Add option to change SVE vector length for current and children processes

src/coreclr/vm/arm64/asmhelpers.S

@@ -23,6 +23,13 @@ LEAF_ENTRY GetDataCacheZeroIDReg, _TEXT
     ret     lr
 LEAF_END GetDataCacheZeroIDReg, _TEXT
 
+// uint64_t GetSveLengthFromOS(void);
+.arch_extension sve
+    LEAF_ENTRY GetSveLengthFromOS, _TEXT
+        rdvl    x0, 1
+        ret     lr
+    LEAF_END GetSveLengthFromOS, _TEXT
+
 //-----------------------------------------------------------------------------
 // This routine captures the machine state. It is used by helper method frame
 //-----------------------------------------------------------------------------

src/coreclr/vm/arm64/asmhelpers.asm

@@ -78,6 +78,12 @@
         ret     lr
     LEAF_END
 
+;; uint64_t GetSveLengthFromOS(void);
+    LEAF_ENTRY GetSveLengthFromOS
+        rdvl    x0, 1
+        ret     lr
+    LEAF_END
+
 ;;-----------------------------------------------------------------------------
 ;; This routine captures the machine state. It is used by helper method frame
 ;;-----------------------------------------------------------------------------

src/coreclr/vm/codeman.cpp

@@ -1257,12 +1257,12 @@ void EEJitManager::SetCpuInfo()
 
     int cpuFeatures = minipal_getcpufeatures();
 
-#if defined(TARGET_X86) || defined(TARGET_AMD64)
-    CPUCompileFlags.Set(InstructionSet_VectorT128);
-
     // Get the maximum bitwidth of Vector<T>, rounding down to the nearest multiple of 128-bits
     uint32_t maxVectorTBitWidth = (CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_MaxVectorTBitWidth) / 128) * 128;
 
+#if defined(TARGET_X86) || defined(TARGET_AMD64)
+    CPUCompileFlags.Set(InstructionSet_VectorT128);
+
     if (((cpuFeatures & XArchIntrinsicConstants_Avx2) != 0) && ((maxVectorTBitWidth == 0) || (maxVectorTBitWidth >= 256)))
     {
         // We allow 256-bit Vector<T> by default
@@ -1514,7 +1514,14 @@ void EEJitManager::SetCpuInfo()
 
     if (((cpuFeatures & ARM64IntrinsicConstants_Sve) != 0) && CLRConfig::GetConfigValue(CLRConfig::EXTERNAL_EnableArm64Sve))
     {
-        CPUCompileFlags.Set(InstructionSet_Sve);
+        uint32_t maxVectorTLength = (maxVectorTBitWidth / 8);
+        uint64_t sveLengthFromOS = GetSveLengthFromOS();
+
+        // Do not enable SVE when the user specified vector length is smaller than the one offered by underlying OS.
+        if ((maxVectorTLength >= sveLengthFromOS) || (maxVectorTBitWidth == 0))
+        {
+            CPUCompileFlags.Set(InstructionSet_Sve);
+        }
     }
 
     // DCZID_EL0<4> (DZP) indicates whether use of DC ZVA instructions is permitted (0) or prohibited (1).

src/coreclr/vm/codeman.h

@@ -69,6 +69,10 @@ Module Name:
 #include "gcinfo.h"
 #include "eexcp.h"
 
+#if defined(TARGET_ARM64)
+extern "C" uint64_t GetSveLengthFromOS();
+#endif
+
 class MethodDesc;
 class ICorJitCompiler;
 class IJitManager;