linux-kernel - RE: [????] Re: [PATCH][v2] x86/bugs: Fix GDS mitigation select for non-ARCH_CAP_GDS

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Message-ID: <455a7ad388c84d95887a5cede25f2825@baidu.com>
Date: Tue, 19 Aug 2025 02:03:07 +0000
From: "Li,Rongqing" <lirongqing@...du.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, "bp@...en8.de" <bp@...en8.de>,
	"peterz@...radead.org" <peterz@...radead.org>, "jpoimboe@...nel.org"
	<jpoimboe@...nel.org>, "mingo@...hat.com" <mingo@...hat.com>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "x86@...nel.org"
	<x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>, "david.kaplan@....com"
	<david.kaplan@....com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [????] Re: [PATCH][v2] x86/bugs: Fix GDS mitigation select for
 non-ARCH_CAP_GDS_CTRL CPUs



> -----Original Message-----
> From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Sent: 2025年8月19日 1:33
> To: Li,Rongqing <lirongqing@...du.com>
> Cc: tglx@...utronix.de; bp@...en8.de; peterz@...radead.org;
> jpoimboe@...nel.org; mingo@...hat.com; dave.hansen@...ux.intel.com;
> x86@...nel.org; hpa@...or.com; david.kaplan@....com;
> linux-kernel@...r.kernel.org
> 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@...du.com>
> >
> > 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@...ux.intel.com>
> > Signed-off-by: Li RongQing <lirongqing@...du.com>
> 
> Reviewed-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>