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Date:   Tue, 13 Jun 2023 17:24:54 -0700
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Subject: Re: [PATCH v11 18/20] x86: Handle TDX erratum to reset TDX private
 memory during kexec() and reboot
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To:     "Huang, Kai" <kai.huang@intel.com>,
        "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>
Cc:     "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "Luck, Tony" <tony.luck@intel.com>,
        "david@redhat.com" <david@redhat.com>,
        "bagasdotme@gmail.com" <bagasdotme@gmail.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Chatre, Reinette" <reinette.chatre@intel.com>,
        "Christopherson,, Sean" <seanjc@google.com>,
        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "Yamahata, Isaku" <isaku.yamahata@intel.com>,
        "Shahar, Sagi" <sagis@google.com>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "imammedo@redhat.com" <imammedo@redhat.com>,
        "Gao, Chao" <chao.gao@intel.com>,
        "Brown, Len" <len.brown@intel.com>,
        "sathyanarayanan.kuppuswamy@linux.intel.com" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "Huang, Ying" <ying.huang@intel.com>,
        "Williams, Dan J" <dan.j.williams@intel.com>
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 <1542a26c0501cb9f7fc330d8aa27e565c81b969c.camel@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <1542a26c0501cb9f7fc330d8aa27e565c81b969c.camel@intel.com>
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On 6/13/23 16:18, Huang, Kai wrote:
> On Tue, 2023-06-13 at 07:25 -0700, Hansen, Dave wrote:
>> On 6/12/23 17:51, Huang, Kai wrote:
>>> If we introduce a helper to mark a page as TDX private page,
>> Let me get this right: you have working, functional code for a
>> highly-unlikely scenario (kernel bugs or even more rare hardware
>> errors).  But, you want to optimize this super-rare case?  It's not fast
>> enough?
>>
>> Is there any other motivation here that I'm missing?
>>
> No it's not about speed.  The motivation is to have a common code to yield less
> line of code, though I don't have clear number of how many LoC can be reduced.

OK, so ... ballpark.  How many lines of code are we going to _save_ for
this super-rare case?  10?  100?  1000?

The upside is saving X lines of code ... somewhere.  The downside is
adding Y lines of code ... somewhere else and maybe breaking things in
the process.

You've evidently done _some_ kind of calculus in your head to make this
tradeoff worthwhile.  I'd love to hear what your calculus is, even if
it's just a gut feel.

Could you share your logic here, please?