linux-kernel - Re: [PATCH v10 05/16] x86/virt/tdx: Add skeleton to enable TDX on demand

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Message-ID: <20230314171603.GE3922605@ls.amr.corp.intel.com>
Date:   Tue, 14 Mar 2023 10:16:03 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Isaku Yamahata <isaku.yamahata@...il.com>,
        "Huang, Kai" <kai.huang@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "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>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "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>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Luck, Tony" <tony.luck@...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 v10 05/16] x86/virt/tdx: Add skeleton to enable TDX on
 demand

On Mon, Mar 13, 2023 at 10:45:45PM -0700,
Dave Hansen <dave.hansen@...el.com> wrote:

> On 3/13/23 21:02, Isaku Yamahata wrote:
> >> Then it is a hidden behaviour of the TDX module that is not reflected in the
> >> spec.  I am not sure whether we should handle because: 
> >>
> >> 1) This is an extremely rare case.  Kernel would be basically under attack if
> >> such error happened.  In the current series we don't handle such case in
> >> KEY.CONFIG either but just leave a comment (see patch 13).
> >>
> >> 2) Not sure whether this will be changed in the future.
> >>
> >> So I think we should keep as is.
> > TDX 1.5 spec introduced TDX_RND_NO_ENTROPY status code.  For TDX 1.0, let's
> > postpone it to TDX 1.5 activity.
> 
> What the heck does this mean?
> 
> I don't remember seeing any code here that checks for "TDX 1.0" or "TDX
> 1.5".  That means that this code needs to work with _any_ TDX version.
> 
> Are features being added to new versions that break code written for old
> versions?

No new feature, but new error code. TDX_RND_NO_ENTROPY, lack of entropy.
For TDX 1.0, some APIs return TDX_SYS_BUSY. It can be contention(lock failure)
or the lack of entropy.  The caller can't distinguish them.
For TDX 1.5, they return TDX_RND_NO_ENTROPY instead of TDX_SYS_BUSY in the case
of rdrand/rdseed failure.

Because both TDX_SYS_BUSY and TDX_RND_NO_ENTROPY are recoverable error
(bit 63 error=1, bit 62 non_recoverable=0), the caller can check error bit and
non_recoverable bit for retry.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>