linux-kernel - Re: [PATCH v8 11/16] x86/virt/tdx: Designate reserved areas for all TDMRs

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Message-ID: <778a6c80-a955-620d-a82a-c2ca82f26363@intel.com>
Date:   Mon, 9 Jan 2023 17:22:08 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Huang, Kai" <kai.huang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "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>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "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 v8 11/16] x86/virt/tdx: Designate reserved areas for all
 TDMRs

On 1/9/23 17:19, Huang, Kai wrote:
>> It's probably also worth noting *somewhere* that there's a balance to be
>> had between TDMRs and reserved areas.  A system that is running out of
>> reserved areas in a TDMR could split a TDMR to get more reserved areas.
>> A system that has run out of TDMRs could relatively easily coalesce two
>> adjacent TDMRs (before the PAMTs are allocated) and use a reserved area
>> if there was a gap between them.
> We can add above to the changelog of this patch, or the patch 09 ("x86/virt/tdx:
> Fill out TDMRs to cover all TDX memory regions").  The latter perhaps is better
> since that patch is the first place where the balance of TDMRs and reserved
> areas is related.
> 
> What is your suggestion?

Just put it close to the code that actually hits the problem so the
potential solution is close at hand to whoever hits the problem.