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