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Message-ID: <0600959d-9e10-fb1f-b3a9-862a51b9d8e1@intel.com>
Date:   Wed, 7 Jun 2023 09:05:14 -0700
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Subject: Re: [PATCH v11 11/20] x86/virt/tdx: Fill out TDMRs to cover all TDX
 memory regions
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To:     Kai Huang <kai.huang@intel.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     linux-mm@kvack.org, kirill.shutemov@linux.intel.com,
        tony.luck@intel.com, peterz@infradead.org, tglx@linutronix.de,
        seanjc@google.com, pbonzini@redhat.com, david@redhat.com,
        dan.j.williams@intel.com, rafael.j.wysocki@intel.com,
        ying.huang@intel.com, reinette.chatre@intel.com,
        len.brown@intel.com, ak@linux.intel.com, isaku.yamahata@intel.com,
        chao.gao@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com,
        bagasdotme@gmail.com, sagis@google.com, imammedo@redhat.com
References: <cover.1685887183.git.kai.huang@intel.com>
 <927ec9871721d2a50f1aba7d1cf7c3be50e4f49b.1685887183.git.kai.huang@intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <927ec9871721d2a50f1aba7d1cf7c3be50e4f49b.1685887183.git.kai.huang@intel.com>
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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.