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Commit f7a119a7 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Greg Kroah-Hartman
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x86/speculation/mds: Add mds=full,nosmt cmdline option 



commit d71eb0ce109a124b0fa714832823b9452f2762cf 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: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarTyler Hicks <tyhicks@canonical.com>
Acked-by: default avatarJiri Kosina <jkosina@suse.cz>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent cfaa3d76

Documentation/admin-guide/hw-vuln/mds.rst

+3 −0
Original line number Diff line number Diff line
@@ -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.



  ============  =============================================================

Documentation/admin-guide/kernel-parameters.txt

+4 −2
Original line number Diff line number Diff line
@@ -2336,6 +2336,8 @@ 
			options are:



			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

arch/x86/kernel/cpu/bugs.c

+10 −0
Original line number Diff line number Diff line
@@ -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;

}