[Xen-devel] [PATCH 3/4] x86: don't use FPU instructions when there is no FPU

["Jan Beulich" <JBeulich@xxxxxxxx>]

One of the many things we need to do if we want to eventually be able
to run on e.g. Xeon Phi.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -261,6 +261,9 @@ static void __cpuinit generic_identify(s
                cpuid_count(0x00000007, 0, &dummy, &ebx, &dummy, &dummy);
                c->x86_capability[X86_FEATURE_FSGSBASE / 32] = ebx;
        }
+
+       if ( !cpu_has_fpu )
+               __set_bit(X86_FEATURE_NO_FPU_SEL, c->x86_capability);
 }
 
 /*
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -21,7 +21,8 @@ static void fpu_init(void)
 {
     uint32_t val = MXCSR_DEFAULT;
     
-    asm volatile ( "fninit" );
+    if ( cpu_has_fpu || cpu_has_mmx )
+        asm volatile ( "fninit" );
 
     /* load default value into MXCSR control/status register */
     asm volatile ( "ldmxcsr %0" : : "m" (val) );
@@ -59,7 +60,7 @@ static inline void fpu_fxrstor(struct vc
      * sometimes new user value. Both should be ok. Use the FPU saved
      * data block as a safe address because it should be in L1.
      */
-    if ( !(fpu_ctxt->fsw & 0x0080) &&
+    if ( cpu_has_fpu && !(fpu_ctxt->fsw & 0x0080) &&
          boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
     {
         asm volatile ( "fnclex\n\t"
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -170,6 +170,7 @@
 #define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1
 #define CPUID5_ECX_INTERRUPT_BREAK      0x2
 
+#define cpu_has_fpu            boot_cpu_has(X86_FEATURE_FPU)
 #define cpu_has_de             1
 #define cpu_has_pse            1
 #define cpu_has_pge            1
@@ -177,7 +178,7 @@
 #define cpu_has_apic           boot_cpu_has(X86_FEATURE_APIC)
 #define cpu_has_sep            boot_cpu_has(X86_FEATURE_SEP)
 #define cpu_has_mtrr           1
-#define cpu_has_mmx            1
+#define cpu_has_mmx            boot_cpu_has(X86_FEATURE_MMX)
 #define cpu_has_xmm3           boot_cpu_has(X86_FEATURE_XMM3)
 #define cpu_has_ht             boot_cpu_has(X86_FEATURE_HT)
 #define cpu_has_mp             1

Attachment: x86-check-FPU-MMX.patch
Description: Text document

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