukas Wunner wrote:
> > On Mon, Nov 06, 2023 at 12:44:25PM -0600, Mario Limonciello wrote:
> > > Tangentially related; the link speed is currently symmetric but there are
> > > two sysfs files.  Mika left a comment in drivers/thunderbolt/switch.c it may
> > > be asymmetric in the future. So we may need to keep that in mind on any
> > > design that builds on top of them.
> > 
> > Aren't asymmetric Thunderbolt speeds just a DisplayPort thing?
> 
> No, they affect the whole fabric. We have the initial code for
> asymmetric switching in v6.7-rc1.
> 
> > > As 'thunderbolt' can be a module or built in, we need to bring code into PCI
> > > core so that it works in early boot before it loads.
> > 
> > tb_switch_get_generation() is small enough that it could be moved to the
> > PCI core.  I doubt that we need to make thunderbolt built-in only
> > or move a large amount of code to the PCI core.
> 
> If at all possible I would like to avoid this and littering PCI side
> with non-PCI stuff. There could be other similar "mediums" in the future
> where you can transfer packets of "native" protocols such as PCIe so
> instead of making it Thunderbolt/USB4 specific it should be generic
> enough to support future extensions.
> 
> In case of Thunderbolt/USB4 there is no real way to figure out how much
> bandwidth each PCIe tunnel gets (it is kind of bulk traffic that gets
> what is left from isochronous protocols) so I would not even try that
> and instead use the real PCIe links in pcie_bandwidth_available() and
> skip all the "virtual" ones.

Actually can we call the new function something like pci_link_is_virtual()
instead and make pcie_bandwidth_available() call it? That would be more
future proof IMHO.