linux-kernel - RE: [PATCH v11 18/20] x86: Handle TDX erratum to reset TDX private memory during kexec() and reboot

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Date:   Mon, 12 Jun 2023 13:18:01 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'kirill.shutemov@...ux.intel.com'" <kirill.shutemov@...ux.intel.com>,
        "Huang, Kai" <kai.huang@...el.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "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 v11 18/20] x86: Handle TDX erratum to reset TDX private
 memory during kexec() and reboot

From: kirill.shutemov@...ux.intel.com
> Sent: 12 June 2023 12:49
> 
> On Mon, Jun 12, 2023 at 10:27:44AM +0000, Huang, Kai wrote:
> > Does it make sense?
> 
> I understand your logic. AFAICS, it is correct (smp_mb() instead of __mb()
> would be better), but it is not justified from complexity PoV.

Given that x86 performs writes pretty much in code order.
Do you need anything more than a compile barrier?

> This lockless exercise gave me a pause to understand.
> 
> Lockless doesn't buy you anything here, only increases complexity.
> Just take a lock.

Indeed...

	David

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