linux-kernel - Re: [RFC PATCH 25/35] KVM: x86: Update __get_sregs() / __set

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Message-ID: <20200914213708.GC7192@sjchrist-ice>
Date:   Mon, 14 Sep 2020 14:37:08 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [RFC PATCH 25/35] KVM: x86: Update __get_sregs() / __set_sregs()
 to support SEV-ES

On Mon, Sep 14, 2020 at 03:15:39PM -0500, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> Since many of the registers used by the SEV-ES are encrypted and cannot
> be read or written, adjust the __get_sregs() / __set_sregs() to only get
> or set the registers being tracked (efer, cr0, cr4 and cr8) once the VMSA
> is encrypted.

Is there an actual use case for writing said registers after the VMSA is
encrypted?  Assuming there's a separate "debug mode" and live migration has
special logic, can KVM simply reject the ioctl() if guest state is protected?