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

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Message-ID: <20230614110821.pf35kxd4vcwjjpb5@box>
Date:   Wed, 14 Jun 2023 14:08:21 +0300
From:   "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To:     "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

On Wed, Jun 14, 2023 at 10:58:13AM +0000, Huang, Kai wrote:
> > And the platform has to
> > handle erratum in BIOS to reset memory status on reboot anyway.
> 
> So "handle erratum in BIOS" I think you mean "warm reset" doesn't reset TDX
> private pages, and the BIOS needs to disable "warm reset".
> 
> IIUC this means the kernel needs to depend on specific BIOS setting to work
> normally, and IIUC the kernel even cannot be aware of this setting?
> 
> Should the kernel just reset all TDX private pages when erratum is present
> during reboot so the kernel doesn't depend on BIOS?

Kernel cannot really function if we don't trust BIOS to do its job. Kernel
depends on BIOS services anyway. We cannot try to handle everything in
kernel just in case BIOS drops the ball.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov