Misc x86 fixes:

- Fix the boot-time memcmp() asm implementation's constraints
    and optimization properties (Mauricio Faria de Oliveira)
 
  - Move the 0xd0...0xd7 AMD Zen5 model range from the Zen6
    range where it mistakenly ended up (Pratik Vishwakarma)
 
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'x86-urgent-2026-08-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull misc x86 fixes from Ingo Molnar:

 - Fix the boot-time memcmp() asm implementation's constraints
   and optimization properties (Mauricio Faria de Oliveira)

 - Move the 0xd0...0xd7 AMD Zen5 model range from the Zen6
   range where it mistakenly ended up (Pratik Vishwakarma)

* tag 'x86-urgent-2026-08-02' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/CPU/AMD: Carve out a Zen5 models range
  x86/boot: Add volatile, clobbers and zero-length test in memcmp()

arch/x86/boot/string.c

@@ -32,8 +32,15 @@
 int memcmp(const void *s1, const void *s2, size_t len)
 {
 	bool diff;
-	asm("repe cmpsb"
-	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
+
+	/*
+	 * Make sure ZF is properly set in the len==0 case because in it,
+	 * RCX==0 and the REPE; CMPSB won't get executed.
+	 */
+	asm volatile("test %3, %3\n\t"
+		     "repe cmpsb"
+		     : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len)
+		     : : "cc", "memory");
 	return diff;
 }
 

arch/x86/kernel/cpu/amd.c

@@ -515,11 +515,13 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
 		case 0x00 ... 0x2f:
 		case 0x40 ... 0x4f:
 		case 0x60 ... 0x7f:
+		case 0xd0 ... 0xd7:
 			setup_force_cpu_cap(X86_FEATURE_ZEN5);
 			break;
 		case 0x50 ... 0x5f:
 		case 0x80 ... 0xaf:
-		case 0xc0 ... 0xef:
+		case 0xc0 ... 0xcf:
+		case 0xd8 ... 0xef:
 			setup_force_cpu_cap(X86_FEATURE_ZEN6);
 			break;
 		default: