[Xen-devel] [PATCH v2 08/30] xen/x86: Mask out unknown features from Xen's capabilities

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

If Xen doesn't know about a feature, it is unsafe for use and should be
deliberately hidden from Xen's capabilities.

This doesn't make a practical difference yet, but will make a difference
later when the guest featuresets are seeded from the host featureset.

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

v2:
 * Reduced substantially from v1, by using the autogenerated information.
---
 xen/arch/x86/Makefile            |  1 +
 xen/arch/x86/cpu/common.c        |  3 +++
 xen/arch/x86/cpuid.c             | 19 +++++++++++++++++++
 xen/include/asm-x86/cpufeature.h |  3 +--
 xen/include/asm-x86/cpuid.h      | 24 ++++++++++++++++++++++++
 xen/tools/gen-cpuid.py           | 24 ++++++++++++++++++++++++
 6 files changed, 72 insertions(+), 2 deletions(-)
 create mode 100644 xen/arch/x86/cpuid.c
 create mode 100644 xen/include/asm-x86/cpuid.h

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 8e6e901..0e2b1d5 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -12,6 +12,7 @@ obj-y += bitops.o
 obj-bin-y += bzimage.init.o
 obj-bin-y += clear_page.o
 obj-bin-y += copy_page.o
+obj-y += cpuid.o
 obj-y += compat.o x86_64/compat.o
 obj-$(CONFIG_KEXEC) += crash.o
 obj-y += debug.o
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index a99cc7c..151dfe4 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -341,6 +341,9 @@ void identify_cpu(struct cpuinfo_x86 *c)
         * The vendor-specific functions might have changed features.  Now
         * we do "generic changes."
         */
+       for (i = 0; i < FSCAPINTS; ++i) {
+               c->x86_capability[i] &= known_features[i];
+       }
 
        for (i = 0 ; i < NCAPINTS ; ++i)
                c->x86_capability[i] &= ~cleared_caps[i];
diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
new file mode 100644
index 0000000..fb3a6ac
--- /dev/null
+++ b/xen/arch/x86/cpuid.c
@@ -0,0 +1,19 @@
+#include <xen/lib.h>
+#include <asm/cpuid.h>
+
+const uint32_t known_features[] = INIT_KNOWN_FEATURES;
+
+static void __maybe_unused build_assertions(void)
+{
+    BUILD_BUG_ON(ARRAY_SIZE(known_features) != FSCAPINTS);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h
index d069563..a984a81 100644
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -13,9 +13,8 @@
 
 #include <public/arch-x86/cpufeatureset.h>
 
-#include <asm/cpuid-autogen.h>
+#include <asm/cpuid.h>
 
-#define FSCAPINTS FEATURESET_NR_ENTRIES
 #define NCAPINTS (FSCAPINTS + 1) /* N 32-bit words worth of info */
 
 /* Other features, Linux-defined mapping, FSMAX+1 */
diff --git a/xen/include/asm-x86/cpuid.h b/xen/include/asm-x86/cpuid.h
new file mode 100644
index 0000000..6cca5ea
--- /dev/null
+++ b/xen/include/asm-x86/cpuid.h
@@ -0,0 +1,24 @@
+#ifndef __X86_CPUID_H__
+#define __X86_CPUID_H__
+
+#include <asm/cpuid-autogen.h>
+
+#define FSCAPINTS FEATURESET_NR_ENTRIES
+
+#ifndef __ASSEMBLY__
+#include <xen/types.h>
+
+extern const uint32_t known_features[FSCAPINTS];
+
+#endif /* __ASSEMBLY__ */
+#endif /* !__X86_CPUID_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/tools/gen-cpuid.py b/xen/tools/gen-cpuid.py
index c8240c0..0843be6 100755
--- a/xen/tools/gen-cpuid.py
+++ b/xen/tools/gen-cpuid.py
@@ -19,6 +19,8 @@ class State(object):
 
         # State calculated
         self.nr_entries = 0 # Number of words in a featureset
+        self.common = 0 # Common features between 1d and e1d
+        self.known = [] # All known features
 
 def parse_definitions(state):
     """
@@ -89,6 +91,22 @@ def crunch_numbers(state):
     # Size of bitmaps
     state.nr_entries = nr_entries = (max(state.names.keys()) >> 5) + 1
 
+    # Features common between 1d and e1d.
+    common_1d = (FPU, VME, DE, PSE, TSC, MSR, PAE, MCE, CX8, APIC,
+                 MTRR, PGE, MCA, CMOV, PAT, PSE36, MMX, FXSR)
+
+    # All known features.  Duplicate the common features in e1d
+    e1d_base = (SYSCALL >> 5) << 5
+    state.known = featureset_to_uint32s(
+        state.names.keys() + [ e1d_base + (x % 32) for x in common_1d ],
+        nr_entries)
+
+    # Fold common back into names
+    for f in common_1d:
+        state.names[e1d_base + (f % 32)] = "E1D_" + state.names[f]
+
+    state.common = featureset_to_uint32s(common_1d, 1)[0]
+
 
 def write_results(state):
     state.output.write(
@@ -103,7 +121,13 @@ def write_results(state):
     state.output.write(
 """
 #define FEATURESET_NR_ENTRIES %s
+
+#define INIT_COMMON_FEATURES %s
+
+#define INIT_KNOWN_FEATURES { \\\n%s\n}
 """ % (state.nr_entries,
+       state.common,
+       format_uint32s(state.known, 4),
        ))
 
     state.output.write(
-- 
2.1.4


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