linux-kernel - [PATCH v2] x86/cpuinfo: Clear X86_FEATURE

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Message-Id: <20220704142250.1512726-1-martin.fernandez@eclypsium.com>
Date:   Mon,  4 Jul 2022 11:22:51 -0300
From:   Martin Fernandez <martin.fernandez@...ypsium.com>
To:     linux-kernel@...r.kernel.org
Cc:     bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        mingo@...hat.com, tglx@...utronix.de,
        kirill.shutemov@...ux.intel.com, daniel.gutson@...ypsium.com,
        hughsient@...il.com, alex.bazhaniuk@...ypsium.com,
        Martin Fernandez <martin.fernandez@...ypsium.com>
Subject: [PATCH v2] x86/cpuinfo: Clear X86_FEATURE_TME if TME/MKTME is disabled by BIOS

Right now the only way to check this is by greping the kernel logs,
which is inconvenient. This is currently checked for fwupd for
example.

I understand that cpuinfo is supposed to report every feature in the
cpu but since AMD is doing the same (and it also broke backwards
compatibility [1]) for sme/sev I think it's good to have this for
Intel too.

Another option to prevent greping the logs would be a file in
sysfs. I'm open to suggestions to where to place this infomartion. I
saw a proposal about a firmware security filesystem [2]; that would
fit perfectly.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/patch/?id=08f253ec3767bcfafc5d32617a92cee57c63968e

[2] https://lore.kernel.org/all/20220622215648.96723-3-nayna@linux.ibm.com/

Changelog since v1

Clear the flag not only for BSP but for every cpu in the system.

Signed-off-by: Martin Fernandez <martin.fernandez@...ypsium.com>
---
 arch/x86/kernel/cpu/intel.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index fd5dead8371c..17f23e23f911 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -570,6 +570,7 @@ static void detect_tme(struct cpuinfo_x86 *c)

 	if (!TME_ACTIVATE_LOCKED(tme_activate) || !TME_ACTIVATE_ENABLED(tme_activate)) {
 		pr_info_once("x86/tme: not enabled by BIOS\n");
+		clear_cpu_cap(c, X86_FEATURE_TME);
 		mktme_status = MKTME_DISABLED;
 		return;
 	}
--
2.30.2