A lot of FPU using driver code is querying complex CPU features to be
able to figure out whether a given set of xstate features is supported
by the CPU or not.
Introduce a simplified API function that can be used on any CPU type
to get this information. Also add an error string return pointer,
so that the driver can print a meaningful error message with a
standardized feature name.
Also mark xfeatures_mask as __read_only.
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Dave Hansen <dave.han...@linux.intel.com>
Cc: Fenghua Yu <fenghua...@intel.com>
Cc: H. Peter Anvin <h...@zytor.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
arch/x86/include/asm/fpu/api.h | 9 +++++++++
arch/x86/kernel/fpu/xstate.c | 53
++++++++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 61 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index 62035cc1d961..1429a7c736db 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -36,4 +36,13 @@ extern bool irq_fpu_usable(void);
extern int irq_ts_save(void);
extern void irq_ts_restore(int TS_state);
+/*
+ * Query the presence of one or more xfeatures. Works on any legacy CPU as
well.
+ *
+ * If 'feature_name' is set then put a human-readable description of
+ * the feature there as well - this can be used to print error (or success)
+ * messages.
+ */
+extern int cpu_has_xfeatures(u64 xfeatures_mask, const char **feature_name);
+
#endif /* _ASM_X86_FPU_API_H */
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index f549e2a44336..2e52f01f4931 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -11,10 +11,23 @@
#include <asm/tlbflush.h>
#include <asm/xcr.h>
+static const char *xfeature_names[] =
+{
+ "x87 floating point registers" ,
+ "SSE registers" ,
+ "AVX registers" ,
+ "MPX bounds registers" ,
+ "MPX CSR" ,
+ "AVX-512 opmask" ,
+ "AVX-512 Hi256" ,
+ "AVX-512 ZMM_Hi256" ,
+ "unknown xstate feature" ,
+};
+
/*
* Mask of xstate features supported by the CPU and the kernel:
*/
-u64 xfeatures_mask;
+u64 xfeatures_mask __read_mostly;
/*
* Represents init state for the supported extended state.
@@ -29,6 +42,44 @@ static unsigned int
xstate_comp_offsets[sizeof(xfeatures_mask)*8];
static unsigned int xfeatures_nr;
/*
+ * Return whether the system supports a given xfeature.
+ *
+ * Also return the name of the (most advanced) feature that the caller
requested:
+ */
+int cpu_has_xfeatures(u64 xfeatures_needed, const char **feature_name)
+{
+ u64 xfeatures_missing = xfeatures_needed & ~xfeatures_mask;
+
+ if (unlikely(feature_name)) {
+ long xfeature_idx, max_idx;
+ u64 xfeatures_print;
+ /*
+ * So we use FLS here to be able to print the most advanced
+ * feature that was requested but is missing. So if a driver
+ * asks about "XSTATE_SSE | XSTATE_YMM" we'll print the
+ * missing AVX feature - this is the most informative message
+ * to users:
+ */
+ if (xfeatures_missing)
+ xfeatures_print = xfeatures_missing;
+ else
+ xfeatures_print = xfeatures_needed;
+
+ xfeature_idx = fls64(xfeatures_print)-1;
+ max_idx = ARRAY_SIZE(xfeature_names)-1;
+ xfeature_idx = min(xfeature_idx, max_idx);
+
+ *feature_name = xfeature_names[xfeature_idx];
+ }
+
+ if (xfeatures_missing)
+ return 0;
+
+ return 1;
+}
+EXPORT_SYMBOL_GPL(cpu_has_xfeatures);
+
+/*
* When executing XSAVEOPT (optimized XSAVE), if a processor implementation
* detects that an FPU state component is still (or is again) in its
* initialized state, it may clear the corresponding bit in the
header.xfeatures
--
2.1.0
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