linux-kernel - Re: [PATCH V2 1/8] perf/x86/uncore: Save the unit control address of all units

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Message-ID: <20240617155027.GX8774@noisy.programming.kicks-ass.net>
Date: Mon, 17 Jun 2024 17:50:27 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: kan.liang@...ux.intel.com
Cc: mingo@...nel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
	namhyung@...nel.org, irogers@...gle.com, eranian@...gle.com,
	ak@...ux.intel.com, yunying.sun@...el.com,
	tim.c.chen@...ux.intel.com
Subject: Re: [PATCH V2 1/8] perf/x86/uncore: Save the unit control address of
 all units

On Fri, Jun 14, 2024 at 06:46:24AM -0700, kan.liang@...ux.intel.com wrote:
> From: Kan Liang <kan.liang@...ux.intel.com>
> 
> The unit control address of some CXL units may be wrongly calculated
> under some configuration on a EMR machine.
> 
> The current implementation only saves the unit control address of the
> units from the first die, and the first unit of the rest of dies. Perf
> assumed that the units from the other dies have the same offset as the
> first die. So the unit control address of the rest of the units can be
> calculated. However, the assumption is wrong, especially for the CXL
> units.

Oh gawd, that's terrible. Was this actually specified, or are we hacking
around a firmware fail?