[Xen-devel] [PATCH 1/9] x86/spec-ctrl: Drop the bti= command line option

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

bti= was introduced with the original Spectre fixes (Jan 2018), but by the
time Speculative Store Bypass came along (May 2018), it was superceeded by the
more generic spec-ctrl=.

Since then, we've had LazyFPU (June 2018) and L1TF (August 2018), which means
noone will be using the option.  Remove it entirely - anyone who happens to
accidentially be using it might now spot Xen complaining about an option it
doesn't understand.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 docs/misc/xen-command-line.markdown | 34 ----------------------
 xen/arch/x86/spec_ctrl.c            | 57 -------------------------------------
 2 files changed, 91 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index 9028bcd..764f33a 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -250,40 +250,6 @@ and not running softirqs. Reduce this if softirqs are not 
being run frequently
 enough. Setting this to a high value may cause boot failure, particularly if
 the NMI watchdog is also enabled.
 
-### bti (x86)
-> `= List of [ <bool>, thunk=retpoline|lfence|jmp, ibrs=<bool>, ibpb=<bool>, 
rsb=<bool>, rsb_{vmexit,native}=<bool> ]`
-
-**WARNING: This command line option is deprecated, and superseded by
-_spec-ctrl=_ - using both options in combination is undefined.**
-
-Branch Target Injection controls.  By default, Xen will pick the most
-appropriate BTI mitigations based on compiled in support, loaded microcode,
-and hardware details.
-
-**WARNING: Any use of this option may interfere with heuristics.  Use with
-extreme care.**
-
-A (negative) boolean value can be specified to turn off all mitigations.
-(Use of a positive boolean value is invalid.)
-
-If Xen was compiled with INDIRECT\_THUNK support, `thunk=` can be used to
-select which of the thunks gets patched into the `__x86_indirect_thunk_%reg`
-locations.  The default thunk is `retpoline` (generally preferred for Intel
-hardware), with the alternatives being `jmp` (a `jmp *%reg` gadget, minimal
-overhead), and `lfence` (an `lfence; jmp *%reg` gadget, preferred for AMD).
-
-On hardware supporting IBRS, the `ibrs=` option can be used to force or
-prevent Xen using the feature itself.  If Xen is not using IBRS itself,
-functionality is still set up so IBRS can be virtualised for guests.
-
-On hardware supporting IBPB, the `ibpb=` option can be used to prevent Xen
-from issuing Branch Prediction Barriers on vcpu context switches.
-
-The `rsb=`, `rsb_vmexit=` and `rsb_native=` options can be used to control
-when the RSB gets overwritten.  The former control all RSB overwriting, while
-the latter two can be used to fine tune overwriting on from HVM context, and
-an entry from a native (PV or Xen) context.
-
 ### clocksource (x86)
 > `= pit | hpet | acpi | tsc`
 
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index b5e77bd..a36bcef 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -59,63 +59,6 @@ paddr_t __read_mostly l1tf_addr_mask, __read_mostly 
l1tf_safe_maddr;
 static bool __initdata cpu_has_bug_l1tf;
 static unsigned int __initdata l1d_maxphysaddr;
 
-static int __init parse_bti(const char *s)
-{
-    const char *ss;
-    int val, rc = 0;
-
-    do {
-        ss = strchr(s, ',');
-        if ( !ss )
-            ss = strchr(s, '\0');
-
-        val = parse_bool(s, ss);
-        if ( !val )
-        {
-            opt_thunk = THUNK_JMP;
-            opt_ibrs = 0;
-            opt_ibpb = false;
-            opt_rsb_pv = false;
-            opt_rsb_hvm = false;
-        }
-        else if ( val > 0 )
-            rc = -EINVAL;
-        else if ( !strncmp(s, "thunk=", 6) )
-        {
-            s += 6;
-
-            if ( !strncmp(s, "retpoline", ss - s) )
-                opt_thunk = THUNK_RETPOLINE;
-            else if ( !strncmp(s, "lfence", ss - s) )
-                opt_thunk = THUNK_LFENCE;
-            else if ( !strncmp(s, "jmp", ss - s) )
-                opt_thunk = THUNK_JMP;
-            else
-                rc = -EINVAL;
-        }
-        else if ( (val = parse_boolean("ibrs", s, ss)) >= 0 )
-            opt_ibrs = val;
-        else if ( (val = parse_boolean("ibpb", s, ss)) >= 0 )
-            opt_ibpb = val;
-        else if ( (val = parse_boolean("rsb_native", s, ss)) >= 0 )
-            opt_rsb_pv = val;
-        else if ( (val = parse_boolean("rsb_vmexit", s, ss)) >= 0 )
-            opt_rsb_hvm = val;
-        else if ( (val = parse_boolean("rsb", s, ss)) >= 0 )
-        {
-            opt_rsb_pv = val;
-            opt_rsb_hvm = val;
-        }
-        else
-            rc = -EINVAL;
-
-        s = ss + 1;
-    } while ( *ss );
-
-    return rc;
-}
-custom_param("bti", parse_bti);
-
 static int __init parse_spec_ctrl(const char *s)
 {
     const char *ss;
-- 
2.1.4


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