linux-kernel - Re: [PATCH v3 07/13] KVM: selftests: x86: Fix the checks to XFD

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Message-ID: <ZB4LAzgNsbKdTESk@google.com>
Date:   Fri, 24 Mar 2023 13:41:39 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Mingwei Zhang <mizhang@...gle.com>, g@...gle.com
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>,
        Venkatesh Srinivas <venkateshs@...gle.com>,
        Aaron Lewis <aaronlewis@...gle.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Chao Gao <chao.gao@...el.com>
Subject: Re: [PATCH v3 07/13] KVM: selftests: x86: Fix the checks to XFD_ERR
 using and operation

On Tue, Feb 21, 2023, Mingwei Zhang wrote:
> Fix the checks to XFD_ERR using logical AND operation because XFD_ERR might
> contain more information in the future. According Intel SDM Vol 1. 13.14:

If that happens, then the future change is responsible for updating the check.
The test very clearly does a straight write of MSR_IA32_XFD.  If there are extra
bits set then something is broken.

	wrmsr(MSR_IA32_XFD, XFEATURE_MASK_XTILEDATA);