target/i386: fix direction of "32-bit MMU" test

The low bit of MMU indices for x86 TCG indicates whether the processor is
in 32-bit mode and therefore linear addresses have to be masked to 32 bits.
However, the index was computed incorrectly, leading to possible conflicts
in the TLB for any address above 4G.

Analyzed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Fixes: b166180 ("target/i386: Fix physical address truncation", 2024-02-28)
Fixes: 1c15f97 ("target/i386: Fix physical address truncation" in stable-7.2)
Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2206
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 2cc6862)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(Mjt: move changes for x86_cpu_mmu_index() to cpu_mmu_index() due to missing
 v8.2.0-1030-gace0c5fe59 "target/i386: Populate CPUClass.mmu_index")

target/i386/cpu.h

@@ -2201,7 +2201,7 @@ uint64_t cpu_get_tsc(CPUX86State *env);
 
 static inline int cpu_mmu_index(CPUX86State *env, bool ifetch)
 {
-    int mmu_index_32 = (env->hflags & HF_CS64_MASK) ? 1 : 0;
+    int mmu_index_32 = (env->hflags & HF_CS64_MASK) ? 0 : 1;
     int mmu_index_base =
         (env->hflags & HF_CPL_MASK) == 3 ? MMU_USER64_IDX :
         !(env->hflags & HF_SMAP_MASK) ? MMU_KNOSMAP64_IDX :
@@ -2228,7 +2228,7 @@ static inline bool is_mmu_index_32(int mmu_index)
 
 static inline int cpu_mmu_index_kernel(CPUX86State *env)
 {
-    int mmu_index_32 = (env->hflags & HF_LMA_MASK) ? 1 : 0;
+    int mmu_index_32 = (env->hflags & HF_LMA_MASK) ? 0 : 1;
     int mmu_index_base =
         !(env->hflags & HF_SMAP_MASK) ? MMU_KNOSMAP64_IDX :
         ((env->hflags & HF_CPL_MASK) < 3 && (env->eflags & AC_MASK)) ? MMU_KNOSMAP64_IDX : MMU_KSMAP64_IDX;