linux-kernel - RE: Re: [????] Re: [PATCH] x86/bugs: Fix GDS mitigation check for CPUs without ARCH_CAP_GDS

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Message-ID: <2a53cf1c48b44ea4b12debeed7521d50@baidu.com>
Date: Sat, 16 Aug 2025 00:15:20 +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: [????] Re: [PATCH] x86/bugs: Fix GDS mitigation check for
 CPUs without ARCH_CAP_GDS_CTRL


> 
> How is that a problem? That is how it was originally implemented.
> 
> Infact, the following checks are required for the correct behavior:


You are right, I will resend this patch

Thanks

-Li

> 
>          if (mcu_ctrl & GDS_MITG_LOCKED) {
>                  if (gds_mitigation == GDS_MITIGATION_OFF)
>                          pr_warn("Mitigation locked. Disable failed.\n");
> 	...
>                  gds_mitigation = GDS_MITIGATION_FULL_LOCKED;
>          }
> 
> If the GDS microcode mitigation is locked before the kernel boot, MSR write for
> OFF will not take effect anyways. And you report OFF when the mitigation is
> locked to ON. While also triggering below WARN_ON_ONCE():
> 
> update_gds_msr()
> {
> ...
>          /*
>           * Check to make sure that the WRMSR value was not ignored.
> Writes to
>           * GDS_MITG_DIS will be ignored if this processor is locked but the
> boot
>           * processor was not.
>           */
>          rdmsrq(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl_after);
>          WARN_ON_ONCE(mcu_ctrl != mcu_ctrl_after);