linux-kernel - Re: [PATCH v2 2/8] x86/mtrr: support setting MTRR state for software defined MTRRs

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Message-ID: <Y+tP7fvvSFSSCznH@zn.tnic>
Date:   Tue, 14 Feb 2023 10:10:05 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Juergen Gross <jgross@...e.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        lists@...dbynature.de, mikelley@...rosoft.com,
        torvalds@...ux-foundation.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2 2/8] x86/mtrr: support setting MTRR state for software
 defined MTRRs

On Tue, Feb 14, 2023 at 10:02:51AM +0100, Juergen Gross wrote:
> I just don't like the idea of trying to catch all possible misuses in
> lower levels, at the same time introducing the need to modify those
> tests in case a new valid use case is popping up.

So what would you do: generally allow this so that potentially other
guest configurations misuse it?

And when we decide to change it, all those users will come running and
complaining that we broke it?

And then we're stuck with a nasty workaround in the tree because we have
to support them too?

See, all we do here is because of such misguided (or maybe didn't know
better) decisions which have happened a long time ago.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette