From nobody Thu Sep 24 17:56:19 2026 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (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 815AF3ADB8D; Mon, 21 Sep 2026 19:53:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790020384; cv=none; b=C6IlpikXoA43plhh8c31OLBywE4yVDJhkrqVwjs10wOCQdDitOk5SmWfc3Rk+KeoOK3cdv82l5GCZ+7Ea+HTM2nnnJ325nhmFdyyyrjlULcGI0exQw1ZzR2Zw78jsJJZ12N5Cc1bHT+N3VV4HYEBjfxW4BKmTG3+JSU/ufl6Kdc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790020384; c=relaxed/simple; bh=yYFOxPWxF+ebjxNifaNu6ojjenfBN450qHPMmQOo3ao=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=q5R3pg+QkVH95hOHQccdAx0Io4I5SGXOzMYfF7AMnN8dzhrdw0ruGc7kJsrRduYtgxKlylcPQZJLySJD08XRczmYGBzEP9S2l7kG/SqemgWL/gbsx+fNv8AjSW6fD12jqh3I9uMFKqqd39Vy4hKIfUAN8nK6PVgFIQBFC5JkSDM= 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=CsOEqiJI; arc=none smtp.client-ip=192.198.163.17 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="CsOEqiJI" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1790020381; x=1821556381; h=from:date:subject:mime-version:content-transfer-encoding: message-id:references:in-reply-to:to:cc; bh=yYFOxPWxF+ebjxNifaNu6ojjenfBN450qHPMmQOo3ao=; b=CsOEqiJIb57nJKXg5eh3yrZAyUzLbrt6p7fwhtUQAuquN4au8UdcXN43 k7F+GcmuAtLQFIShW/xQm4PcZZevv5vrGqTpNfCYeRzMyG2sM/oPZE1NI OGMkTVr4+dCUfsOGe6xHMHKSB8QVIX153Mc4fn4e8SHusksuvcTOTVRSo QwXSxD6OxrHkr9MehR7XGPN0MARy++0hLHWTVsoQJlTOpbHZuNePvF6GC ZF1SIvJtDY4GBL5Ql0r9wb1GlS2wqnsnSm3J4EwRt6IHNxb1Wr5qn09qg SVp+ponHcZ2jdJma32YWCX1KJ23ebDV9BBD2Qg5dxZkhRJac5bgW+gDLL w==; X-CSE-ConnectionGUID: ofBG8jPDRWiovVFe2GxQ9A== X-CSE-MsgGUID: DH1QyfS9TNmkQr7F2eYdnw== X-IronPort-AV: E=McAfee;i="6800,10657,11912"; a="90435107" X-IronPort-AV: E=Sophos;i="6.27,115,1787036400"; d="scan'208";a="90435107" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2026 12:53:01 -0700 X-CSE-ConnectionGUID: SNK0lIiUTJC40e0k5wZXSg== X-CSE-MsgGUID: +Ss2GkCrT+6FKUIuHE16TA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,115,1787036400"; d="scan'208";a="299041228" Received: from vverma7-desk1.amr.corp.intel.com (HELO [192.168.1.200]) ([10.125.109.250]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2026 12:53:00 -0700 From: Vishal Verma Date: Mon, 21 Sep 2026 13:52:37 -0600 Subject: [PATCH v2 1/2] x86/tdx: Move port I/O definitions to a shared header Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260921-b4-tdx_earlyprintk_tdcalls-v2-1-ad1fde3f25fd@intel.com> References: <20260921-b4-tdx_earlyprintk_tdcalls-v2-0-ad1fde3f25fd@intel.com> In-Reply-To: <20260921-b4-tdx_earlyprintk_tdcalls-v2-0-ad1fde3f25fd@intel.com> To: x86@kernel.org, Dave Hansen , Kiryl Shutsemau , Rick Edgecombe , Jonathan Corbet , Shuah Khan , Randy Dunlap Cc: linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, linux-doc@vger.kernel.org, Vishal Verma X-Mailer: b4 0.16-dev-62088 X-Developer-Signature: v=1; a=openpgp-sha256; l=3102; i=vishal.l.verma@intel.com; h=from:subject:message-id; bh=yYFOxPWxF+ebjxNifaNu6ojjenfBN450qHPMmQOo3ao=; b=owGbwMvMwCXGf25diOft7jLG02pJDFkbu6X7sp6GHLFns5x3/6TAl/vH75yrOftWXOOcy3mBn adeM6sIdZSyMIhxMciKKbL83fOR8Zjc9nyewARHmDmsTCBDGLg4BWAiVzYx/NOO1tl70uOudsCL 3pXT/OSsBKz6nK7f+t3S1lFk2Hyi8S3DP/39Oxa+UFieFHF+T81d7rXnWkLyGV/rT//YxX//9av QDEYA X-Developer-Key: i=vishal.l.verma@intel.com; a=openpgp; fpr=F8682BE134C67A12332A2ED07AFA61BEA3B84DFF In preparation for adding a 'tdx' option for early_printk which uses direct TDVMCALLs for I/O, factor out the PORT_READ and PORT_WRITE definitions from arch/x86/coco/tdx/tdx.c into arch/x86/include/asm/shared/tdx.h, and namespace them with 'TDVMCALL_'. The decompressor also used 0/1 literals in its tdx_io_{in,out} helpers - switch those to use the new definitions. Signed-off-by: Vishal Verma Reviewed-by: Kiryl Shutsemau (Meta) Cc: Rick Edgecombe --- arch/x86/include/asm/shared/tdx.h | 6 ++++++ arch/x86/boot/compressed/tdx.c | 4 ++-- arch/x86/coco/tdx/tdx.c | 8 ++------ 3 files changed, 10 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/share= d/tdx.h index f20e91d7ac35..ecaf965f059b 100644 --- a/arch/x86/include/asm/shared/tdx.h +++ b/arch/x86/include/asm/shared/tdx.h @@ -84,6 +84,12 @@ #define TDVMCALL_STATUS_ALIGN_ERROR 0x8000000000000002ULL #define TDVMCALL_STATUS_SUBFUNC_UNSUPPORTED 0x8000000000000003ULL =20 +/* + * TDG.VP.VMCALL direction (passed in R13) + */ +#define TDVMCALL_PORT_READ 0 +#define TDVMCALL_PORT_WRITE 1 + /* * Bitmasks of exposed registers (with VMM). */ diff --git a/arch/x86/boot/compressed/tdx.c b/arch/x86/boot/compressed/tdx.c index 8451d6a1030c..ed278bac3c93 100644 --- a/arch/x86/boot/compressed/tdx.c +++ b/arch/x86/boot/compressed/tdx.c @@ -22,7 +22,7 @@ static inline unsigned int tdx_io_in(int size, u16 port) .r10 =3D TDX_HYPERCALL_STANDARD, .r11 =3D hcall_func(EXIT_REASON_IO_INSTRUCTION), .r12 =3D size, - .r13 =3D 0, + .r13 =3D TDVMCALL_PORT_READ, .r14 =3D port, }; =20 @@ -38,7 +38,7 @@ static inline void tdx_io_out(int size, u16 port, u32 val= ue) .r10 =3D TDX_HYPERCALL_STANDARD, .r11 =3D hcall_func(EXIT_REASON_IO_INSTRUCTION), .r12 =3D size, - .r13 =3D 1, + .r13 =3D TDVMCALL_PORT_WRITE, .r14 =3D port, .r15 =3D value, }; diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c index f904a636d449..7d1a93ee2534 100644 --- a/arch/x86/coco/tdx/tdx.c +++ b/arch/x86/coco/tdx/tdx.c @@ -24,10 +24,6 @@ #define EPT_READ 0 #define EPT_WRITE 1 =20 -/* Port I/O direction */ -#define PORT_READ 0 -#define PORT_WRITE 1 - /* See Exit Qualification for I/O Instructions in VMX documentation */ #define VE_IS_IO_IN(e) ((e) & BIT(3)) #define VE_GET_IO_SIZE(e) (((e) & GENMASK(2, 0)) + 1) @@ -691,7 +687,7 @@ static bool handle_in(struct pt_regs *regs, int size, i= nt port) .r10 =3D TDX_HYPERCALL_STANDARD, .r11 =3D hcall_func(EXIT_REASON_IO_INSTRUCTION), .r12 =3D size, - .r13 =3D PORT_READ, + .r13 =3D TDVMCALL_PORT_READ, .r14 =3D port, }; bool success; @@ -720,7 +716,7 @@ static bool handle_out(struct pt_regs *regs, int size, = int port) * "TDG.VP.VMCALL". */ return !_tdx_hypercall(hcall_func(EXIT_REASON_IO_INSTRUCTION), size, - PORT_WRITE, port, regs->ax & mask); + TDVMCALL_PORT_WRITE, port, regs->ax & mask); } =20 /* --=20 2.55.0 From nobody Thu Sep 24 17:56:19 2026 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (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 B03FF3B38B4; Mon, 21 Sep 2026 19:53:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790020385; cv=none; b=O0HemlAy4tFlp/38MD2zYfpY89oT6ZMqO3Tn30WSuaoFzD6HIWBWpyhjU531n5Zia7aIdJBsq1j7s2DHLPH8OCXGad5gQ8aceP1JcYYENw9JGTfVqv1Ylpsg0n0yyvMzaGBKBSOiAXryzFCuqSaP6iyCsvlxg6Q3F5w7XtWFQ7M= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790020385; c=relaxed/simple; bh=W498o8WnVx17/urOz4pvsvYQLkUTwiQaaBOsNKX2Gt8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=jBHpZ4+7DIpf+HIbgrw6dXhfa8BGI1deKk0/qMYiptP2Y154EzfSl+tv+XJod507p64epj0dGlIqHXU2L2KiOfgxAI16G4HN08puCZCAiKO8aarb4GUnkXzpkx58fOpeRzrHNr+Q89n5cIXSW5gCQakB0K8xaaOColJzwnQQpXQ= ARC-Authentication-Results: i=1; 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X-CSE-ConnectionGUID: 7UFw56sjRKS6Rhgdlk6vaA== X-CSE-MsgGUID: NVVnCYvxQ4KLPLZdL3+IOg== X-IronPort-AV: E=McAfee;i="6800,10657,11912"; a="90435115" X-IronPort-AV: E=Sophos;i="6.27,115,1787036400"; d="scan'208";a="90435115" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2026 12:53:02 -0700 X-CSE-ConnectionGUID: Lg7RJ1CDTKmANU0f8YVZ3g== X-CSE-MsgGUID: cOjnP5h2TEqkL5DKzrOExQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,115,1787036400"; d="scan'208";a="299041231" Received: from vverma7-desk1.amr.corp.intel.com (HELO [192.168.1.200]) ([10.125.109.250]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2026 12:53:01 -0700 From: Vishal Verma Date: Mon, 21 Sep 2026 13:52:38 -0600 Subject: [PATCH v2 2/2] x86/early_printk: Add earlyprintk=tdx to drive the UART with TDVMCALLs Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260921-b4-tdx_earlyprintk_tdcalls-v2-2-ad1fde3f25fd@intel.com> References: <20260921-b4-tdx_earlyprintk_tdcalls-v2-0-ad1fde3f25fd@intel.com> In-Reply-To: <20260921-b4-tdx_earlyprintk_tdcalls-v2-0-ad1fde3f25fd@intel.com> To: x86@kernel.org, Dave Hansen , Kiryl Shutsemau , Rick Edgecombe , Jonathan Corbet , Shuah Khan , Randy Dunlap Cc: linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, linux-doc@vger.kernel.org, Vishal Verma X-Mailer: b4 0.16-dev-62088 X-Developer-Signature: v=1; a=openpgp-sha256; l=6861; i=vishal.l.verma@intel.com; h=from:subject:message-id; bh=W498o8WnVx17/urOz4pvsvYQLkUTwiQaaBOsNKX2Gt8=; b=owGbwMvMwCXGf25diOft7jLG02pJDFkbu6V7HXeo/Y83ixEXXitcxJP0VfV9n0rHbs4a6Qm2L NM5jH07SlkYxLgYZMUUWf7u+ch4TG57Pk9ggiPMHFYmkCEMXJwCMBHpQ4wM1/ra2+YkrJ9ZmHTh wMnd34svNW/7bHG/pTAp6tKVC4c3hzAyTN/0iHf+nz1PMyO3hh4vESq7zPt6acy8RM6WR091Ug5 /YgAA X-Developer-Key: i=vishal.l.verma@intel.com; a=openpgp; fpr=F8682BE134C67A12332A2ED07AFA61BEA3B84DFF A TDX guest cannot execute port I/O instructions directly, but earlyprintk's serial console still issues plain inb()/outb() and lets each one fault into the #VE handler to be emulated as a TDVMCALL. While that works, it is a roundabout way to get a character out. early_serial_putc() polls the LSR, and then writes a byte, but since the TDX guest can't directly do port I/O, a #VE exception is raised. The #VE handler must call TDG.VP.VEINFO.GET to find out what faulted, and then it can issue the TDVMCALL that does the actual work. This makes #VE a functional mechanism for doing I/O, which is not desirable, is unnecessarily complicated and fragile, and results in twice the number of calls into the TDX module. Instead, add an earlyprintk=3Dtdx option, which can issue the TDVMCALLs directly. Add a pair of tdx_serial_in() and tdx_serial_out() accessors and set them up in this case. Note that the output does not appear any earlier - "earlyprintk=3D" is an early_param(), so the console is still registered from parse_early_param(). This only changes how the bytes leave the guest once it is up. LLMs were used under supervision to create this patch, to help understand the scope and mechanisms, create testing instrumentation (throwaway) to count #VEs in the serial vs tdx earlyprintk setups, and to drive lab machines to do this testing. Signed-off-by: Vishal Verma --- Documentation/admin-guide/kernel-parameters.txt | 9 ++++++ arch/x86/include/asm/tdx.h | 3 ++ arch/x86/coco/tdx/tdx.c | 39 +++++++++++++++++++++= ++++ arch/x86/kernel/early_printk.c | 37 +++++++++++++++++++++= ++ 4 files changed, 88 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/admin-guide/kernel-parameters.txt index 33cd30996e47..263a806afd2a 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1543,6 +1543,7 @@ Kernel parameters earlyprintk=3Dserial[,ttySn[,baudrate]] earlyprintk=3Dserial[,0x...[,baudrate]] earlyprintk=3DttySn[,baudrate] + earlyprintk=3Dtdx[,ttySn[,baudrate]] earlyprintk=3Ddbgp[debugController#] earlyprintk=3Dmmio32,membase[,{nocfg|baudrate}] earlyprintk=3Dpciserial[,force],bus:device.function[,{nocfg|baudrate}] @@ -1556,6 +1557,14 @@ Kernel parameters Use "nocfg" to skip UART configuration, assume BIOS/firmware has configured UART correctly. =20 + On x86, "tdx" is equivalent to "serial", except that + in a TDX guest the serial port is driven with + TDVMCALLs rather than port I/O instructions, avoiding + the #VE exception that would otherwise be taken to + emulate every access. Outside a TDX guest it falls + back to port I/O and behaves exactly like "serial". + If CONFIG_INTEL_TDX_GUEST is not set, it is ignored. + Append ",keep" to not disable it when the real console takes over. =20 diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h index 89e97d5761d8..325dd7c5929f 100644 --- a/arch/x86/include/asm/tdx.h +++ b/arch/x86/include/asm/tdx.h @@ -83,6 +83,9 @@ int tdx_mcall_extend_rtmr(u8 index, u8 *data); =20 u64 tdx_hcall_get_quote(u8 *buf, size_t size); =20 +u8 tdx_inb(u16 port); +void tdx_outb(u8 value, u16 port); + void __init tdx_dump_attributes(u64 td_attr); void __init tdx_dump_td_ctls(u64 td_ctls); =20 diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c index 7d1a93ee2534..4377fcca2c99 100644 --- a/arch/x86/coco/tdx/tdx.c +++ b/arch/x86/coco/tdx/tdx.c @@ -194,6 +194,45 @@ u64 tdx_hcall_get_quote(u8 *buf, size_t size) } EXPORT_SYMBOL_GPL(tdx_hcall_get_quote); =20 +/** + * tdx_inb() - Read a byte from an I/O port without a #VE + * @port: I/O port to read from + * + * Ask the VMM to perform the read with TDG.VP.VMCALL, rat= her + * than executing an IN instruction and having the resulting #VE emulate i= t. + * + * Return: the byte read, or 0xff if the hypercall failed. + */ +u8 tdx_inb(u16 port) +{ + struct tdx_module_args args =3D { + .r10 =3D TDX_HYPERCALL_STANDARD, + .r11 =3D hcall_func(EXIT_REASON_IO_INSTRUCTION), + .r12 =3D 1, + .r13 =3D TDVMCALL_PORT_READ, + .r14 =3D port, + }; + + if (__tdx_hypercall(&args)) + return 0xff; + + return args.r11; +} + +/** + * tdx_outb() - Write a byte to an I/O port without a #VE + * @value: byte to write + * @port: I/O port to write to + * + * Ask the VMM to perform the write with TDG.VP.VMCALL, ra= ther + * than executing an OUT instruction and having the resulting #VE emulate = it. + */ +void tdx_outb(u8 value, u16 port) +{ + _tdx_hypercall(hcall_func(EXIT_REASON_IO_INSTRUCTION), 1, + TDVMCALL_PORT_WRITE, port, value); +} + static void __noreturn tdx_panic(const char *msg) { struct tdx_module_args args =3D { diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c index cba75306e5b6..2721e48783cd 100644 --- a/arch/x86/kernel/early_printk.c +++ b/arch/x86/kernel/early_printk.c @@ -21,6 +21,7 @@ #include #include #include +#include =20 /* Simple VGA output */ #define VGABASE (__ISA_IO_base + 0xb8000) @@ -111,6 +112,32 @@ ANNOTATE_NOENDBR_SYM(io_serial_out); DEFINE_STATIC_CALL(serial_in, io_serial_in); DEFINE_STATIC_CALL(serial_out, io_serial_out); =20 +#ifdef CONFIG_INTEL_TDX_GUEST +/* + * A TDX guest cannot execute port I/O instructions, so ask the VMM to do = it. + */ +static __noendbr unsigned int tdx_serial_in(unsigned long addr, int offset) +{ + return tdx_inb(addr + offset); +} +ANNOTATE_NOENDBR_SYM(tdx_serial_in); + +static __noendbr void tdx_serial_out(unsigned long addr, int offset, int v= alue) +{ + tdx_outb(value, addr + offset); +} +ANNOTATE_NOENDBR_SYM(tdx_serial_out); + +static __init void early_serial_tdx_init(void) +{ + if (!cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) + return; + + static_call_update(serial_in, tdx_serial_in); + static_call_update(serial_out, tdx_serial_out); +} +#endif /* CONFIG_INTEL_TDX_GUEST */ + static int early_serial_putc(unsigned char ch) { unsigned timeout =3D 0xffff; @@ -414,6 +441,16 @@ static int __init setup_early_printk(char *buf) early_serial_init(buf + 4); early_console_register(&early_serial_console, keep); } +#ifdef CONFIG_INTEL_TDX_GUEST + if (!strncmp(buf, "tdx", 3)) { + buf +=3D 3; + early_serial_tdx_init(); + early_serial_init(buf); + early_console_register(&early_serial_console, keep); + if (!strncmp(buf, ",ttyS", 5)) + buf +=3D 5; + } +#endif #ifdef CONFIG_PCI if (!strncmp(buf, "pciserial", 9)) { buf +=3D 9; /* Keep from match the above "pciserial" */ --=20 2.55.0