[PATCH] x86/cpuid: Introduce dom0-cpuid command line option

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Specifically, this lets the user opt in to non-default for dom0.

Split features[] out of parse_xen_cpuid(), giving it a lightly more
appropraite name, so it can be shared with parse_xen_cpuid().

Collect all dom0 settings together in dom0_{en,dis}able_feat[], and apply it
to dom0's policy when other tweaks are being made.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Daniel Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>

RFC, because I think we've got a preexisting error with late hwdom here.  We
really should not be cobbering a late hwdom's settings (which were provided in
the usual way by the toolstack in dom0).

Furthermore, the distinction gets more murky in a hyperlaunch future where
multiple domains may be constructed by Xen, and there is reason to expect that
a full toolstack-like configuration is made available for them.

One option might be to remove the special case from init_domain_cpuid_policy()
and instead make a call into the cpuid code from create_dom0().  It would have
to be placed between domain_create() and alloc_dom0_vcpu0() for dynamic sizing
of the FPU block to work.  Thoughts?
---
 docs/misc/xen-command-line.pandoc |  16 ++++++
 xen/arch/x86/cpuid.c              | 114 +++++++++++++++++++++++++++++++++-----
 2 files changed, 115 insertions(+), 15 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index f7797ea233f9..1278f9c27597 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -801,6 +801,22 @@ Controls for how dom0 is constructed on x86 systems.
 
     If using this option is necessary to fix an issue, please report a bug.
 
+### dom0-cpuid
+    = List of comma separated booleans
+
+    Applicability: x86
+
+This option allows for fine tuning of the facilities dom0 will use, after
+accounting for hardware capabilities and Xen settings as enumerated via CPUID.
+
+Options are accepted in positive and negative form, to enable or disable
+specific features.  All selections via this mechanism are subject to normal
+CPU Policy safety logic.
+
+This option is intended for developers to opt dom0 into non-default features,
+and is not intended for use in production circumstances.  If using this option
+is necessary to fix an issue, please report a bug.
+
 ### dom0-iommu
     = List of [ passthrough=<bool>, strict=<bool>, map-inclusive=<bool>,
                 map-reserved=<bool>, none ]
diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index 151944f65702..896bc1595317 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -26,17 +26,18 @@ static const uint32_t __initconst hvm_hap_def_featuremask[] 
=
     INIT_HVM_HAP_DEF_FEATURES;
 static const uint32_t deep_features[] = INIT_DEEP_FEATURES;
 
+static const struct feature_name {
+    const char *name;
+    unsigned int bit;
+} feature_names[] __initconstrel = INIT_FEATURE_NAMES;
+
 static int __init parse_xen_cpuid(const char *s)
 {
     const char *ss;
     int val, rc = 0;
 
     do {
-        static const struct feature {
-            const char *name;
-            unsigned int bit;
-        } features[] __initconstrel = INIT_FEATURE_NAMES;
-        const struct feature *lhs, *rhs, *mid = NULL /* GCC... */;
+        const struct feature_name *lhs, *rhs, *mid = NULL /* GCC... */;
         const char *feat;
 
         ss = strchr(s, ',');
@@ -49,8 +50,8 @@ static int __init parse_xen_cpuid(const char *s)
             feat += 3;
 
         /* (Re)initalise lhs and rhs for binary search. */
-        lhs = features;
-        rhs = features + ARRAY_SIZE(features);
+        lhs = feature_names;
+        rhs = feature_names + ARRAY_SIZE(feature_names);
 
         while ( lhs < rhs )
         {
@@ -97,6 +98,73 @@ static int __init parse_xen_cpuid(const char *s)
 }
 custom_param("cpuid", parse_xen_cpuid);
 
+static uint32_t __hwdom_initdata dom0_enable_feat[FSCAPINTS];
+static uint32_t __hwdom_initdata dom0_disable_feat[FSCAPINTS];
+
+static int __init parse_dom0_cpuid(const char *s)
+{
+    const char *ss;
+    int val, rc = 0;
+
+    do {
+        const struct feature_name *lhs, *rhs, *mid = NULL /* GCC... */;
+        const char *feat;
+
+        ss = strchr(s, ',');
+        if ( !ss )
+            ss = strchr(s, '\0');
+
+        /* Skip the 'no-' prefix for name comparisons. */
+        feat = s;
+        if ( strncmp(s, "no-", 3) == 0 )
+            feat += 3;
+
+        /* (Re)initalise lhs and rhs for binary search. */
+        lhs = feature_names;
+        rhs = feature_names + ARRAY_SIZE(feature_names);
+
+        while ( lhs < rhs )
+        {
+            int res;
+
+            mid = lhs + (rhs - lhs) / 2;
+            res = cmdline_strcmp(feat, mid->name);
+
+            if ( res < 0 )
+            {
+                rhs = mid;
+                continue;
+            }
+            if ( res > 0 )
+            {
+                lhs = mid + 1;
+                continue;
+            }
+
+            if ( (val = parse_boolean(mid->name, s, ss)) >= 0 )
+            {
+                __set_bit(mid->bit,
+                          val ? dom0_enable_feat : dom0_disable_feat);
+                mid = NULL;
+            }
+
+            break;
+        }
+
+        /*
+         * Mid being NULL means that the name and boolean were successfully
+         * identified.  Everything else is an error.
+         */
+        if ( mid )
+            rc = -EINVAL;
+
+        s = ss + 1;
+    } while ( *ss );
+
+    return rc;
+}
+custom_param("dom0-cpuid", parse_dom0_cpuid);
+
 #define EMPTY_LEAF ((struct cpuid_leaf){})
 static void zero_leaves(struct cpuid_leaf *l,
                         unsigned int first, unsigned int last)
@@ -727,17 +795,33 @@ int init_domain_cpuid_policy(struct domain *d)
     if ( !p )
         return -ENOMEM;
 
-    /* The hardware domain can't migrate.  Give it ITSC if available. */
     if ( is_hardware_domain(d) )
+    {
+        uint32_t fs[FSCAPINTS];
+        unsigned int i;
+
+        /* The hardware domain can't migrate.  Give it ITSC if available. */
         p->extd.itsc = cpu_has_itsc;
 
-    /*
-     * Expose the "hardware speculation behaviour" bits of ARCH_CAPS to dom0,
-     * so dom0 can turn off workarounds as appropriate.  Temporary, until the
-     * domain policy logic gains a better understanding of MSRs.
-     */
-    if ( is_hardware_domain(d) && cpu_has_arch_caps )
-        p->feat.arch_caps = true;
+        /*
+         * Expose the "hardware speculation behaviour" bits of ARCH_CAPS to
+         * dom0, so dom0 can turn off workarounds as appropriate.  Temporary,
+         * until the domain policy logic gains a better understanding of MSRs.
+         */
+        if ( cpu_has_arch_caps )
+            p->feat.arch_caps = true;
+
+        /* Apply dom0-cpuid= command line settings. */
+        cpuid_policy_to_featureset(p, fs);
+
+        for ( i = 0; i < ARRAY_SIZE(fs); ++i )
+        {
+            fs[i] |= dom0_enable_feat[i];
+            fs[i] &= ~dom0_disable_feat[i];
+        }
+
+        cpuid_featureset_to_policy(fs, p);
+    }
 
     d->arch.cpuid = p;
 
-- 
2.11.0