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x86/speculation/mds: Add mds=full,nosmt cmdline option

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commit d71eb0ce10 upstream

Add the mds=full,nosmt cmdline option.  This is like mds=full, but with
SMT disabled if the CPU is vulnerable.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Josh Poimboeuf 2019-04-02 09:59:33 -05:00 committed by Greg Kroah-Hartman
parent a1f93c5387
commit 19ae10e543
3 changed files with 17 additions and 2 deletions
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3
Documentation/admin-guide/hw-vuln/mds.rst
View file

@ -260,6 +260,9 @@ time with the option "mds=". The valid arguments for this option are:
It does not automatically disable SMT.
full,nosmt The same as mds=full, with SMT disabled on vulnerable
CPUs. This is the complete mitigation.
off Disables MDS mitigations completely.
============ =============================================================

6
Documentation/admin-guide/kernel-parameters.txt
View file

@ -2230,8 +2230,10 @@
This parameter controls the MDS mitigation. The
options are:
full - Enable MDS mitigation on vulnerable CPUs
off - Unconditionally disable MDS mitigation
full - Enable MDS mitigation on vulnerable CPUs
full,nosmt - Enable MDS mitigation and disable
SMT on vulnerable CPUs
off - Unconditionally disable MDS mitigation
Not specifying this option is equivalent to
mds=full.

10
arch/x86/kernel/cpu/bugs.c
View file

@ -219,6 +219,7 @@ static void x86_amd_ssb_disable(void)
/* Default mitigation for L1TF-affected CPUs */
static enum mds_mitigations mds_mitigation __ro_after_init = MDS_MITIGATION_FULL;
static bool mds_nosmt __ro_after_init = false;
static const char * const mds_strings[] = {
[MDS_MITIGATION_OFF] = "Vulnerable",
@ -236,8 +237,13 @@ static void __init mds_select_mitigation(void)
if (mds_mitigation == MDS_MITIGATION_FULL) {
if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
mds_mitigation = MDS_MITIGATION_VMWERV;
static_branch_enable(&mds_user_clear);
if (mds_nosmt && !boot_cpu_has(X86_BUG_MSBDS_ONLY))
cpu_smt_disable(false);
}
pr_info("%s\n", mds_strings[mds_mitigation]);
}
@ -253,6 +259,10 @@ static int __init mds_cmdline(char *str)
mds_mitigation = MDS_MITIGATION_OFF;
else if (!strcmp(str, "full"))
mds_mitigation = MDS_MITIGATION_FULL;
else if (!strcmp(str, "full,nosmt")) {
mds_mitigation = MDS_MITIGATION_FULL;
mds_nosmt = true;
}
return 0;
}