linux-kernel - [PATCH 3.16 08/83] x86/speculation/mds: Apply more accurate check on hypervisor platform

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Date:   Wed, 20 Nov 2019 15:37:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Zhenzhong Duan" <zhenzhong.duan@...cle.com>,
        "Thomas Gleixner" <tglx@...utronix.de>
Subject: [PATCH 3.16 08/83] x86/speculation/mds: Apply more accurate check
 on hypervisor platform

3.16.78-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Zhenzhong Duan <zhenzhong.duan@...cle.com>

commit 517c3ba00916383af6411aec99442c307c23f684 upstream.

X86_HYPER_NATIVE isn't accurate for checking if running on native platform,
e.g. CONFIG_HYPERVISOR_GUEST isn't set or "nopv" is enabled.

Checking the CPU feature bit X86_FEATURE_HYPERVISOR to determine if it's
running on native platform is more accurate.

This still doesn't cover the platforms on which X86_FEATURE_HYPERVISOR is
unsupported, e.g. VMware, but there is nothing which can be done about this
scenario.

Fixes: 8a4b06d391b0 ("x86/speculation/mds: Add sysfs reporting for MDS")
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lkml.kernel.org/r/1564022349-17338-1-git-send-email-zhenzhong.duan@oracle.com
[bwh: Backported to 3.16: The old hypervisor check looked a bit different
 here.]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1349,12 +1349,10 @@ static ssize_t itlb_multihit_show_state(
 
 static ssize_t mds_show_state(char *buf)
 {
-#ifdef CONFIG_HYPERVISOR_GUEST
-	if (x86_hyper) {
+	if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
 		return sprintf(buf, "%s; SMT Host state unknown\n",
 			       mds_strings[mds_mitigation]);
 	}
-#endif
 
 	if (boot_cpu_has(X86_BUG_MSBDS_ONLY)) {
 		return sprintf(buf, "%s; SMT %s\n", mds_strings[mds_mitigation],