linux-kernel - Re: [PATCH V3] PCI: pciehp: Disable ACS Source Validation during hot-remove

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

Message-ID: <20240108141901.GA17779@wunner.de>
Date: Mon, 8 Jan 2024 15:19:01 +0100
From: Lukas Wunner <lukas@...ner.de>
To: Vidya Sagar <vidyas@...dia.com>
Cc: bhelgaas@...gle.com, alex.williamson@...hat.com, treding@...dia.com,
	jonathanh@...dia.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, vsethi@...dia.com, kthota@...dia.com,
	mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V3] PCI: pciehp: Disable ACS Source Validation during
 hot-remove

On Thu, Jan 04, 2024 at 08:01:06PM +0530, Vidya Sagar wrote:
> On 8/1/2023 1:29 AM, Lukas Wunner wrote:
> > As an alternative to disabling ACS, have you explored masking ACS
> > Violations (PCI_ERR_UNC_ACSV) upon de-enumeration of a device and
> > unmasking them after assignment of a bus number?
> 
> I explored this option and it seemed to work as expected. But, the issue
> is that this works only if the AER registers are owned by the OS. If the
> AER registers are owned by the firmware (i.e. Firmware-First approach of
> handling the errors), OS is not supposed to access the AER registers and
> there is no indication from the OS to the firmware as to when the
> enumeration is completed and time is apt to unmask the ACSViolation
> errors in the AER's Uncorrectable Error Mask register.
> Any thoughts on accommodating the Firmware-First approach also?

Are you actually using firmware-controlled AER or is it a theoretical
question?

PCI Firmware Spec r3.3 sec 4.6.12 talks about a _DSM to disable DPC
on surprise-hotplug-capable ports.  Maybe that would be an option?

BTW what happens if the system resumes from sleep and a device in
a hotplug-capable port doesn't have a bus number configured yet
(because it's been powered off and is now in D0uninitialized state)?
Could the ACS Violations then occur as well?  Do we have to mask
ACS Violations *generally* on Root Ports and Downstream Ports when
going to system sleep and unmask them after setting a bus number
in the attached device on resume?  And I suppose that would not
only be necessary for hotplug ports?

Thanks,

Lukas