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Date:   Tue, 9 Nov 2021 18:15:24 +0100
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Subject: Re: [RFC PATCH v2 24/69] KVM: x86: Introduce "protected guest"
 concept and block disallowed ioctls
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To:     Xiaoyao Li <xiaoyao.li@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>
Cc:     isaku.yamahata@gmail.com,
        "Yamahata, Isaku" <isaku.yamahata@intel.com>, x86@kernel.org,
        Joerg Roedel <joro@8bytes.org>,
        Jim Mattson <jmattson@google.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>, erdemaktas@google.com,
        Connor Kuehl <ckuehl@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
References: <cover.1625186503.git.isaku.yamahata@intel.com>
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 <209a57e9-ca9c-3939-4aaa-4602e3dd7cdd@amd.com>
 <6f0d243c-4f40-d608-3309-5c37536ab866@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <6f0d243c-4f40-d608-3309-5c37536ab866@intel.com>
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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