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

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Date:   Mon, 13 Feb 2023 16:18:48 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
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 13.02.23 16:11, Borislav Petkov wrote:
> On Mon, Feb 13, 2023 at 04:03:07PM +0100, Borislav Petkov wrote:
>>> Wouldn't !cpu_feature_enabled(X86_FEATURE_HYPERVISOR) be enough?
>>>
>>> I'm not sure we won't need that for TDX guests, too.
>>
>> See, that's the problem. I wanna have it simple too. Lemme check with
>> dhansen.
> 
> He says MTRRs are enabled in TDX guests: "X86_FEATURE_MTRR is fixed to
> 1 in TDX guests."
> 
> So we will have to do the more finer-grained check I guess.

Isn't the check for !X86_FEATURE_MTRR && X86_FEATURE_HYPERVISOR enough
then?

Yes, you still could construct cases where it would go wrong, but I don't
think we should over-engineer it.


Juergen


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