[Xen-changelog] [xen stable-4.9] x86/spec-ctrl: Fix the parsing of xpti= on fixed Intel hardware

[patchbot@xxxxxxx]

commit a1b223b756f354895525060bd3f9f1f07899a082
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Jul 30 11:57:24 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jul 30 11:57:24 2018 +0200

    x86/spec-ctrl: Fix the parsing of xpti= on fixed Intel hardware
    
    The calls to xpti_init_default() in parse_xpti() are buggy.  The CPUID data
    hasn't been fetched that early, and boot_cpu_has(X86_FEATURE_ARCH_CAPS) will
    always evaluate false.
    
    As a result, the default case won't disable XPTI on Intel hardware which
    advertises ARCH_CAPABILITIES_RDCL_NO.
    
    Simplify parse_xpti() to solely the setting of opt_xpti according to the
    passed string, and have init_speculation_mitigations() call
    xpti_init_default() if appropiate.  Drop the force parameter, and pass caps
    instead, to avoid redundant re-reading of MSR_ARCH_CAPS.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Wei Liu <wei.liu2@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: be5e2ff6f54e0245331ed360b8786760f82fd673
    master date: 2018-07-24 11:25:54 +0100
---
 xen/arch/x86/spec_ctrl.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 4f62febb6a..11c05b9042 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -407,17 +407,10 @@ static bool __init should_use_eager_fpu(void)
 #define OPT_XPTI_DEFAULT  0xff
 uint8_t __read_mostly opt_xpti = OPT_XPTI_DEFAULT;
 
-static __init void xpti_init_default(bool force)
+static __init void xpti_init_default(uint64_t caps)
 {
-    uint64_t caps = 0;
-
-    if ( !force && (opt_xpti != OPT_XPTI_DEFAULT) )
-        return;
-
     if ( boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
         caps = ARCH_CAPABILITIES_RDCL_NO;
-    else if ( boot_cpu_has(X86_FEATURE_ARCH_CAPS) )
-        rdmsrl(MSR_ARCH_CAPABILITIES, caps);
 
     if ( caps & ARCH_CAPABILITIES_RDCL_NO )
         opt_xpti = 0;
@@ -430,8 +423,6 @@ static __init int parse_xpti(char *s)
     char *ss;
     int val, rc = 0;
 
-    xpti_init_default(false);
-
     do {
         ss = strchr(s, ',');
         if ( ss )
@@ -449,7 +440,7 @@ static __init int parse_xpti(char *s)
 
         default:
             if ( !strcmp(s, "default") )
-                xpti_init_default(true);
+                opt_xpti = OPT_XPTI_DEFAULT;
             else if ( (val = parse_boolean("dom0", s, ss)) >= 0 )
                 opt_xpti = (opt_xpti & ~OPT_XPTI_DOM0) |
                            (val ? OPT_XPTI_DOM0 : 0);
@@ -611,7 +602,9 @@ void __init init_speculation_mitigations(void)
     if ( default_xen_spec_ctrl )
         setup_force_cpu_cap(X86_FEATURE_SC_MSR_IDLE);
 
-    xpti_init_default(false);
+    if ( opt_xpti == OPT_XPTI_DEFAULT )
+        xpti_init_default(caps);
+
     if ( opt_xpti == 0 )
         setup_force_cpu_cap(X86_FEATURE_NO_XPTI);
     else
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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