Revert "x86/spec_ctrl: Add 'nolfence' knob to disable fallback for spectre_v2 mitigation"

This reverts commit f51532c93e3359743f0f8e226f1503123d3b1ae5.

And also other pieces of code that would use this.

Orabug: 27601789
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7f3662353206048499cdc1b0b211ea129d0f2d48..b1a5084b0455b702958fb31f4646a6c1088db27d 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2357,19 +2357,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
        noibrs          [X86]
                        Don't use indirect branch restricted speculation (IBRS)
                        feature when running in secure environment,
-                       to avoid performance overhead. Disabling this will fallback
-                       on using lfence.
+                       to avoid performance overhead.
 
        noibpb          [X86]
                        Don't use indirect branch prediction barrier (IBPB)
                        feature when running in secure environment,
                        to avoid performance overhead.
 
-       nolfence        [X86]
-                       Don't use lfence on every system call/interrupt/exception
-                       if noibrs has been specified. This is used to avoid
-                       performance overhead.
-
        nosmap          [X86]
                        Disable SMAP (Supervisor Mode Access Prevention)
                        even if it is supported by processor.

diff --git a/arch/x86/include/asm/spec_ctrl.h b/arch/x86/include/asm/spec_ctrl.h
index 4d3577c54e514b363d6ccf19a9192a5e9325f515..66424e6b4c373f8ace2142143bdca8e89992a256 100644 (file)
--- a/arch/x86/include/asm/spec_ctrl.h
+++ b/arch/x86/include/asm/spec_ctrl.h
@@ -9,7 +9,7 @@
 #define SPEC_CTRL_IBRS_INUSE           (1<<0)  /* OS enables IBRS usage */
 #define SPEC_CTRL_IBRS_SUPPORTED       (1<<1)  /* System supports IBRS */
 #define SPEC_CTRL_IBRS_ADMIN_DISABLED  (1<<2)  /* Admin disables IBRS */
-#define SPEC_CTRL_LFENCE_OFF           (1<<3)  /* No lfence */
+
 #ifdef __ASSEMBLY__
 
 .extern use_ibrs
@@ -133,8 +133,6 @@
        __ASM_ENABLE_IBRS
        jmp     20f
 7:
-       testl  $SPEC_CTRL_LFENCE_OFF, use_ibrs
-       jnz     20f
        lfence
 20:
 .endm
@@ -145,8 +143,6 @@
        __ASM_ENABLE_IBRS_CLOBBER
        jmp     21f
 11:
-       testl  $SPEC_CTRL_LFENCE_OFF, use_ibrs
-       jnz     21f
        lfence
 21:
 .endm
@@ -165,8 +161,6 @@
        jmp 22f
 12:
        movl $SPEC_CTRL_FEATURE_ENABLE_IBRS, \save_reg
-       testl  $SPEC_CTRL_LFENCE_OFF, use_ibrs
-       jnz     22f
        lfence
 22:
 .endm
@@ -184,8 +178,6 @@
        wrmsr
        jmp 23f
 13:
-       testl  $SPEC_CTRL_LFENCE_OFF, use_ibrs
-       jnz     23f
        lfence
 23:
 .endm
@@ -266,15 +258,6 @@ static inline void clear_ibrs_disabled(void)
        sysctl_ibrs_enabled = ibrs_inuse ? 1 : 0;
 }
 
-extern u32 sysctl_lfence_enabled;
-
-#define lfence_inuse (!(use_ibrs & SPEC_CTRL_LFENCE_OFF))
-
-static inline void set_lfence_disabled(void)
-{
-       use_ibrs |= SPEC_CTRL_LFENCE_OFF;
-}
-
 /* indicate usage of IBPB to control execution speculation */
 extern int use_ibpb;
 extern u32 sysctl_ibpb_enabled;

diff --git a/arch/x86/kernel/cpu/bugs_64.c b/arch/x86/kernel/cpu/bugs_64.c
index 6fbbdee42cfa47e594f166b6e14adaf8aa4ec157..c38997a0d2273758249543d21c44a54435a3652a 100644 (file)
--- a/arch/x86/kernel/cpu/bugs_64.c
+++ b/arch/x86/kernel/cpu/bugs_64.c
@@ -138,7 +138,6 @@ static const char *spectre_v2_strings[] = {
        [SPECTRE_V2_RETPOLINE_GENERIC]          = "Mitigation: Full generic retpoline",
        [SPECTRE_V2_RETPOLINE_AMD]              = "Mitigation: Full AMD retpoline",
        [SPECTRE_V2_IBRS]                       = "Mitigation: IBRS",
-       [SPECTRE_V2_IBRS_LFENCE]                = "Mitigation: lfence",
 
 };
 
@@ -177,14 +176,7 @@ int refresh_set_spectre_v2_enabled(void)
        if (check_ibrs_inuse())
                spectre_v2_enabled = SPECTRE_V2_IBRS;
        else {
-               /*
-                * If that didn't work (say no microcode or noibrs), we end up using
-                * lfence on system calls/exceptions/parameters.
-                */
-               if (lfence_inuse)
-                       spectre_v2_enabled = SPECTRE_V2_IBRS_LFENCE;
-               else
-                       spectre_v2_enabled = SPECTRE_V2_NONE;
+               spectre_v2_enabled = SPECTRE_V2_NONE;
        }
 
        return true;
@@ -227,10 +219,6 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
                set_ibpb_disabled();
        }
 
-       if (cmdline_find_option_bool(boot_command_line, "nolfence")) {
-               set_lfence_disabled();
-       }
-
        ret = cmdline_find_option(boot_command_line, "spectre_v2", arg,
                                  sizeof(arg));
        if (ret > 0)  {
@@ -273,18 +261,10 @@ static enum spectre_v2_mitigation __init ibrs_select(void)
        /* If it is ON, OK, lets use it.*/
        if (check_ibrs_inuse())
                mode = SPECTRE_V2_IBRS;
-       else {
-               /*
-                * If that didn't work (say no microcode or noibrs), we end up using
-                * lfence on system calls/exceptions/parameters.
-                */
-               if (lfence_inuse)
-                       mode = SPECTRE_V2_IBRS_LFENCE;
-       }
 
        if (mode == SPECTRE_V2_NONE)
                /* Well, fallback on automatic discovery. */
-               pr_info("IBRS and lfence could not be enabled.\n");
+               pr_info("IBRS could not be enabled.\n");
        else {
                /* OK, some form of IBRS is enabled, lets see if we need to STUFF_RSB */
                if (!boot_cpu_has(X86_FEATURE_SMEP))
@@ -308,7 +288,6 @@ static void __init disable_ibrs_and_friends(bool disable_ibpb)
        /* We need to use IBPB with retpoline if it is available. */
        if (disable_ibpb)
                set_ibpb_disabled();
-       set_lfence_disabled();
 }
 
 static bool __init retpoline_selected(enum spectre_v2_mitigation_cmd cmd)