Re: [PATCH v2 0/1] cxl/pmem: debug invalid serial number data

[Jonathan Cameron]

On Fri, 14 Feb 2025 11:09:51 +0800
Yuquan Wang <wangyuquan1236@xxxxxxxxxxxxxx> wrote:

> Background
> ==========
> In Qemu environment, the default serial number of cxl-type3 device
> is UI64_NULL.

Doesn't matter but technically it's just not presented by QEMU unless
specified.

The internal default is UI64_NULL but if we match that when creating
the config space stuff we just skip the serial number capability.

I'm glad to see some hardening around this as I ran into same thing
long ago (that's when I realized we were missing serial number support :(

Jonathan

> But we could still use it to create a nvdimm pmem region
> and set a non-zero cookie of nd_interleave_set, for example:
>   1. create a cxl pmem region interleaved with 2 devices (one with
>      serial number 0 and the other with serial number 1), and the cookie
>      would be non-zero/valid.
>   2. create the second cxl pmem region by 1 device with no serial number
>      and this region would have a non-zero cookie because the offset of
>      dpa is non-zero.
> 
> Problem
> =======
> In a nvdimm interleave-set each device with an invalid or zero
> serial number may cause pmem region initialization to fail, but in
> cxl case such device could still set cookies of nd_interleave_set
> and create a nvdimm pmem region.
> 
> CXL Pmem Validation
> ===================
> This patch adds the validation of serial number in cxl pmem region creation.
> The event of no serial number would cause to fail to set the cookie
> and pmem region.
> 
> cxl-test
> ========
> A mock serial number is set from the platform device id and 0 is a valid
> platform device id. For cxl-test to work properly, always +1 on mock
> device's serial number.
> 
> Yuquan Wang (1):
>   cxl/pmem: debug invalid serial number data
> 
>  drivers/cxl/pmem.c           | 7 +++++++
>  tools/testing/cxl/test/mem.c | 2 +-
>  2 files changed, 8 insertions(+), 1 deletion(-)
>