[Xen-devel] [PATCH v2] x86/spec-ctrl: Yet more fixes for xpti= parsing

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

As it currently stands, 'xpti=dom0' is indistinguishable from the default
value, which means it will be overridden by ARCH_CAPABILITIES_RDCL_NO on fixed
hardware.

Switch opt_xpti to use -1 as a default like all our other related options, and
clobber it as soon as we have a string to parse.

In addition, 'xpti' alone should be interpreted in its positive boolean form,
rather than resulting in a parse error.

  (XEN) parameter "xpti" has invalid value "", rc=-22!

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>

v2:
 * Don't intepret "xpti=dom0," as "xpti"
---
 xen/arch/x86/spec_ctrl.c        | 15 +++++++++++----
 xen/include/asm-x86/spec_ctrl.h |  2 +-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 32a4ea6..32213ac 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -420,8 +420,7 @@ static bool __init should_use_eager_fpu(void)
     }
 }
 
-#define OPT_XPTI_DEFAULT  0xff
-uint8_t __read_mostly opt_xpti = OPT_XPTI_DEFAULT;
+int8_t __read_mostly opt_xpti = -1;
 
 static __init void xpti_init_default(uint64_t caps)
 {
@@ -439,6 +438,14 @@ static __init int parse_xpti(const char *s)
     const char *ss;
     int val, rc = 0;
 
+    /* Inhibit the defaults as an explicit choice has been given. */
+    if ( opt_xpti == -1 )
+        opt_xpti = 0;
+
+    /* Interpret 'xpti' alone in its positive boolean form. */
+    if ( *s == '\0' )
+        opt_xpti = OPT_XPTI_DOM0 | OPT_XPTI_DOMU;
+
     do {
         ss = strchr(s, ',');
         if ( !ss )
@@ -456,7 +463,7 @@ static __init int parse_xpti(const char *s)
 
         default:
             if ( !strcmp(s, "default") )
-                opt_xpti = OPT_XPTI_DEFAULT;
+                opt_xpti = -1;
             else if ( (val = parse_boolean("dom0", s, ss)) >= 0 )
                 opt_xpti = (opt_xpti & ~OPT_XPTI_DOM0) |
                            (val ? OPT_XPTI_DOM0 : 0);
@@ -618,7 +625,7 @@ void __init init_speculation_mitigations(void)
     if ( default_xen_spec_ctrl )
         setup_force_cpu_cap(X86_FEATURE_SC_MSR_IDLE);
 
-    if ( opt_xpti == OPT_XPTI_DEFAULT )
+    if ( opt_xpti == -1 )
         xpti_init_default(caps);
 
     if ( opt_xpti == 0 )
diff --git a/xen/include/asm-x86/spec_ctrl.h b/xen/include/asm-x86/spec_ctrl.h
index 5b40afb..fea8260 100644
--- a/xen/include/asm-x86/spec_ctrl.h
+++ b/xen/include/asm-x86/spec_ctrl.h
@@ -34,7 +34,7 @@ extern bool bsp_delay_spec_ctrl;
 extern uint8_t default_xen_spec_ctrl;
 extern uint8_t default_spec_ctrl_flags;
 
-extern uint8_t opt_xpti;
+extern int8_t opt_xpti;
 #define OPT_XPTI_DOM0  0x01
 #define OPT_XPTI_DOMU  0x02
 
-- 
2.1.4


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