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X-CSE-ConnectionGUID: LE7MwlaTQ66dyy+Eo2npmQ== X-CSE-MsgGUID: V+hZCCUzRWKaedx4OU55ZA== X-IronPort-AV: E=McAfee;i="6800,10657,11870"; a="112430533" X-IronPort-AV: E=Sophos;i="6.25,215,1779174000"; d="scan'208";a="112430533" Received: from orviesa008.jf.intel.com ([10.64.159.148]) by fmvoesa101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Aug 2026 07:08:06 -0700 X-CSE-ConnectionGUID: j69EllATQs+Kr2sneJB2zw== X-CSE-MsgGUID: Jc8JHvBiTA+BUh1ndSTzTQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,215,1779174000"; d="scan'208";a="262535992" Received: from aschende-mobl.amr.corp.intel.com (HELO [10.125.110.41]) ([10.125.110.41]) by orviesa008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Aug 2026 07:08:06 -0700 Message-ID: <8e40862e-891a-4cad-8bb8-06ad25ad6061@intel.com> Date: Mon, 10 Aug 2026 07:08:04 -0700 Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 10/11] Documentation/x86: Add documentation for TDX's Dynamic PAMT To: Rick Edgecombe , bp@alien8.de, hpa@zytor.com, kas@kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, nik.borisov@suse.com, pbonzini@redhat.com, seanjc@google.com, tglx@kernel.org, vannapurve@google.com, x86@kernel.org, chao.gao@intel.com, yan.y.zhao@intel.com, kai.huang@intel.com, tony.lindgren@linux.intel.com, binbin.wu@intel.com, sohil.mehta@intel.com Cc: Hongyu Ning , Binbin Wu References: <20260806020850.1221381-1-rick.p.edgecombe@intel.com> <20260806020850.1221381-11-rick.p.edgecombe@intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit > +Dynamic PAMT > +------------ > + > +Physical Address Metadata Table (PAMT) is memory that the TDX module needs > +to keep data about each page (think like struct page). It needs to be handed > +to the TDX module for its exclusive use. For normal PAMT, this is installed > +when the TDX module is first loaded and comes to about 0.4% of system memory. The Physical Address Metadata Table (PAMT) is metadata in which the TDX module keeps data about each physical page (think struct page). Space for it is allocated by the VMM, consumes up to about 0.4% of system memory and needs to be supplied to the TDX module for the TDX module is first loaded. Dynamic PAMT is an add-on feature that allows a VMM to dynamically allocate the part of the PAMT which tracks 4k pages. This reduces the amount of memory that TDX consumes while TDs are not in use. Slight tweaks for those first two paragraphs ^ > +When Dynamic PAMT is in use, dmesg shows it like:: > + > + [..] virt/tdx: Enable Dynamic PAMT > + [..] virt/tdx: 10092 KB allocated for PAMT > + [..] virt/tdx: TDX-Module initialized > + > +Dynamic PAMT is only enabled when supported and the ``tdx_dpamt=`` kernel > +parameter is set to "on". The feature is off by default because TDX module > +internal details prevent Dynamic PAMT from working on all keyid partitioning > +configurations. When the TDX module is fixed to include these constraints in > +its enumeration of Dynamic PAMT support, kernel support can be changed to > +default on. For more information, consult the Intel TDX documentation about > +Dynamic PAMT.