linux-kernel - Re: [PATCH v7 13/20] x86/virt/tdx: Allocate and set up PAMTs for TDMRs

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Message-ID: <2b370efc0bc7803bd5aaacde30fd80ce59606646.camel@intel.com>
Date:   Mon, 28 Nov 2022 23:14:56 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "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>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.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>,
        "Shahar, Sagi" <sagis@...gle.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 v7 13/20] x86/virt/tdx: Allocate and set up PAMTs for
 TDMRs

On Mon, 2022-11-28 at 14:56 -0800, Hansen, Dave wrote:
> On 11/28/22 14:48, Huang, Kai wrote:
> > > Maybe even a little ASCII diagram about the different tmb configurations
> > > that this can find:
> > > 
> > > > TDMR1 | TDMR2 |
> > >    |---tmb---|
> > >           |tmb|
> > >           |------tmb-------|          <- case 3)
> > >    |------tmb-------|                 <- case 4
> > Thanks for the diagram!
> > 
> > But IIUC it seems the above case 3) and 4) are actually not possible, since when
> > one TDMR is created, it's end is always rounded up to the end of TMB it tries to
> > cover (the rounded-up end may cover the entire or only partial of other TMBs,
> > though).
> 
> OK, but at the same time, we shouldn't *STRICTLY* specialize every
> single little chunk of this code to be aware of every other tiny little
> implementation detail.
> 
> Let's say tomorrow's code has lots of TDMRs left, but fills up one
> TDMR's reserved areas and has to "split" it.  Want to bet on whether the
> person that adds that patch will be able to find this code and fix it up?

Yeah good point.

> 
> Or, say that the TDMR creation algorithm changes and they're not done in
> order of ascending physical address.
> 
> This code actually gets easier and more obvious if you ignore the other
> details.

Agreed.  Thanks.