linux-kernel - Re: [PATCH 1/2] x86/numa: Introduce numa_fill

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Message-ID: <ZGbCG4gRGow0VCmQ@aschofie-mobl2>
Date:   Thu, 18 May 2023 17:26:03 -0700
From:   Alison Schofield <alison.schofield@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Dave Jiang <dave.jiang@...el.com>, x86@...nel.org,
        linux-cxl@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/numa: Introduce numa_fill_memblks()

On Thu, May 18, 2023 at 05:08:16PM -0700, Dave Hansen wrote:
> On 5/18/23 17:04, alison.schofield@...el.com wrote:
> > The initial use case is the ACPI driver that needs to extend
> > SRAT defined proximity domains to an entire CXL CFMWS Window[1].
> 
> Dumb question time: Why didn't the SRAT just cover this sucker in the
> first place?  Are we fixing up a BIOS bug or is there a legitimate
> reason that the SRAT didn't cover it up front?
> 
>

There is no requirement that the BIOS describe (in the SRAT) all the
HPA assigned to a CFMWS Window. The HPA range may not actually map to
any memory at boot time. It can be persistent capacity or may be there
to enable hot-plug. IIUC BIOS can pick and choose and define volatile
regions wherever it pleases.

So, no we're not fixing up a BIOS bug, nor doing a BIOS sanity check.