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Subject[PATCH v8 2/5] x86/cpuid: Add generic table for cpuid dependencies
Date
From: Andi Kleen <ak@linux.intel.com>

Some CPUID features depend on other features. Currently it's
possible to to clear dependent features, but not clear the base features,
which can cause various interesting problems.

This patch implements a generic table to describe dependencies
between CPUID features, to be used by all code that clears
CPUID.

Some subsystems (like XSAVE) had an own implementation of this,
but it's better to do it all in a single place for everyone.

Then clear_cpu_cap and setup_clear_cpu_cap always look up
this table and clear all dependencies too.

This is intended to be a practical table: only for features
that make sense to clear. If someone for example clears FPU,
or other features that are essentially part of the required
base feature set, not much is going to work. Handling
that is right now out of scope. We're only handling
features which can be usefully cleared.

v2: Add EXPORT_SYMBOL for clear_cpu_cap for lguest
v3:
Fix handling of depending issues
Fix dups in the table (Jonathan McDowell)
v4:
Remove EXPORT_SYMBOL again as lguest is gone
Restructure dependencies as feature, dependency (Thomas Gleixner)
Move some code from header file to C file and turn macros into inlines (dito)
Simplify if conditions (dito)
Add missing dependency for AVX512F->AVX
Cc: Jonathan McDowell <noodles@earth.li>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
arch/x86/include/asm/cpufeature.h | 9 ++--
arch/x86/include/asm/cpufeatures.h | 5 ++
arch/x86/kernel/cpu/Makefile | 1 +
arch/x86/kernel/cpu/cpuid-deps.c | 107 +++++++++++++++++++++++++++++++++++++
4 files changed, 117 insertions(+), 5 deletions(-)
create mode 100644 arch/x86/kernel/cpu/cpuid-deps.c

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index d59c15c3defd..a0e13ac0c506 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -125,11 +125,10 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
#define boot_cpu_has(bit) cpu_has(&boot_cpu_data, bit)

#define set_cpu_cap(c, bit) set_bit(bit, (unsigned long *)((c)->x86_capability))
-#define clear_cpu_cap(c, bit) clear_bit(bit, (unsigned long *)((c)->x86_capability))
-#define setup_clear_cpu_cap(bit) do { \
- clear_cpu_cap(&boot_cpu_data, bit); \
- set_bit(bit, (unsigned long *)cpu_caps_cleared); \
-} while (0)
+
+extern void setup_clear_cpu_cap(unsigned bit);
+extern void clear_cpu_cap(struct cpuinfo_x86 *cinfo, unsigned bit);
+
#define setup_force_cpu_cap(bit) do { \
set_cpu_cap(&boot_cpu_data, bit); \
set_bit(bit, (unsigned long *)cpu_caps_set); \
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 2519c6c801c9..401a70992060 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -21,6 +21,11 @@
* this feature bit is not displayed in /proc/cpuinfo at all.
*/

+/*
+ * When adding new features here that depend on other features,
+ * please update the table in kernel/cpu/cpuid-deps.c
+ */
+
/* Intel-defined CPU features, CPUID level 0x00000001 (edx), word 0 */
#define X86_FEATURE_FPU ( 0*32+ 0) /* Onboard FPU */
#define X86_FEATURE_VME ( 0*32+ 1) /* Virtual Mode Extensions */
diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index e17942c131c8..de260fae1017 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -22,6 +22,7 @@ obj-y += rdrand.o
obj-y += match.o
obj-y += bugs.o
obj-$(CONFIG_CPU_FREQ) += aperfmperf.o
+obj-y += cpuid-deps.o

obj-$(CONFIG_PROC_FS) += proc.o
obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
new file mode 100644
index 000000000000..27be2fc9776d
--- /dev/null
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -0,0 +1,107 @@
+/* Declare dependencies between CPUIDs */
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <asm/cpufeature.h>
+
+struct cpuid_dep {
+ unsigned short feature;
+ unsigned short depends;
+};
+
+/*
+ * Table of CPUID features that depend on others.
+ *
+ * This only includes dependencies that can be usefully disabled, not
+ * features part of the base set (like FPU).
+ */
+const static struct cpuid_dep cpuid_deps[] = {
+ { X86_FEATURE_XSAVEOPT, X86_FEATURE_XSAVE },
+ { X86_FEATURE_XSAVEC, X86_FEATURE_XSAVE },
+ { X86_FEATURE_XSAVES, X86_FEATURE_XSAVE },
+ { X86_FEATURE_AVX, X86_FEATURE_XSAVE },
+ { X86_FEATURE_AVX512F, X86_FEATURE_XSAVE },
+ { X86_FEATURE_PKU, X86_FEATURE_XSAVE },
+ { X86_FEATURE_MPX, X86_FEATURE_XSAVE },
+ { X86_FEATURE_XGETBV1, X86_FEATURE_XSAVE },
+ { X86_FEATURE_XMM2, X86_FEATURE_XMM },
+ { X86_FEATURE_XMM3, X86_FEATURE_XMM2 },
+ { X86_FEATURE_XMM4_1, X86_FEATURE_XMM2 },
+ { X86_FEATURE_XMM4_2, X86_FEATURE_XMM2 },
+ { X86_FEATURE_XMM3, X86_FEATURE_XMM2 },
+ { X86_FEATURE_PCLMULQDQ, X86_FEATURE_XMM2 },
+ { X86_FEATURE_SSSE3, X86_FEATURE_XMM2, },
+ { X86_FEATURE_F16C, X86_FEATURE_XMM2, },
+ { X86_FEATURE_AES, X86_FEATURE_XMM2 },
+ { X86_FEATURE_FMA, X86_FEATURE_AVX },
+ { X86_FEATURE_AVX2, X86_FEATURE_AVX, },
+ { X86_FEATURE_AVX512F, X86_FEATURE_AVX, },
+ { X86_FEATURE_AVX512IFMA, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512PF, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512ER, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512CD, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512DQ, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512BW, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512VL, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512VBMI, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512_4VNNIW, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512_4FMAPS, X86_FEATURE_AVX512F },
+ { X86_FEATURE_AVX512_VPOPCNTDQ, X86_FEATURE_AVX512F },
+ {}
+};
+
+static inline void __clear_cpu_cap(struct cpuinfo_x86 *cinfo, unsigned bit)
+{
+ clear_bit(bit, (unsigned long *)(cinfo->x86_capability));
+}
+
+static inline void __setup_clear_cpu_cap(unsigned bit)
+{
+ clear_cpu_cap(&boot_cpu_data, bit);
+ set_bit(bit, (unsigned long *)cpu_caps_cleared);
+}
+
+static inline void clear_feature(struct cpuinfo_x86 *cinfo, unsigned feat)
+{
+ if (!cinfo)
+ __setup_clear_cpu_cap(feat);
+ else
+ __clear_cpu_cap(cinfo, feat);
+}
+
+static void do_clear_cpu_cap(struct cpuinfo_x86 *cinfo, unsigned feat)
+{
+ bool changed;
+ __u32 disable[NCAPINTS + NBUGINTS];
+ unsigned long *disable_mask = (unsigned long *)disable;
+ const struct cpuid_dep *d;
+
+ clear_feature(cinfo, feat);
+
+ /* Collect all features to disable, handling dependencies */
+ memset(disable, 0, sizeof(disable));
+ __set_bit(feat, disable_mask);
+ /* Loop until we get a stable state. */
+ do {
+ changed = false;
+ for (d = cpuid_deps; d->feature; d++) {
+ if (!test_bit(d->depends, disable_mask))
+ continue;
+ if (__test_and_set_bit(d->feature, disable_mask))
+ continue;
+
+ changed = true;
+ clear_feature(cinfo, d->feature);
+ }
+ } while (changed);
+}
+
+void clear_cpu_cap(struct cpuinfo_x86 *cinfo, unsigned feat)
+{
+ do_clear_cpu_cap(cinfo, feat);
+}
+
+void setup_clear_cpu_cap(unsigned feat)
+{
+ do_clear_cpu_cap(NULL, feat);
+}
--
2.13.6
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