linux-kernel - Re: [RFC PATCH v2 24/69] KVM: x86: Introduce "protected guest" concept and block disallowed ioctls

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Message-ID: <3966eaf0-ed8e-c356-97dd-f8c5c3057439@redhat.com>
Date:   Tue, 9 Nov 2021 18:15:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     isaku.yamahata@...il.com,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>, x86@...nel.org,
        Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [RFC PATCH v2 24/69] KVM: x86: Introduce "protected guest"
 concept and block disallowed ioctls

On 11/9/21 14:37, Xiaoyao Li wrote:
> 
> Tom,
> 
> I think what you did in this commit is not so correct. It just silently 
> ignores the ioctls insteaf of returning an error to userspace to tell 
> this IOCTL is not invalid to this VM. E.g., for 
> kvm_arch_vcpu_ioctl_get_fpu(), QEMU just gets it succesful with fpu 
> being all zeros.

Yes, it's a "cop out" that removes the need for more complex changes in 
QEMU.

I think for the get/set registers ioctls 
KVM_GET/SET_{REGS,SREGS,FPU,XSAVE,XCRS} we need to consider SEV-ES 
backwards compatibility.  This means, at least for now, only apply the 
restriction to TDX (using a bool-returning function, see the review for 
28/69).

For SMM, MCE, vCPU events and for kvm_valid/dirty_regs, it can be done 
as in this patch.

Paolo