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Date: Thu, 21 May 2026 21:51:27 +0200
From: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
To: "Bowman, Terry" <terry.bowman@amd.com>
Cc: "Dan Williams (nvidia)" <djbw@kernel.org>, Mauro Carvalho Chehab
 <mchehab@kernel.org>, Dave Jiang <dave.jiang@intel.com>, Smita Koralahalli
 <smita.koralahallichannabasappa@amd.com>, Robert Richter
 <rrichter@amd.com>, Jonathan Cameron <jic23@kernel.org>, Shiju Jose
 <shiju.jose@huawei.com>, Sathyanarayanan Kuppuswamy
 <sathyanarayanan.kuppuswamy@linux.intel.com>, "linux-cxl@vger.kernel.org"
 <linux-cxl@vger.kernel.org>, Ben Cheatham <Benjamin.Cheatham@amd.com>,
 Lukas Wunner <lukas@wunner.de>, "PradeepVineshReddy.Kodamati@amd.com"
 <PradeepVineshReddy.Kodamati@amd.com>, "linux-kernel@vger.kernel.org"
 <linux-kernel@vger.kernel.org>
Subject: Re: RFC: CXL: How to handle trace event ABI break from
 CXL_HEADERLOG_SIZE fix?
Message-ID: <20260521215127.327549ff@foz.lan>
In-Reply-To: <7c9cb682-ec3e-438b-830c-2a5997b69c43@amd.com>
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On Thu, 21 May 2026 07:23:45 -0500
"Bowman, Terry" <terry.bowman@amd.com> wrote:

> On 5/20/2026 5:18 PM, Dan Williams (nvidia) wrote:
> > Bowman, Terry wrote:  
> >> Hi Mauro and Everyone,
> >>
> >> During development of the CXL protocol series [1], the Sashiko tool 
> >> identified an issue in the CXL RAS UCE trace logging for Ports and Endpoints. 
> >> Specifically, the CXL RAS UCE header log size is incorrectly defined in 
> >> drivers/cxl/cxl.h.
> >>
> >> The UCE header log size is currently defined as 128 u32s (512 bytes),
> >> whereas it should be 16 u32s (64 bytes) per CXL r4.0 8.2.4.17.7. Correcting 
> >> this will change the trace format and break the existing ABI contract 
> >> with rasdaemon.
> >>
> >> How would you recommend proceeding to resolve this?  
> > 
> > Split the definitions into one that reads from the register space and
> > once that passes the parsed log to the trace buffer.
> > 
> > Something like:
> > 
> > u32 hl[CXL_HEADERLOG_TRACE_SIZE_U32];
> > 
> > ...zero-fill that and put a comment about how userspace has already
> > grown a dependency on the buggy size.
> > 
> > In other words, keep the userspace compatibility, but fix the iomem
> > overflow.  
> 
> Ok, that's straight forward. Thanks.

Such approach sounds good to me.

Regards,
Mauro

Thanks,
Mauro