target/i386: add guest-phys-bits cpu property

Allows to set guest-phys-bits (cpuid leaf 80000008, eax[23:16])
via -cpu $model,guest-phys-bits=$nr.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-ID: <20240318155336.156197-3-kraxel@redhat.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/pc.c

@@ -78,7 +78,9 @@
     { "qemu64-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, },\
     { "athlon-" TYPE_X86_CPU, "model-id", "QEMU Virtual CPU version " v, },
 
-GlobalProperty pc_compat_9_0[] = {};
+GlobalProperty pc_compat_9_0[] = {
+    { TYPE_X86_CPU, "guest-phys-bits", "0" },
+};
 const size_t pc_compat_9_0_len = G_N_ELEMENTS(pc_compat_9_0);
 
 GlobalProperty pc_compat_8_2[] = {};

target/i386/cpu.c

@@ -6570,6 +6570,7 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         if (env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) {
             /* 64 bit processor */
              *eax |= (cpu_x86_virtual_addr_width(env) << 8);
+             *eax |= (cpu->guest_phys_bits << 16);
         }
         *ebx = env->features[FEAT_8000_0008_EBX];
         if (cs->nr_cores * cs->nr_threads > 1) {
@@ -7329,6 +7330,14 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
         goto out;
     }
 
+    if (cpu->guest_phys_bits == -1) {
+        /*
+         * If it was not set by the user, or by the accelerator via
+         * cpu_exec_realizefn, clear.
+         */
+        cpu->guest_phys_bits = 0;
+    }
+
     if (cpu->ucode_rev == 0) {
         /*
          * The default is the same as KVM's. Note that this check
@@ -7379,6 +7388,14 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
         if (cpu->phys_bits == 0) {
             cpu->phys_bits = TCG_PHYS_ADDR_BITS;
         }
+        if (cpu->guest_phys_bits &&
+            (cpu->guest_phys_bits > cpu->phys_bits ||
+            cpu->guest_phys_bits < 32)) {
+            error_setg(errp, "guest-phys-bits should be between 32 and %u "
+                             " (but is %u)",
+                             cpu->phys_bits, cpu->guest_phys_bits);
+            return;
+        }
     } else {
         /* For 32 bit systems don't use the user set value, but keep
          * phys_bits consistent with what we tell the guest.
@@ -7387,6 +7404,10 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
             error_setg(errp, "phys-bits is not user-configurable in 32 bit");
             return;
         }
+        if (cpu->guest_phys_bits != 0) {
+            error_setg(errp, "guest-phys-bits is not user-configurable in 32 bit");
+            return;
+        }
 
         if (env->features[FEAT_1_EDX] & (CPUID_PSE36 | CPUID_PAE)) {
             cpu->phys_bits = 36;
@@ -7887,6 +7908,7 @@ static Property x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("x-force-features", X86CPU, force_features, false),
     DEFINE_PROP_BOOL("kvm", X86CPU, expose_kvm, true),
     DEFINE_PROP_UINT32("phys-bits", X86CPU, phys_bits, 0),
+    DEFINE_PROP_UINT32("guest-phys-bits", X86CPU, guest_phys_bits, -1),
     DEFINE_PROP_BOOL("host-phys-bits", X86CPU, host_phys_bits, false),
     DEFINE_PROP_UINT8("host-phys-bits-limit", X86CPU, host_phys_bits_limit, 0),
     DEFINE_PROP_BOOL("fill-mtrr-mask", X86CPU, fill_mtrr_mask, true),

target/i386/cpu.h

@@ -2027,6 +2027,14 @@ struct ArchCPU {
     /* Number of physical address bits supported */
     uint32_t phys_bits;
 
+    /*
+     * Number of guest physical address bits available. Usually this is
+     * identical to host physical address bits. With NPT or EPT 4-level
+     * paging, guest physical address space might be restricted to 48 bits
+     * even if the host cpu supports more physical address bits.
+     */
+    uint32_t guest_phys_bits;
+
     /* in order to simplify APIC support, we leave this pointer to the
        user */
     struct DeviceState *apic_state;