[PATCH v2 2/2] [RfC] expose host-phys-bits to guest

[Gerd Hoffmann <kraxel@xxxxxxxxxx>]

Move "host-phys-bits" property from cpu->host_phys_bits to
cpu->env.features[FEAT_KVM_HINTS] (KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID bit).

This has the effect that the guest can see whenever host-phys-bits
is turned on or not and act accordingly.

Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
---
 target/i386/cpu.h      | 3 ---
 hw/i386/microvm.c      | 7 ++++++-
 target/i386/cpu.c      | 3 +--
 target/i386/host-cpu.c | 5 ++++-
 target/i386/kvm/kvm.c  | 1 +
 5 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 82004b65b944..b9c6d3d9cac6 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1898,9 +1898,6 @@ struct ArchCPU {
     /* if true fill the top bits of the MTRR_PHYSMASKn variable range */
     bool fill_mtrr_mask;
 
-    /* if true override the phys_bits value with a value read from the host */
-    bool host_phys_bits;
-
     /* if set, limit maximum value for phys_bits when host_phys_bits is true */
     uint8_t host_phys_bits_limit;
 
diff --git a/hw/i386/microvm.c b/hw/i386/microvm.c
index 52cafa003d8a..316bbc8ef946 100644
--- a/hw/i386/microvm.c
+++ b/hw/i386/microvm.c
@@ -54,6 +54,8 @@
 #include "kvm/kvm_i386.h"
 #include "hw/xen/start_info.h"
 
+#include "standard-headers/asm-x86/kvm_para.h"
+
 #define MICROVM_QBOOT_FILENAME "qboot.rom"
 #define MICROVM_BIOS_FILENAME  "bios-microvm.bin"
 
@@ -424,7 +426,10 @@ static void microvm_device_pre_plug_cb(HotplugHandler *hotplug_dev,
 {
     X86CPU *cpu = X86_CPU(dev);
 
-    cpu->host_phys_bits = true; /* need reliable phys-bits */
+    /* need reliable phys-bits */
+    cpu->env.features[FEAT_KVM_HINTS] |=
+        (1 << KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID);
+
     x86_cpu_pre_plug(hotplug_dev, dev, errp);
 }
 
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 1db1278a599b..d60f4498a3c3 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -778,7 +778,7 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
     [FEAT_KVM_HINTS] = {
         .type = CPUID_FEATURE_WORD,
         .feat_names = {
-            "kvm-hint-dedicated", NULL, NULL, NULL,
+            "kvm-hint-dedicated", "host-phys-bits", NULL, NULL,
             NULL, NULL, NULL, NULL,
             NULL, NULL, NULL, NULL,
             NULL, NULL, NULL, NULL,
@@ -7016,7 +7016,6 @@ 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_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),
     DEFINE_PROP_UINT32("level-func7", X86CPU, env.cpuid_level_func7,
diff --git a/target/i386/host-cpu.c b/target/i386/host-cpu.c
index 10f8aba86e53..a1d6b3ac962e 100644
--- a/target/i386/host-cpu.c
+++ b/target/i386/host-cpu.c
@@ -13,6 +13,8 @@
 #include "qapi/error.h"
 #include "sysemu/sysemu.h"
 
+#include "standard-headers/asm-x86/kvm_para.h"
+
 /* Note: Only safe for use on x86(-64) hosts */
 static uint32_t host_cpu_phys_bits(void)
 {
@@ -68,7 +70,8 @@ static uint32_t host_cpu_adjust_phys_bits(X86CPU *cpu)
         warned = true;
     }
 
-    if (cpu->host_phys_bits) {
+    if (cpu->env.features[FEAT_KVM_HINTS] &
+        (1 << KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID)) {
         /* The user asked for us to use the host physical bits */
         phys_bits = host_phys_bits;
         if (cpu->host_phys_bits_limit &&
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index a1fd1f53791d..3335c57b21b2 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -459,6 +459,7 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
         }
     } else if (function == KVM_CPUID_FEATURES && reg == R_EDX) {
         ret |= 1U << KVM_HINTS_REALTIME;
+        ret |= 1U << KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID;
     }
 
     return ret;
-- 
2.37.3