From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.20]) (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 6888A3090C2 for ; Mon, 13 Jul 2026 16:01:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.20 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783958508; cv=none; b=Kye4q5POAVMMsm21iM6qeQkb6hUgNVbfswSiv+dkGLtybheTwYJfg0yLAst2XNWU861FngeJDo/GtuV6T057bQXpOqHN0yH76fjFRUmHuWR1KVrAK/0qfVb5NXOeHThZ+w4GRIy6/TuCRw8S7mcuS4i5KdORb1HzQ2/7BKCpYEE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783958508; c=relaxed/simple; bh=CD954zLyW+H+N700cDO8caRM/+OWbiqnsi8A3hbhkKg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=l3UJ6vUgOrFo+uByvJg7O2UQZouwuVAuShIlML1aiqQ/vY/CZRJhT9pUJ3mi/KNNxPaY9LtBLuBkb8d0j2jyDCzBqesA046q/hdDQ3hTPEFXR8zpjgE6XzlYQ8neGhrU+hZ7GNnU4xy1W1o3/IEbZEcxE0FPtujsHba7lB9fsEQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com; spf=pass smtp.mailfrom=linux.intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=NJsNTqsz; arc=none smtp.client-ip=198.175.65.20 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="NJsNTqsz" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1783958506; x=1815494506; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=CD954zLyW+H+N700cDO8caRM/+OWbiqnsi8A3hbhkKg=; b=NJsNTqszoFL2lIEnjT3uA220H6AoBiyyafyjqatbT03l7daIJAEzIK54 /CJtV0+zF0QOgLsNs6RQV1doaSRveH3TJbcYbOoh0xYh3BZ8kijLNyZD7 qQSbMXJJWtUlTF06vUasnLu7g033Cb+HZgPtA0k+hv/IsubWpjzC7cKYT 1vmMSPNUJs82wCnSyL7oBWGlRp+WtP8skm/xeJiM73Cwey+3F7Q6oadZ5 E1gmJpf6dD9ofSAJTtjxZsC4+05C7k7DugUBzTPQfMM/Suizxs7jTLYq7 ycDaEDCeCmAUzScI2rFAI6boRyaFNFLyrmQAh7oNftUhnyeQuILNESkfA w==; X-CSE-ConnectionGUID: 0D+VjRLBS2uSwZnzwGQWtQ== X-CSE-MsgGUID: 5dAUIcYaQsSQCRydDxbgPA== X-IronPort-AV: E=McAfee;i="6800,10657,11841"; a="84348800" X-IronPort-AV: E=Sophos;i="6.25,154,1779174000"; d="scan'208";a="84348800" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by orvoesa112.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Jul 2026 09:01:45 -0700 X-CSE-ConnectionGUID: CPAh3dhWSUGNs6dbqkEkbQ== X-CSE-MsgGUID: 21ZP3ox8SRypvlTcge7k1w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,154,1779174000"; d="scan'208";a="249238465" Received: from unknown (HELO [10.24.80.90]) ([10.24.80.90]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Jul 2026 09:01:45 -0700 Message-ID: <680a2be7-5a10-448d-8552-cb9ef64b6be7@linux.intel.com> Date: Mon, 13 Jul 2026 09:01:38 -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 1/2] x86/tdx: Add helper to query maximum TD Quote size To: Peter Fang , Dave Hansen , Kiryl Shutsemau , Rick Edgecombe Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org References: <20260612110853.3188196-1-peter.fang@intel.com> <20260612110853.3188196-2-peter.fang@intel.com> Content-Language: en-US From: Kuppuswamy Sathyanarayanan In-Reply-To: <20260612110853.3188196-2-peter.fang@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/12/2026 4:08 AM, Peter Fang wrote: > TDX attestation blob ("TD Quote") sizes can grow with newer > cryptographic schemes, so guests can no longer rely on a fixed-size > buffer for the Quote. > > Newer TDX modules report the maximum TD Quote size via a TD-scope > metadata field. Add a helper to query it instead of exposing tdg_vm_rd() > directly, as it can read arbitrary metadata fields. > > Thanks to Xu Yilun for suggesting this. I'm not sure what the original suggestion was. Perhaps a link to the discussion (or Xu Yilun's email) would be helpful for context. > > Assisted-by: Claude:claude-opus-4-7 > Assisted-by: GitHub Copilot:gpt-5.4 > Signed-off-by: Peter Fang > --- Looks good to me. Reviewed-by: Kuppuswamy Sathyanarayanan > arch/x86/coco/tdx/tdx.c | 19 +++++++++++++++++++ > arch/x86/include/asm/shared/tdx.h | 1 + > arch/x86/include/asm/tdx.h | 2 ++ > 3 files changed, 22 insertions(+) > > diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c > index 186915a17c50..88c66c46e70a 100644 > --- a/arch/x86/coco/tdx/tdx.c > +++ b/arch/x86/coco/tdx/tdx.c > @@ -197,6 +197,25 @@ u64 tdx_hcall_get_quote(u8 *buf, size_t size) > } > EXPORT_SYMBOL_GPL(tdx_hcall_get_quote); > > +/** > + * tdx_get_max_quote_size() - Get the maximum TD Quote size > + * > + * Read the maximum size of a TD Quote from a 4-byte TD metadata field. The TDX > + * guest driver uses it to size the buffer for Quote retrieval. Older TDX > + * modules do not support this field and return an error. > + * > + * Return: Maximum Quote size in bytes on success, or 0 on failure. > + */ > +u32 tdx_get_max_quote_size(void) > +{ > + u64 val, ret; > + > + ret = tdg_vm_rd(TDCS_QUOTE_MAX_SIZE, &val); > + > + return ret ? 0 : (u32)val; > +} > +EXPORT_SYMBOL_GPL(tdx_get_max_quote_size); > + > static void __noreturn tdx_panic(const char *msg) > { > struct tdx_module_args args = { > diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h > index 049638e3da74..2880f493a8e5 100644 > --- a/arch/x86/include/asm/shared/tdx.h > +++ b/arch/x86/include/asm/shared/tdx.h > @@ -49,6 +49,7 @@ > /* TDX TD-Scope Metadata. To be used by TDG.VM.WR and TDG.VM.RD */ > #define TDCS_CONFIG_FLAGS 0x1110000300000016 > #define TDCS_TD_CTLS 0x1110000300000017 > +#define TDCS_QUOTE_MAX_SIZE 0x9010000200000008 > #define TDCS_NOTIFY_ENABLES 0x9100000000000010 > #define TDCS_TOPOLOGY_ENUM_CONFIGURED 0x9100000000000019 > > diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h > index a149740b24e8..ac39674c9479 100644 > --- a/arch/x86/include/asm/tdx.h > +++ b/arch/x86/include/asm/tdx.h > @@ -72,6 +72,8 @@ int tdx_mcall_extend_rtmr(u8 index, u8 *data); > > u64 tdx_hcall_get_quote(u8 *buf, size_t size); > > +u32 tdx_get_max_quote_size(void); > + > void __init tdx_dump_attributes(u64 td_attr); > void __init tdx_dump_td_ctls(u64 td_ctls); > -- Sathyanarayanan Kuppuswamy Linux Kernel Developer