[PATCH 4.14 018/159] x86/fpu: Make XSAVE check the base CPUID features before enabling

Greg Kroah-Hartman
2017-12-22T10:00:46Z

From: Andi Kleen <ak@linux.intel.com>

commit ccb18db2ab9d923df07e7495123fe5fb02329713 upstream.

Before enabling XSAVE, not only check the XSAVE specific CPUID bits,
but also the base CPUID features of the respective XSAVE feature.
This allows to disable individual XSAVE states using the existing
clearcpuid= option, which can be useful for performance testing
and debugging, and also in general avoids inconsistencies.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20171013215645.23166-5-andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kernel/fpu/xstate.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -15,6 +15,7 @@
#include <asm/fpu/xstate.h>

#include <asm/tlbflush.h>
+#include <asm/cpufeature.h>

/*
* Although we spell it out in here, the Processor Trace
@@ -36,6 +37,19 @@ static const char *xfeature_names[] =
"unknown xstate feature" ,
};

+static short xsave_cpuid_features[] __initdata = {
+ X86_FEATURE_FPU,
+ X86_FEATURE_XMM,
+ X86_FEATURE_AVX,
+ X86_FEATURE_MPX,
+ X86_FEATURE_MPX,
+ X86_FEATURE_AVX512F,
+ X86_FEATURE_AVX512F,
+ X86_FEATURE_AVX512F,
+ X86_FEATURE_INTEL_PT,
+ X86_FEATURE_PKU,
+};
+
/*
* Mask of xstate features supported by the CPU and the kernel:
*/
@@ -726,6 +740,7 @@ void __init fpu__init_system_xstate(void
unsigned int eax, ebx, ecx, edx;
static int on_boot_cpu __initdata = 1;
int err;
+ int i;

WARN_ON_FPU(!on_boot_cpu);
on_boot_cpu = 0;
@@ -759,6 +774,14 @@ void __init fpu__init_system_xstate(void
goto out_disable;
}

+ /*
+ * Clear XSAVE features that are disabled in the normal CPUID.
+ */
+ for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) {
+ if (!boot_cpu_has(xsave_cpuid_features[i]))
+ xfeatures_mask &= ~BIT(i);
+ }
+
xfeatures_mask &= fpu__get_supported_xfeatures_mask();

/* Enable xstate instructions to be able to continue with initialization: */