Re: [PATCH v4 3/3] PCI/AER: Clear UNCOR_STATUS bits that might be ANFE

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu,  9 May 2024 16:48:33 +0800
Zhenzhong Duan <zhenzhong.duan@intel.com> wrote:

> When processing an ANFE, ideally both correctable error(CE) status and
> uncorrectable error(UE) status should be cleared. However, there is no
> way to fully identify the UE associated with ANFE. Even worse, Non-Fatal
> Error(NFE) may set the same UE status bit as ANFE. Treating an ANFE as
> NFE will bring some issues, i.e., breaking softwore probing; treating
> NFE as ANFE will make us ignoring some UEs which need active recover
> operation. To avoid clearing UEs that are not ANFE by accident, the
> most conservative route is taken here: If any of the NFE Detected bits
> is set in Device Status, do not touch UE status, they should be cleared
> later by the UE handler. Otherwise, a specific set of UEs that may be
> raised as ANFE according to the PCIe specification will be cleared if
> their corresponding severity is Non-Fatal.
> 
> For instance, previously when kernel receives an ANFE with Poisoned TLP
> in OS native AER mode, only status of CE will be reported and cleared:
> 
>   AER: Correctable error message received from 0000:b7:02.0
>   PCIe Bus Error: severity=Correctable, type=Transaction Layer, (Receiver ID)
>     device [8086:0db0] error status/mask=00002000/00000000
>      [13] NonFatalErr
> 
> If the kernel receives a Malformed TLP after that, two UEs will be
> reported, which is unexpected. Malformed TLP Header is lost since
> the previous ANFE gated the TLP header logs:
> 
>   PCIe Bus Error: severity="Uncorrectable (Fatal), type=Transaction Layer, (Receiver ID)
>     device [8086:0db0] error status/mask=00041000/00180020
>      [12] TLP                    (First)
>      [18] MalfTLP
> 
> Now, for the same scenario, both CE status and related UE status will be
> reported and cleared after ANFE:
> 
>   AER: Correctable error message received from 0000:b7:02.0
>   PCIe Bus Error: severity=Correctable, type=Transaction Layer, (Receiver ID)
>     device [8086:0db0] error status/mask=00002000/00000000
>      [13] NonFatalErr
>     Uncorrectable errors that may cause Advisory Non-Fatal:
>      [18] TLP
> 
> Tested-by: Yudong Wang <yudong.wang@intel.com>
> Co-developed-by: "Wang, Qingshun" <qingshun.wang@linux.intel.com>
> Signed-off-by: "Wang, Qingshun" <qingshun.wang@linux.intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

This is nasty enough though that it would benefit from more review
if possible.  

Thanks for all the detailed explanations in the patch descriptions,
that made it less painful than it might have been.

Jonathan