linux-kernel - Re: [PATCH v7 09/20] x86/virt/tdx: Get information about TDX module and TDX-capable memory

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Date:   Fri, 2 Dec 2022 21:57:37 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "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>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "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>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "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 09/20] x86/virt/tdx: Get information about TDX module
 and TDX-capable memory

On Fri, 2022-12-02 at 09:25 -0800, Dave Hansen wrote:
> On 12/2/22 03:19, Huang, Kai wrote:
> > Probably I forgot to mention the "r9" in practice always returns 32, so there
> > will be empty CMRs at the tail of the cmr_array[].
> 
> Right, so the r9 value is basically useless.  I bet the code gets
> simpler if you just ignore it.
> 
> > > But we can also do nothing here, but just skip empty CMRs when comparing the
> > > memory region to it (in next patch).
> > > 
> > > Or, we don't even need to explicitly check memory region against CMRs. If the
> > > memory regions that we provided in the TDMR doesn't fall into CMR, then
> > > TDH.SYS.CONFIG will fail. We can just depend on the SEAMCALL to do that.
> > 
> > Sorry to ping, but do you have any comments here?
> > 
> > How about we just don't do any check of TDX memory regions against CMRs, but
> > just let the TDH.SYS.CONFIG SEAMCALL to determine?
> 
> Right, if we screw it up TDH.SYS.CONFIG SEAMCALL will fail.  We don't
> need to add more code to detect that failure ourselves.  TDX is screwed
> either way.

Will do.  Thanks.