[PATCH RFC 03/31] xen/x86: Store antifeatures inverted in a featureset

[Andrew Cooper <andrew.cooper3@citrix.com>]

Awkwardly, some new feature bits mean "Feature $X no longer works".
Store these inverted in a featureset.

This permits safe zero-extending of a smaller featureset as part of a
comparison, and safe reasoning (subset?, superset?, compatible? etc.)
without specific knowldge of meaning of each bit.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
---
 xen/arch/x86/Makefile                    |  1 +
 xen/arch/x86/cpu/common.c                |  3 +++
 xen/arch/x86/cpu/cpu.h                   |  2 ++
 xen/arch/x86/cpuid/Makefile              |  1 +
 xen/arch/x86/cpuid/cpuid-private.h       | 27 +++++++++++++++++++++++++++
 xen/arch/x86/cpuid/cpuid.c               | 16 ++++++++++++++++
 xen/include/asm-x86/cpufeature.h         |  2 +-
 xen/include/public/arch-x86/featureset.h |  7 ++++++-
 8 files changed, 57 insertions(+), 2 deletions(-)
 create mode 100644 xen/arch/x86/cpuid/Makefile
 create mode 100644 xen/arch/x86/cpuid/cpuid-private.h
 create mode 100644 xen/arch/x86/cpuid/cpuid.c

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 5f24951..122cbe9 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -1,5 +1,6 @@
 subdir-y += acpi
 subdir-y += cpu
+subdir-y += cpuid
 subdir-y += genapic
 subdir-y += hvm
 subdir-y += mm
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 87bd912..3496b13 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -323,6 +323,9 @@ void __cpuinit identify_cpu(struct cpuinfo_x86 *c)
 	 * The vendor-specific functions might have changed features.  Now
 	 * we do "generic changes."
 	 */
+	for (i = 0; i < XEN_NR_FEATURESET_ENTRIES; ++i) {
+		c->x86_capability[i] ^= inverted_features[i];
+	}
 
 	for (i = 0 ; i < NCAPINTS ; ++i)
 		c->x86_capability[i] &= ~cleared_caps[i];
diff --git a/xen/arch/x86/cpu/cpu.h b/xen/arch/x86/cpu/cpu.h
index 1877e7d..ca4048b 100644
--- a/xen/arch/x86/cpu/cpu.h
+++ b/xen/arch/x86/cpu/cpu.h
@@ -1,3 +1,5 @@
+#include "../cpuid/cpuid-private.h"
+
 /* attempt to consolidate cpu attributes */
 struct cpu_dev {
 	char	* c_vendor;
diff --git a/xen/arch/x86/cpuid/Makefile b/xen/arch/x86/cpuid/Makefile
new file mode 100644
index 0000000..3fb2e0b
--- /dev/null
+++ b/xen/arch/x86/cpuid/Makefile
@@ -0,0 +1 @@
+obj-y += cpuid.o
diff --git a/xen/arch/x86/cpuid/cpuid-private.h b/xen/arch/x86/cpuid/cpuid-private.h
new file mode 100644
index 0000000..c8b47b3
--- /dev/null
+++ b/xen/arch/x86/cpuid/cpuid-private.h
@@ -0,0 +1,27 @@
+#ifdef __XEN__
+
+#include <asm/cpufeature.h>
+
+#include <xen/lib.h>
+
+#else
+
+# error TODO for userspace
+
+#endif
+
+/*
+ * Bitmap of "anti" features which have their representation inverted when
+ * stored as a featureset.
+ */
+extern const uint32_t inverted_features[XEN_NR_FEATURESET_ENTRIES];
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/arch/x86/cpuid/cpuid.c b/xen/arch/x86/cpuid/cpuid.c
new file mode 100644
index 0000000..1578725
--- /dev/null
+++ b/xen/arch/x86/cpuid/cpuid.c
@@ -0,0 +1,16 @@
+#include "cpuid-private.h"
+
+const uint32_t inverted_features[XEN_NR_FEATURESET_ENTRIES] =
+{
+    [cpufeat_word(X86_FEATURE_FPU_SEL)] = cpufeat_mask(X86_FEATURE_FPU_SEL),
+};
+
+/*
+ * 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 87724a0..547ed7d 100644
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -81,7 +81,7 @@
 
 #define cpu_has_smep            boot_cpu_has(X86_FEATURE_SMEP)
 #define cpu_has_smap            boot_cpu_has(X86_FEATURE_SMAP)
-#define cpu_has_fpu_sel         (!boot_cpu_has(X86_FEATURE_NO_FPU_SEL))
+#define cpu_has_fpu_sel         boot_cpu_has(X86_FEATURE_FPU_SEL)
 
 #define cpu_has_ffxsr           ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) \
                                  && boot_cpu_has(X86_FEATURE_FFXSR))
diff --git a/xen/include/public/arch-x86/featureset.h b/xen/include/public/arch-x86/featureset.h
index 97e5c61..19abb98 100644
--- a/xen/include/public/arch-x86/featureset.h
+++ b/xen/include/public/arch-x86/featureset.h
@@ -35,6 +35,11 @@
  * contain any synthesied values.  New words may be added to the end of
  * featureset.
  *
+ * "Anti" features have their representation inverted.  This permits safe
+ * zero-extending of a smaller featureset as part of a comparison, and safe
+ * reasoning (subset?, superset?, compatible? etc.) without specific knowldge
+ * of meaning of each bit.
+ *
  * All featureset words currently originate from leaves specified for the
  * CPUID instruction, but this is not preclude other sources of information.
  */
@@ -173,7 +178,7 @@
 #define X86_FEATURE_INVPCID       ( 5*32+10) /* Invalidate Process Context ID */
 #define X86_FEATURE_RTM           ( 5*32+11) /* Restricted Transactional Memory */
 #define X86_FEATURE_CMT           ( 5*32+12) /* Cache Monitoring Technology */
-#define X86_FEATURE_NO_FPU_SEL    ( 5*32+13) /* FPU CS/DS stored as zero */
+#define X86_FEATURE_FPU_SEL       ( 5*32+13) /* ! FPU CS/DS stored as zero */
 #define X86_FEATURE_MPX           ( 5*32+14) /* Memory Protection Extensions */
 #define X86_FEATURE_CAT           ( 5*32+15) /* Cache Allocation Technology */
 #define X86_FEATURE_RDSEED        ( 5*32+18) /* RDSEED instruction */
-- 
2.1.4