linux-kernel - Re: [PATCH v3 12/21] x86/virt/tdx: Create TDMRs to cover all system RAM

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Message-ID: <a651a489-ecc5-2439-61b1-03ff43cff7f6@intel.com>
Date:   Fri, 29 Apr 2022 06:52:21 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, len.brown@...el.com,
        tony.luck@...el.com, rafael.j.wysocki@...el.com,
        reinette.chatre@...el.com, dan.j.williams@...el.com,
        peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        isaku.yamahata@...el.com
Subject: Re: [PATCH v3 12/21] x86/virt/tdx: Create TDMRs to cover all system
 RAM

On 4/29/22 00:24, Kai Huang wrote:
> On Thu, 2022-04-28 at 09:22 -0700, Dave Hansen wrote:
>> On 4/5/22 21:49, Kai Huang wrote:
>>> implies that one TDMR could cover multiple e820 RAM entries.  If a RAM
>>> entry spans the 1GB boundary and the former part is already covered by
>>> the previous TDMR, just create a new TDMR for the latter part.
>>>
>>> TDX only supports a limited number of TDMRs (currently 64).  Abort the
>>> TDMR construction process when the number of TDMRs exceeds this
>>> limitation.
>>
>> ... and what does this *MEAN*?  Is TDX disabled?  Does it throw away the
>> RAM?  Does it eat puppies?
> 
> How about:
> 
> 	TDX only supports a limited number of TDMRs.  Simply return error when
> 	the number of TDMRs exceeds the limitation.  TDX is disabled in this
> 	case.

Better, but two things there that need to be improved.  This is a cover
letter.  Talking at the function level ("return error") is too
low-level.  It's also slipping into passive mode "is disabled".  Fixing
those, it looks like this:

	TDX only supports a limited number of TDMRs.  Disable TDX if all
	TDMRs are consumed but there is more RAM to cover.