linux-kernel - Re: [PATCH v11 11/20] x86/virt/tdx: Fill out TDMRs to cover all TDX memory regions

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Message-ID: <0600959d-9e10-fb1f-b3a9-862a51b9d8e1@intel.com>
Date:   Wed, 7 Jun 2023 09:05:14 -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:     linux-mm@...ck.org, kirill.shutemov@...ux.intel.com,
        tony.luck@...el.com, peterz@...radead.org, tglx@...utronix.de,
        seanjc@...gle.com, pbonzini@...hat.com, david@...hat.com,
        dan.j.williams@...el.com, rafael.j.wysocki@...el.com,
        ying.huang@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, ak@...ux.intel.com, isaku.yamahata@...el.com,
        chao.gao@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v11 11/20] x86/virt/tdx: Fill out TDMRs to cover all TDX
 memory regions

On 6/4/23 07:27, Kai Huang wrote:
> +	/*
> +	 * Loop over TDX memory regions and fill out TDMRs to cover them.
> +	 * To keep it simple, always try to use one TDMR to cover one
> +	 * memory region.
> +	 *
> +	 * In practice TDX1.0 supports 64 TDMRs, which is big enough to
> +	 * cover all memory regions in reality if the admin doesn't use
> +	 * 'memmap' to create a bunch of discrete memory regions.  When
> +	 * there's a real problem, enhancement can be done to merge TDMRs
> +	 * to reduce the final number of TDMRs.
> +	 */

Rather than focus in on one specific command-line parameter, let's just say:

	In practice TDX supports at least 64 TDMRs.  A 2-socket system
	typically only consumes <NUMBER> of those.  This code is dumb
	and simple and may use more TMDRs than is strictly required.

Let's also put a pr_warn() in here if we exceed, say 1/2 or maybe 3/4 of
the 64.  We'll hopefully start to get reports somewhat in advance if
systems get close to the limit.