linux-kernel - RE: [PATCH v2] x86/mm: Don't disable INVLPG if "incomplete Global INVLPG flushes" is fixed by microcode

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Message-ID:
 <SN6PR02MB41576028614CB7FE9A11EBEBD4362@SN6PR02MB4157.namprd02.prod.outlook.com>
Date: Mon, 25 Mar 2024 04:57:33 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Xi Ruoyao <xry111@...111.site>, Dave Hansen <dave.hansen@...ux.intel.com>
CC: Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Dexuan Cui <decui@...rosoft.com>
Subject: RE: [PATCH v2] x86/mm: Don't disable INVLPG if "incomplete Global
 INVLPG flushes" is fixed by microcode

From: Xi Ruoyao <xry111@...111.site> Sent: Sunday, March 24, 2024 12:05 PM
> 
> Per the "Processor Specification Update" documentations referred by the
> intel-microcode-20240312 release note, this microcode release has fixed
> the issue for all affected models.
> 
> So don't disable INVLPG if the microcode is new enough.
> 
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Xi Ruoyao <xry111@...111.site>
> ---
>  arch/x86/mm/init.c | 32 ++++++++++++++++++++------------
>  1 file changed, 20 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 679893ea5e68..c52be4e66e44 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -261,33 +261,41 @@ static void __init probe_page_size_mask(void)
>  	}
>  }
> 
> -#define INTEL_MATCH(_model) { .vendor  = X86_VENDOR_INTEL,	\
> -			      .family  = 6,			\
> -			      .model = _model,			\
> -			    }
> +#define INTEL_MATCH(_model, _fixed_microcode)	\
> +    { .vendor		= X86_VENDOR_INTEL,	\
> +      .family		= 6,			\
> +      .model		= _model,		\
> +      .driver_data	= _fixed_microcode,	\
> +    }
> +
>  /*
>   * INVLPG may not properly flush Global entries
> - * on these CPUs when PCIDs are enabled.
> + * on these CPUs when PCIDs are enabled and the
> + * microcode is not updated to fix the issue.
>   */
>  static const struct x86_cpu_id invlpg_miss_ids[] = {
> -	INTEL_MATCH(INTEL_FAM6_ALDERLAKE   ),
> -	INTEL_MATCH(INTEL_FAM6_ALDERLAKE_L ),
> -	INTEL_MATCH(INTEL_FAM6_ATOM_GRACEMONT ),
> -	INTEL_MATCH(INTEL_FAM6_RAPTORLAKE  ),
> -	INTEL_MATCH(INTEL_FAM6_RAPTORLAKE_P),
> -	INTEL_MATCH(INTEL_FAM6_RAPTORLAKE_S),
> +	INTEL_MATCH(INTEL_FAM6_ALDERLAKE,	0x34),
> +	INTEL_MATCH(INTEL_FAM6_ALDERLAKE_L,	0x432),
> +	INTEL_MATCH(INTEL_FAM6_ATOM_GRACEMONT,	0x15),
> +	INTEL_MATCH(INTEL_FAM6_RAPTORLAKE,	0x122),
> +	INTEL_MATCH(INTEL_FAM6_RAPTORLAKE_P,	0x4121),
> +	INTEL_MATCH(INTEL_FAM6_RAPTORLAKE_S,	0x34),
>  	{}
>  };
> 
>  static void setup_pcid(void)
>  {
> +	const struct x86_cpu_id *invlpg_miss_match;
> +
>  	if (!IS_ENABLED(CONFIG_X86_64))
>  		return;
> 
>  	if (!boot_cpu_has(X86_FEATURE_PCID))
>  		return;
> 
> -	if (x86_match_cpu(invlpg_miss_ids)) {
> +	invlpg_miss_match = x86_match_cpu(invlpg_miss_ids);
> +	if (invlpg_miss_match &&
> +	    invlpg_miss_match->driver_data > boot_cpu_data.microcode) {
>  		pr_info("Incomplete global flushes, disabling PCID");
>  		setup_clear_cpu_cap(X86_FEATURE_PCID);
>  		return;

As noted in similar places where microcode versions are
checked, hypervisors often lie to guests about microcode versions.
For example, see comments in bad_spectre_microcode().  I
know Hyper-V guests always see the microcode version as
0xFFFFFFFF (max u32 value).  So in a Hyper-V guest the above
code will always leave PCID enabled.

Maybe the above should have a check for running on a
hypervisor and always disable PCID without checking the
microcode version.  That's the safe approach, though there are
other similar cases like bad_spectre_microcode() that take
the unsafe approach when running as a guest.  I don't know
what's best here .....

Michael