x86: cpu: make sure number of addressable IDs for processor cores meets the spec

Accourding Intel's CPUID[EAX=04H] resulting bits 31 - 26 in EAX
should be:
"
 **** The nearest power-of-2 integer that is not smaller than (1 + EAX[31:26]) is the number of unique
    Core_IDs reserved for addressing different processor cores in a physical package. Core ID is a subset of
    bits of the initial APIC ID.
"

ensure that values stored in EAX[31-26] always meets this condition.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20220524151020.2541698-2-imammedo@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 9fdfec9d8bcc9b3845ead0c6a902995ddd4168de..94cc4a8700dee487895f3e626a5c0c0626646e1f 100644 (file)
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5287,7 +5287,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
             /* QEMU gives out its own APIC IDs, never pass down bits 31..26.  */
             *eax &= ~0xFC000000;
             if ((*eax & 31) && cs->nr_cores > 1) {
-                *eax |= (cs->nr_cores - 1) << 26;
+                *eax |= (pow2ceil(cs->nr_cores) - 1) << 26;
             }
         } else if (cpu->vendor_cpuid_only && IS_AMD_CPU(env)) {
             *eax = *ebx = *ecx = *edx = 0;