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From:   Lai Jiangshan <jiangshanlai@gmail.com>
Date:   Tue, 30 Nov 2021 19:18:32 +0800
Message-ID: <CAJhGHyA4EEiW37iwrZ7EXOTXC7aQHvGLaK_RSrMc++u1bepj5g@mail.gmail.com>
Subject: Re: [RFC PATCH v3 53/59] KVM: x86: Add a helper function to restore 4
 host MSRs on exit to user space
To:     Chao Gao <chao.gao@intel.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>, isaku.yamahata@intel.com,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Erdem Aktas <erdemaktas@google.com>,
        Connor Kuehl <ckuehl@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        LKML <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org,
        isaku.yamahata@gmail.com
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On Tue, Nov 30, 2021 at 4:10 PM Chao Gao <chao.gao@intel.com> wrote:

>
> No, it is already documented in public spec.

In intel-tdx-module-1.5-base-spec-348549001.pdf, page 79
"recoverability hist",  I think it is a "hint".

>
> TDX module spec just says some MSRs are reset to INIT state by TDX module
> (un)conditionally during TD exit. When to restore these MSRs to host's
> values is decided by host.
>


Sigh, it is quite a common solution to reset a register to a default
value here, for example in VMX, the host GDT.limit and host TSS.limit
is reset after VMEXIT, so load_fixmap_gdt() and invalidate_tss_limit()
have to be called in host in vmx_vcpu_put().

Off-topic: Is it a good idea to also put load_fixmap_gdt() and
invalidate_tss_limit() in user-return-notfier?