[PATCH] riscv: errata: select RISCV_ALTERNATIVE_EARLY for THEAD GHOSTWRITE

[Paul Walmsley]

On Thu, 17 Sep 2026, Zongmin Zhou wrote:

> From: Zongmin Zhou <zhouzongmin at kylinos.cn>
> 
> errata_probe_ghostwrite() only marks the CPU as vulnerable when it is
> called at the RISCV_ALTERNATIVES_EARLY_BOOT stage, and the mitigation
> in ghostwrite_enable_mitigation() only takes effect if the vulnerable
> state was recorded before the boot alternatives are patched.
> 
> The early boot stage is only executed when CONFIG_RISCV_ALTERNATIVE_EARLY
> is enabled, which currently is only selected by ERRATA_THEAD_MAE. In a
> kernel built with ERRATA_THEAD_GHOSTWRITE=y but ERRATA_THEAD_MAE=n, the
> early alternatives never run, so ghostwrite_state is never set to
> VULNERABLE: ghostwrite_enable_mitigation() returns false, xtheadvector
> remains enabled, and sysfs reports "Not affected" on a vulnerable
> T-Head C9xx CPU.
> 
> Select RISCV_ALTERNATIVE_EARLY from ERRATA_THEAD_GHOSTWRITE so that the
> vulnerability is detected in the early boot stage and the default
> mitigation is applied.
> 
> Fixes: 4bf97069239b ("riscv: Add ghostwrite vulnerability")
> Signed-off-by: Zongmin Zhou <zhouzongmin at kylinos.cn>

Thanks, queued for v7.3-rc.


- Paul