Re: [PATCH v5 2/2] x86/early_printk: Add earlyprintk=tdx to drive the UART with TDVMCALLs

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] x86/boot: missing earlyprintk=tdx support in parse_earlyprintk()
--

commit f1945c05c983a94ab54fe2daf5b1ddd281e8d948
Author: Vishal Verma <vishal.l.verma@intel.com>

x86/early_printk: Add earlyprintk=tdx to drive the UART with TDVMCALLs

This patch adds an earlyprintk=tdx option along with tdx_serial_in() and
tdx_serial_out() accessors so that a TDX guest can drive the early serial
console directly with TDVMCALLs rather than triggering #VE exceptions on
port I/O instructions.

> diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
> index cba75306e5b62..04dadcd73b857 100644
> --- a/arch/x86/kernel/early_printk.c
> +++ b/arch/x86/kernel/early_printk.c
[ ... ]
> @@ -414,6 +429,11 @@ static int __init setup_early_printk(char *buf)
>  			early_serial_init(buf + 4);
>  			early_console_register(&early_serial_console, keep);
>  		}
> +		if (!strncmp(buf, "tdx", 3)) {
> +			early_serial_tdx_init();
> +			early_console_register(&early_serial_console, keep);
> +			break;
> +		}

[Severity: Medium]
As reported by Sashiko on v4 [1], when booting with earlyprintk=tdx, this
adds support in setup_early_printk(), but parse_earlyprintk() in the boot
and decompression code only checks for "serial" and "ttyS":

arch/x86/boot/early_serial_console.c:parse_earlyprintk() {
	if (cmdline_find_option("earlyprintk", arg, sizeof(arg)) > 0) {
		char *e;

		if (!strncmp(arg, "serial", 6)) {
			port = DEFAULT_SERIAL_PORT;
			pos += 6;
		}
		...
	}

	if (port)
		early_serial_init(port, baud);
}

In extract_kernel() -> console_init() -> early_serial_console_init() ->
parse_earlyprintk(), early_tdx_detect() has already wired up the port I/O
operations to use TDVMCALLs in a TDX guest. However, because
parse_earlyprintk() does not recognize "tdx", port remains 0 and
early_serial_init() is skipped, leaving early_serial_base unset during
kernel decompression.

Should parse_earlyprintk() in arch/x86/boot/early_serial_console.c also
handle "tdx" so that decompressor serial console output is not lost when
switching from earlyprintk=serial to earlyprintk=tdx?

[1] https://lore.kernel.org/r/20261005-b4-tdx_earlyprintk_tdcalls-v4-2-3f7c56dd568a@intel.com

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261102-b4-tdx_earlyprintk_tdcalls-v5-0-b01bc95d44ff@intel.com?part=2