Merged PR 8129085: Disable AVX2 in Windows boot lib for AMD64

We're investigating boot failures in the lab (see bugs #42178021, #42182776) but so far we've made limited progress because the boot debugger unexpectedly disconnects, and we haven't been able to reproduce the issue locally. Our working theory is that recent SHA2 optimizations may have increased code size and/or stack usage beyond what the boot environment can accommodate. To confirm or exclude this diagnosis, this change disables AVX2 for AMD64 in the boot environment, which will remove the new SHA2 optimizations.

Related work items: #42178021, #42182776

Author: mlindgren

lib/env_windowsBootLib.c

@@ -30,18 +30,14 @@ BlStatusError (
 
 SYMCRYPT_CPU_FEATURES SYMCRYPT_CALL SymCryptCpuFeaturesNeverPresentEnvWindowsBootlibrary()
 {
-#if SYMCRYPT_CPU_X86 
+#if SYMCRYPT_CPU_X86 | SYMCRYPT_CPU_AMD64
     //
-    // We disable AVX2 for X86.
+    // We disable AVX2 for X86 (including X86-64)
     // This reduces codesize for bootmgr on PCAT which is codesize-constrained,
     // and is simpler than creating a separate PCAT-bootlib SymCrypt environment.
-    // We expect that very few AVX2-capable machines will boot x86, and x86 still has XMM-based parallel
-    // hashing, so the performance loss is quite small.
-    // We considered locking out AES-NI as well; that would reduce codesize, but slow down BitLocker boot on
-    // x86 which is an important mobile scenario.
     //
     return SYMCRYPT_CPU_FEATURE_AVX2;
-#elif SYMCRYPT_CPU_ARM | SYMCRYPT_CPU_ARM64 | SYMCRYPT_CPU_AMD64
+#elif SYMCRYPT_CPU_ARM | SYMCRYPT_CPU_ARM64
     return 0;
 #endif
 }