linux-kernel - Re: [RFC PATCH v5 027/104] KVM: TDX: initialize VM with TDX specific parameters

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Date:   Thu, 07 Apr 2022 13:51:38 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>, isaku.yamahata@...el.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
        erdemaktas@...gle.com, Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 027/104] KVM: TDX: initialize VM with TDX
 specific parameters

On Thu, 2022-04-07 at 09:29 +0800, Xiaoyao Li wrote:
> On 4/5/2022 8:58 PM, Paolo Bonzini wrote:
> > On 3/4/22 20:48, isaku.yamahata@...el.com wrote:
> > > +    td_params->attributes = init_vm->attributes;
> > > +    if (td_params->attributes & TDX_TD_ATTRIBUTE_PERFMON) {
> > > +        pr_warn("TD doesn't support perfmon. KVM needs to save/restore "
> > > +            "host perf registers properly.\n");
> > > +        return -EOPNOTSUPP;
> > > +    }
> > 
> > Why does KVM have to hardcode this (and LBR/AMX below)?  Is the level of 
> > hardware support available from tdx_caps, for example through the CPUID 
> > configs (0xA for this one, 0xD for LBR and AMX)?
> 
> It's wrong code. PMU is allowed.
> 
> AMX and LBR are disallowed because and the time we wrote the codes they 
> are not supported by KVM. Now AMX should be allowed, but (arch-)LBR 
> should be still blocked until KVM merges arch-LBR support.

I think Isaku's idea is we don't support them in the first submission?

If so as I suggested, we should add a TODO in comment..