Re: [PATCH v4 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] earlyprintk: missing 'tdx' option in decompression stub parser causes silent loss of early logs
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commit bd0f2326d287e01b5e4cf6ddb08a23b05a98652a
Author: Vishal Verma <vishal.l.verma@intel.com>

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

This commit adds an earlyprintk=tdx option to drive the UART with TDVMCALLs
in a TDX guest. This avoids the #VE exception that would normally be required
to emulate port I/O.

> diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
> --- 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]
Does adding this option here also require an update to the decompression
stub's parser in arch/x86/boot/early_serial_console.c?

The decompression stub uses its own parse_earlyprintk() function to
initialize the UART base address, but it only matches serial, ttyS, and
pciserial. Because it doesn't recognize tdx, early_serial_base remains 0,
and console_init() skips setting up the serial console during
decompression.

Ironically, the older earlyprintk=serial safely avoids #VE in the
decompression stub because early_tdx_detect() overrides pio_ops.f_outb to
use TDVMCALLs. Users migrating to earlyprintk=tdx might unknowingly lose
decompression output.

Should parse_earlyprintk() in the boot code be updated to recognize tdx
as well to avoid losing early logs?

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Sashiko AI review · https://sashiko.dev/#/patchset/20261005-b4-tdx_earlyprintk_tdcalls-v4-0-3f7c56dd568a@intel.com?part=2