Re: [PATCH] PCI: vmd: Enable interrupt ordering quirk for Arrow Lake

[Bjorn Helgaas <helgaas@kernel.org>]

On Fri, Sep 11, 2026 at 12:05:39AM +0400, Vladimir Nedoshivin wrote:
> Intel Arrow Lake VMD device 0xad0b is affected by ARL004. The VMD may
> signal an MSI before preceding posted writes from the child device have
> reached memory, which can cause the demuxed handler to observe stale
> completion data.
> 
> The existing VMD_FEAT_INTERRUPT_QUIRK implements Intel's documented
> workaround by issuing a configuration-space read to the MSI initiator
> before dispatching the interrupt.
> 
> Enable the existing quirk for 0xad0b as well as 0x7d0b and make the
> comments describe both MTL016 and ARL004.
> 
> Tested on an MSI Vector 17 HX AI with Intel VMD 8086:ad0b and an NVMe
> device behind VMD. With the quirk enabled, the NVMe completion stalls
> observed without the workaround are no longer reproduced.
> 
> Link: https://bugs.launchpad.net/bugs/2166325
> Signed-off-by: Vladimir Nedoshivin <gvozd188@mail.ru>

Applied on pci/controller/vmd, thanks!

I added the erratum source and text to the commit logs of both the
Meteor Lake quirk and this one:

  PCI: vmd: Flush DMA writes before handling MSI on Arrow Lake

  Per the Intel Core Ultra Processors (Series 2) Specification Update
  (ID 834774 of 9/1/2026), the Arrow Lake VMD device 0xad0b is affected by an
  MSI erratum:

    ARL004: MSI from VMD-Owned Device May Pass Memory Write

    Problem      When the storage subsystem is configured to operate in RAID
		 0 or 1 mode, a Message Signaled Interrupt (MSI) from an
		 Intel® Volume Management Device (Intel® VMD) owned device
		 may interrupt a core before a previous write from the device
		 is completed.

    Workaround   None identified. The VMD MSI interrupt-handler should
		 initially perform a dummy register read to the MSI initiator
		 device prior to any writes to ensure proper PCIe ordering.

  ...

> ---
>  drivers/pci/controller/vmd.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index e45ef8cb16e..9d97a832785 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -94,7 +94,8 @@ enum vmd_features {
>  	VMD_FEAT_USE_BIOS_INFO		= (1 << 6),
>  
>  	/*
> -	 * Meteor Lake VMD (device ID 0x7d0b) is affected by erratum MTL016:
> +	 * Some Intel VMD devices are affected by interrupt ordering errata,
> +	 * including MTL016 (0x7d0b) and ARL004 (0xad0b):
>  	 * the VMD may signal its MSI before the posted writes that carry the
>  	 * child device's DMA data have landed in memory.  The demuxed handler
>  	 * then runs against a not-yet-coherent completion queue and misses the
> @@ -131,7 +132,7 @@ static DEFINE_RAW_SPINLOCK(list_lock);
>   * @enabled:	true if driver enabled IRQ
>   * @virq:	the virtual IRQ value provided to the requesting driver.
>   * @flush_addr:	config space address of the initiating device, read before
> - *		demuxing to flush its posted writes (MTL016); NULL if the
> + *		demuxing to flush its posted writes; NULL if the
>   *		VMD is not affected.
>   *
>   * Every MSI/MSI-X IRQ requested for a device in a VMD domain will be mapped to
> @@ -1300,7 +1301,7 @@ static const struct pci_device_id vmd_ids[] = {
>  	{PCI_VDEVICE(INTEL, 0x7d0b),
>  		.driver_data = VMD_FEATS_CLIENT | VMD_FEAT_INTERRUPT_QUIRK,},
>  	{PCI_VDEVICE(INTEL, 0xad0b),
> -		.driver_data = VMD_FEATS_CLIENT,},
> +		.driver_data = VMD_FEATS_CLIENT | VMD_FEAT_INTERRUPT_QUIRK,},
>  	{PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_VMD_9A0B),
>  		.driver_data = VMD_FEATS_CLIENT,},
>  	{PCI_VDEVICE(INTEL, 0xb60b),
> 
> base-commit: 95ac22dd4bf13373f90bb6d51bcd1fd1d8f5db54
> -- 
> 2.53.0
>