Re: [PATCH][v2] x86/bugs: Fix GDS mitigation select for non-ARCH_CAP_GDS_CTRL CPUs

[Pawan Gupta]

On Sat, Aug 16, 2025 at 08:19:05AM +0800, lirongqing wrote:
> From: Li RongQing <lirongqing@xxxxxxxxx>
> 
> The current GDS mitigation logic incorrectly returns early when
> ARCH_CAP_GDS_CTRL is not present, which leads to two problems:

... not present? or the attack vector mitigation is turned off?

> 1. CPUs without ARCH_CAP_GDS_CTRL support are incorrectly marked with
>    GDS_MITIGATION_OFF when they should be marked as
>    GDS_MITIGATION_UCODE_NEEDED.
> 
> 2. The mitigation state checks and locking verification that follow are
>    skipped, which means:
>    - fail to detect if the mitigation was locked
>    - miss the warning when trying to disable a locked mitigation
> 
> Remove the early return to ensure proper mitigation state handling. This
> allows:
> - Proper mitigation classification for non-ARCH_CAP_GDS_CTRL CPUs
> - Complete mitigation state verification
> 
> The change fixes the following runtime issues observed:
> 
> [    2.809147] unchecked MSR access error: WRMSR to 0x123 (tried to write 0x0000000000000010) at rIP: 0xffffffffb34527b8 (update_gds_msr+0x38/0xe0)
> [    2.809147] Call Trace:
> [    2.809147]  <TASK>
> [    2.809147]  identify_secondary_cpu+0x72/0x90
> [    2.809147]  start_secondary+0x7a/0x140
> [    2.809147]  common_startup_64+0x13e/0x141
> [    2.809147]  </TASK>
> [    2.809147] ------------[ cut here ]------------
> [    2.809147] WARNING: CPU: 1 PID: 0 at arch/x86/kernel/cpu/bugs.c:1053 update_gds_msr+0x9b/0xe0
> 
> Fixes: 8c7261abcb7ad ("x86/bugs: Add attack vector controls for GDS")
> Suggested-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
> Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>