linux-kernel - Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of error

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Date:   Wed, 23 Nov 2022 17:37:33 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Huang, Kai" <kai.huang@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of
 error

On Wed, Nov 23, 2022, Dave Hansen wrote:
> On 11/23/22 08:20, Sean Christopherson wrote:
> >>> Why is it done that way?
> >>>
> >>> Can it be changed to delay TDX initialization until the first TDX guest
> >>> needs to run?
> >>>
> >> Sean suggested.
> >>
> >> Hi Sean, could you commenet?
> > Waiting until the first TDX guest is created would result in false advertising,
> > as KVM wouldn't know whether or not TDX is actually supported until that first
> > VM is created.  If we can guarantee that TDH.SYS.INIT will fail if and only if
> > there is a kernel bug, then I would be ok deferring the "enabling" until the
> > first VM is created.
> 
> There's no way we can guarantee _that_.  For one, the PAMT* allocations
> can always fail.  I guess we could ask sysadmins to fire up a guest to
> "prime" things, but that seems a little silly.  Maybe that would work as
> the initial implementation that we merge, but I suspect our users will
> demand more determinism, maybe a boot or module parameter.

Oh, you mean all of TDX initialization?  I thought "initialization" here mean just
doing tdx_enable().

Yeah, that's not going to be a viable option.  Aside from lacking determinisim,
it would be all too easy to end up on a system with fragmented memory that can't
allocate the PAMTs post-boot.