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

[Li,Rongqing]

> -----Original Message-----
> From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
> Sent: 2025年8月19日 1:33
> To: Li,Rongqing <lirongqing@xxxxxxxxx>
> Cc: tglx@xxxxxxxxxxxxx; bp@xxxxxxxxx; peterz@xxxxxxxxxxxxx;
> jpoimboe@xxxxxxxxxx; mingo@xxxxxxxxxx; dave.hansen@xxxxxxxxxxxxxxx;
> x86@xxxxxxxxxx; hpa@xxxxxxxxx; david.kaplan@xxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Subject: [????] Re: [PATCH][v2] x86/bugs: Fix GDS mitigation select for
> non-ARCH_CAP_GDS_CTRL CPUs
> 
> 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?


Should be "When the attack vector mitigation is turned off"

I will send v3, thanks

-Li

> 
> > 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>