Re: [RFC PATCH 0/9] Add RAS support for CXL root ports, CXL downstream switch ports, and CXL upstream switch ports

[Fan Ni <nifan.cxl@gmail.com>]

On Mon, Aug 19, 2024 at 11:21:01AM -0500, Terry Bowman wrote:
> Hi Fan
> 
> On 7/25/24 13:49, fan wrote:
> > On Mon, Jun 17, 2024 at 03:04:02PM -0500, Terry Bowman wrote:
> >> This patchset provides RAS logging for CXL root ports, CXL downstream
> >> switch ports, and CXL upstream switch ports. This includes changes to
> >> use a portdrv notifier chain to communicate CXL AER/RAS errors to a
> >> cxl_pci callback.
> >>
> >> The first 3 patches prepare for and add an atomic notifier chain to the
> >> portdrv driver. The portdrv's notifier chain reports the port device's
> >> AER internal errors to the registered callback(s). The preparation changes
> >> include a portdrv update to call the uncorrectable handler for PCIe root
> >> ports and PCIe downstream switch ports. Also, the AER correctable error
> >> (CE) status is made available to the AER CE handler.
> >>
> >> The next 4 patches are in preparation for adding an atomic notification
> >> callback in the cxl_pci driver. This is for receiving AER internal error
> >> events from the portdrv notifier chain. Preparation includes adding RAS
> >> register block mapping, adding trace functions for logging, and
> >> refactoring cxl_pci RAS functions for reuse.
> >>
> >> The final 2 patches enable the AER internal error interrupts.
> >>
> >> Testing RAS CE/UCE:
> >>   QEMU was used for testing CXL root port, CXL downstream switch port, and
> >>   CXL upstream switch port. The aer-inject tool was used to inject AER and
> >>   a test patch was used to set the AER CIE/UIE and RAS CE/UCE status during
> >>   testing. Testing passed with no issues.
> > 
> > Hi Terry,
> > 
> > Could you share a little more about the qemu test setup?
> > From what I see, it seems currently qemu can only inject error to
> > type3 devices, is that true? Or how to do that for port devices?
> > Do we need a hack there?
> > 
> > Also, is the aer-inject tool you mentioned the one currently in the kernel
> > or something else?
> > https://elixir.bootlin.com/linux/v6.10-rc6/source/drivers/pci/pcie/aer_inject.c
> > 
> > Thanks,
> > Fan
> > 
> Sorry for the late response.
> 
> I used AMD RAS injection for testing HW root ports.
> 
> I used QEMU and the legacy aer-inject userspace tool to test switch ports (USP/DSP).[1] 
> I added a couple test patches to set the AER UIE/CIE because the tool doesn't support 
> injecting UIE or CIE bits. I used a test patch for assigning the RAS status as well.
> 
> Regards,
> Terry
> 
> [1] - https://git.kernel.org/pub/scm/linux/kernel/git/gong.chen/aer-inject.git/about/
> 

Hi Terry,
Thanks for the reply. I was able to do aer error inject through the aer
inject kernel module and the user space tool. 
Trying to exercise the code in this patchset.

Fan

> > 
> >>  
> >>   An AMD platform with the AMD RAS error injection tool was used for
> >>   testing CXL root port injection. Testing passed with no issues.
> >>
> >>   TODO - regression test CXL1.1 RCH handling.
> >>
> >> Solutions Considered (1-4):
> >>   Below are solutions that were considered. Solution #4 is
> >>   implemented in this patchset. 
> >>
> >>   1.) Reassigning portdrv error handler for CXL port devices
> >>   
> >>   This solution was based on reassigning the portdrv's CE/UCE err_handler
> >>   to be CXL cxl_pci driver functions.
> >>   
> >>   I started with this solution and once the flow was working I realized
> >>   the endpoint removal would have to be addressed as well. While this
> >>   could be resolved it does highlight the odd coupling and dependency
> >>   between the CXL port devices error handling with cxl_pci endpoint's
> >>   handlers. Also, the err_handler re-assignment at runtime required
> >>   ignoring the 'const' definition. I don't believe this should be
> >>   considered as a possible solution.
> >>   
> >>   2.) Update the AER driver to call cxl_pci driver's error handler before
> >>   calling pci_aer_handle_error()
> >>
> >>   This is similar to the existing RCH port error approach in aer.c.
> >>   In this solution the AER driver searches for a downstream CXL endpoint
> >>   to 'handle' detected CXL port protocol errors.
> >>
> >>   This is a good solution to consider if the one presented in this patchset
> >>   is not acceptable. I was initially reluctant to this approach because it
> >>   adds more CXL coupling to the AER driver. But, I think this solution
> >>   would technically work. I believe Ming was working towards this
> >>   solution.
> >>
> >>   3.) Refactor portdrv
> >>   The portdrv refactoring solution is to change the portdrv service drivers
> >>   into PCIe auxiliary drivers. With this change the facility drivers can be
> >>   associated with a PCIe driver instead fixed bound to the portdrv driver.
> >>
> >>   In this case the CXL port functionality would be added either as a CXL
> >>   auxiliary driver or as a CXL specific port driver
> >>   (PCI_CLASS_BRIDGE_PCI_NORMAL).
> >>
> >>   This solution has challenges in the interrupt allocation by separate
> >>   auxiliary drivers and in binding of a specific driver. Binding is
> >>   currently based on PCIe class and would require extending the binding
> >>   logic to support multiple drivers for the same class.
> >>
> >>   Jonathan Cameron is working towards this solution by initially solving
> >>   for the PMU service driver.[1] It is using the auxiliary bus to associate
> >>   what were service drivers with the portdrv driver. Using a CXL auxiliary
> >>   for handling CXL port RAS errors would result in RAS logic called from
> >>   the cxl_pci and CXL auxiliary drivers. This may need a library driver.
> >>
> >>   4.) Using a portdrv notifier chain/callback for CIE/UIE
> >>   (Implemented in this patchset)
> >>
> >>   This solution uses a portdrv atomic chain notifier and a cxl_pci
> >>   callback to handle and log CXL port RAS errors.
> >>   
> >>   I chose this after trying solution#1 above. I see a couple advantages to
> >>   this solution are:
> >>   - Is general port implementation for CIE/UIE specific handling mentioned
> >>   in the PCIe spec.[2]
> >>   - Notifier is used in RAS MCE driver as an existing example.
> >>   - Does not introduce further CXL dependencies into the AER driver.
> >>   - The notifier chain provides registration/unregistration and
> >>   synchronization.
> >>
> >>   A disadvantage of this approach is coupling still exists between the CXL
> >>   port's driver (portdrv) and the cxl_pci driver. The CXL port device's RAS
> >>   is handled by a notifier callback in the cxl_pci endpoint driver.
> >>
> >>   Most of the patches in this patchset could be reused to work with
> >>   solution#3 or solution#2. The atomic notifier could be dropped and
> >>   instead use an auxiliary device or AER driver awareness. The other
> >>   changes in this patchset could possibly be reused.
> >>
> >>   [1] Kernel.org -
> >>   https://lore.kernel.org/all/f4b23710-059a-51b7-9d27-b62e8b358b54@linux.intel.com
> >>   [2] PCI6.0 - 6.2.10 Internal errors
> >>
> >>  drivers/cxl/core/core.h    |   4 +
> >>  drivers/cxl/core/pci.c     | 153 ++++++++++++++++++++++++++++++++-----
> >>  drivers/cxl/core/port.c    |   6 +-
> >>  drivers/cxl/core/trace.h   |  34 +++++++++
> >>  drivers/cxl/cxl.h          |  10 +++
> >>  drivers/cxl/cxlpci.h       |   2 +
> >>  drivers/cxl/mem.c          |  32 +++++++-
> >>  drivers/cxl/pci.c          |  19 ++++-
> >>  drivers/pci/pcie/aer.c     |  10 ++-
> >>  drivers/pci/pcie/err.c     |  20 +++++
> >>  drivers/pci/pcie/portdrv.c |  32 ++++++++
> >>  drivers/pci/pcie/portdrv.h |   2 +
> >>  include/linux/aer.h        |   6 ++
> >>  13 files changed, 303 insertions(+), 27 deletions(-)
> >>
> >>
> >> base-commit: ca3d4767c8054447ac2a58356080e299a59e05b8
> >> -- 
> >> 2.34.1
> >>