From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F348226158B; Sat, 18 Jul 2026 01:45:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784339129; cv=none; b=RD3W+6BbNiFc3RIiVT9EkfeEPM2BiSljUQCx3zSJG/r+W/N2CAPfHGUsDqouU85Lk0iOPZgwdSV5i6188dGGj9HJMm57xkN9//wnMLqKx1ibRHPPxc4VzY9O+Dz2DZBDlIEmLxo6t+AALDfwFBM08JtUF56GqzvPL1SenvL/+yc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784339129; c=relaxed/simple; bh=nn84tB7jb4o5ROXYXo2hi61apKafyqMBLrSLmPKEziY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=inr/eHYwD1nIDbC0QgTJw9JwrPiushp5vEgvQf35ydGtn2FhOmqjmoJtoj1ImZmZDIWAGlGxj5EQVvePpwcTp+kzXRGvVHXn0DtEICb1hlgiGKDoslErOJNV6XhSaz8J947kw93w1eIzXgzll1bfj0eUyuGJjzHIFUjWYnf76rA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=dct5vA4+; arc=none smtp.client-ip=192.198.163.10 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="dct5vA4+" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1784339127; x=1815875127; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=nn84tB7jb4o5ROXYXo2hi61apKafyqMBLrSLmPKEziY=; b=dct5vA4+u0SMdXS0Sf3ou+G2PRE+uivK3uk2QUoFIAEXplF8O1JakA0+ msk96i0zpgx8k12SPRkGfClvRORK6+QQbEfMYvkss/IOB27+TWMROA13X W5steKnIWNtdoQftuvE568vLh1/1TqJp3LRoT9+BK3jXII7nCvQF5xAeP BiCRt4SW95tO108jTSYvEJAVWwFapezUmsdA73PW/i6JzbJSD9r5KPnue XQwglSwHi8h25LvGZZ6N24A47ObX+bJgYV7rzAs9IDA73uGVE2Nvzip4v cTPoeS8SK8aMOHDgqZmnUCPrsXAZncWud8lMidBkToaWhDV+TNLRomGL0 Q==; X-CSE-ConnectionGUID: aFUuBDhmSTeyUCRbGJtqfg== X-CSE-MsgGUID: 1jH+bh91SjOMpU8rjJfVcQ== X-IronPort-AV: E=McAfee;i="6800,10657,11849"; a="96377173" X-IronPort-AV: E=Sophos;i="6.25,170,1779174000"; d="scan'208";a="96377173" Received: from fmviesa008.fm.intel.com ([10.60.135.148]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jul 2026 18:45:17 -0700 X-CSE-ConnectionGUID: ixcNeQuFQFWUEBYqbOz/VQ== X-CSE-MsgGUID: keLndSSYTOeiMTLPlw5s1A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,170,1779174000"; d="scan'208";a="254296285" Received: from rpedgeco-desk.jf.intel.com ([10.88.27.135]) by fmviesa008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jul 2026 18:45:10 -0700 From: Rick Edgecombe To: bp@alien8.de, dave.hansen@intel.com, 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 Cc: rick.p.edgecombe@intel.com Subject: [PATCH v7 09/11] x86/virt/tdx: Enable Dynamic PAMT Date: Fri, 17 Jul 2026 18:44:58 -0700 Message-ID: <20260718014500.2231262-10-rick.p.edgecombe@intel.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260718014500.2231262-1-rick.p.edgecombe@intel.com> References: <20260718014500.2231262-1-rick.p.edgecombe@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Kirill A. Shutemov" The Physical Address Metadata Table (PAMT) holds TDX metadata for physical memory and must be allocated by the kernel during TDX module initialization. Dynamic PAMT is a TDX module feature that can reduce this memory use by allocating part of the PAMT dynamically. The TDX module exposes whether Dynamic PAMT is supported via a bit in the 'features0' metadata. Unfortunately, the TDX module exposes the feature as supported even when it does not support using it with the number of keyids currently configured in the BIOS. Since no TDX modules exist today with that issue fixed, make the feature default off to prevent users from upgrading their kernel and encountering TDX erroring out when trying to enable Dynamic PAMT. For the decision of whether to make it a boot time option and/or compile time option, consider that Dynamic PAMT's memory savings are significant enough to make it a good default configuration. That is most TDX users should want it unless they have strange keyid configurations. The feature increases the kernel size by 2KB (when TDX is configured in the build). All pieces are in place to enable Dynamic PAMT if it is supported and the user passes a kernel parameter. Signed-off-by: Kirill A. Shutemov Co-developed-by: Rick Edgecombe Signed-off-by: Rick Edgecombe Reviewed-by: Tony Lindgren --- v7: - Add kernel parameter following some twists and turns, derriving originally from a comment by (Chao) v6: - After Nikolai pointed out that the TDX docs actually have the Dynamic PAMT pages-per-2MB region fixed at 2 instead of variable sized, I checked over the docs more closely looking for anything else that might have been missed. Spotted this 48 bit physical address bit check in the docs, so added it. --- .../admin-guide/kernel-parameters.txt | 7 +++++++ arch/x86/include/asm/tdx.h | 1 + arch/x86/virt/vmx/tdx/tdx.c | 21 +++++++++++++++++-- 3 files changed, 27 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index b5493a7f8f228..be4928489b02f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1321,6 +1321,13 @@ Kernel parameters The filter can be disabled or changed to another driver later using sysfs. + tdx_dpamt= + [X86] Controls whether TDX will use Dynamic PAMT + to save memory, when supported. + + Valid parameters: "on", "off" + Default: "off" + reg_file_data_sampling= [X86] Controls mitigation for Register File Data Sampling (RFDS) vulnerability. RFDS is a CPU diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h index 9cbd250bbd39b..7910901a7ba21 100644 --- a/arch/x86/include/asm/tdx.h +++ b/arch/x86/include/asm/tdx.h @@ -36,6 +36,7 @@ /* Bit definitions of TDX_FEATURES0 metadata field */ #define TDX_FEATURES0_TD_PRESERVING BIT_ULL(1) #define TDX_FEATURES0_NO_RBP_MOD BIT_ULL(18) +#define TDX_FEATURES0_DYNAMIC_PAMT BIT_ULL(36) #ifndef __ASSEMBLER__ diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c index 61f48fff69df6..f397ea17248e3 100644 --- a/arch/x86/virt/vmx/tdx/tdx.c +++ b/arch/x86/virt/vmx/tdx/tdx.c @@ -47,6 +47,8 @@ #include "seamcall_internal.h" #include "tdx.h" +bool tdx_enable_dpamt __ro_after_init; + struct tdx_module_state { bool initialized; bool sysinit_done; @@ -1028,6 +1030,8 @@ static __init int construct_tdmrs(struct list_head *tmb_list, return ret; } +#define TDX_SYS_CONFIG_DYNAMIC_PAMT BIT(16) + static __init int config_tdx_module(struct tdmr_info_list *tdmr_list, u64 global_keyid) { @@ -1056,6 +1060,12 @@ static __init int config_tdx_module(struct tdmr_info_list *tdmr_list, args.rcx = __pa(tdmr_pa_array); args.rdx = tdmr_list->nr_consumed_tdmrs; args.r8 = global_keyid; + + if (tdx_supports_dynamic_pamt(&tdx_sysinfo)) { + pr_info("Enable Dynamic PAMT\n"); + args.r8 |= TDX_SYS_CONFIG_DYNAMIC_PAMT; + } + ret = seamcall_prerr(TDH_SYS_CONFIG, &args); /* Free the array as it is not required anymore. */ @@ -2041,8 +2051,8 @@ EXPORT_SYMBOL_FOR_KVM(tdh_phymem_page_wbinvd_hkid); bool tdx_supports_dynamic_pamt(const struct tdx_sys_info *sysinfo) { - /* To be enabled when kernel is ready. */ - return false; + return sysinfo->features.tdx_features0 & TDX_FEATURES0_DYNAMIC_PAMT && + tdx_enable_dpamt; } EXPORT_SYMBOL_FOR_KVM(tdx_supports_dynamic_pamt); @@ -2300,6 +2310,13 @@ void tdx_free_control_page(struct page *page) } EXPORT_SYMBOL_FOR_KVM(tdx_free_control_page); +static int __init tdx_dpamt_setup(char *str) +{ + return kstrtobool(str, &tdx_enable_dpamt) == 0; +} + +__setup("tdx_dpamt=", tdx_dpamt_setup); + void tdx_sys_disable(void) { struct tdx_module_args args = {}; -- 2.54.0