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From:   Kai Huang <kai.huang@intel.com>
To:     linux-sgx@vger.kernel.org
Cc:     dave.hansen@linux.intel.com, seanjc@google.com, jarkko@kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] x86/intel: Clear SGX bit if both SGX driver and KVM SGX are not enabled
Date:   Fri,  9 Sep 2022 20:08:53 +1200
Message-Id: <20220909080853.547058-1-kai.huang@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Currently on platform which has SGX enabled, if CONFIG_X86_SGX is not
enabled, the X86_FEATURE_SGX is not cleared, resulting in /proc/cpuinfo
shows "sgx" feature.  This is not desired.

Clear SGX feature bit if both SGX driver and KVM SGX are not enabled in
init_ia32_feat_ctl().

Signed-off-by: Kai Huang <kai.huang@intel.com>
---

Hi Dave, Sean, Jarkko,

Could you help to review?  Tested on SGX (BIOS) enabled machine with
CONFIG_X86_SGX unset.

This patch is generated on latest tip/master, but it applies to
tip/x86/sgx cleanly as well.

---
 arch/x86/kernel/cpu/feat_ctl.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
index 993697e71854..2f67409f5f00 100644
--- a/arch/x86/kernel/cpu/feat_ctl.c
+++ b/arch/x86/kernel/cpu/feat_ctl.c
@@ -191,6 +191,19 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
 		return;
 	}
 
+	/*
+	 * By reaching here, it is certain that:
+	 *  - CPU supports SGX.
+	 *  - SGX is enabled by BIOS.
+	 *
+	 * However if both SGX driver and KVM SGX are not enabled, just
+	 * need to clear SGX feature bit.
+	 */
+	if (!enable_sgx_driver && !enable_sgx_kvm) {
+		clear_cpu_cap(c, X86_FEATURE_SGX);
+		return;
+	}
+
 	/*
 	 * VMX feature bit may be cleared due to being disabled in BIOS,
 	 * in which case SGX virtualization cannot be supported either.

base-commit: b8b09110cf290fdab4006b717da7a776ffb0cb73
-- 
2.37.1