[PATCH v7 19/24] whpx: arm64: implement -cpu host

Mohamed Mediouni
2025-10-16T16:57:34Z

Logic to fetch MIDR_EL1 for cpu 0 adapted from:
https://github.com/FEX-Emu/FEX/blob/e6de17e72ef03aa88ba14fa0ec13163061608c74/Source/Windows/Common/CPUFeatures.cpp#L62

Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>
---
hw/arm/virt.c | 2 +-
target/arm/cpu64.c | 19 ++++---
target/arm/whpx/whpx-all.c | 104 +++++++++++++++++++++++++++++++++++++
target/arm/whpx_arm.h | 1 +
4 files changed, 119 insertions(+), 7 deletions(-)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index d3dd36908a..1904765db3 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -3312,7 +3312,7 @@ static void virt_machine_class_init(ObjectClass *oc, const void *data)
#ifdef TARGET_AARCH64
ARM_CPU_TYPE_NAME("cortex-a53"),
ARM_CPU_TYPE_NAME("cortex-a57"),
-#if defined(CONFIG_KVM) || defined(CONFIG_HVF)
+#if defined(CONFIG_KVM) || defined(CONFIG_HVF) || defined(CONFIG_WHPX)
ARM_CPU_TYPE_NAME("host"),
#endif /* CONFIG_KVM || CONFIG_HVF */
#endif /* TARGET_AARCH64 */
diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 26cf7e6dfa..3f00071081 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -26,10 +26,13 @@
#include "qemu/units.h"
#include "system/kvm.h"
#include "system/hvf.h"
+#include "system/whpx.h"
+#include "system/hw_accel.h"
#include "system/qtest.h"
#include "system/tcg.h"
#include "kvm_arm.h"
#include "hvf_arm.h"
+#include "whpx_arm.h"
#include "qapi/visitor.h"
#include "hw/qdev-properties.h"
#include "internals.h"
@@ -522,7 +525,7 @@ void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp)
isar2 = FIELD_DP64(isar2, ID_AA64ISAR2, APA3, 0);
isar2 = FIELD_DP64(isar2, ID_AA64ISAR2, GPA3, 0);

- if (kvm_enabled() || hvf_enabled()) {
+ if (hwaccel_enabled()) {
/*
* Exit early if PAuth is enabled and fall through to disable it.
* The algorithm selection properties are not present.
@@ -599,10 +602,10 @@ void aarch64_add_pauth_properties(Object *obj)

/* Default to PAUTH on, with the architected algorithm on TCG. */
qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_property);
- if (kvm_enabled() || hvf_enabled()) {
+ if (hwaccel_enabled()) {
/*
* Mirror PAuth support from the probed sysregs back into the
- * property for KVM or hvf. Is it just a bit backward? Yes it is!
+ * property for HW accel. Is it just a bit backward? Yes it is!
* Note that prop_pauth is true whether the host CPU supports the
* architected QARMA5 algorithm or the IMPDEF one. We don't
* provide the separate pauth-impdef property for KVM or hvf,
@@ -773,6 +776,10 @@ static void aarch64_host_initfn(Object *obj)
ARMCPU *cpu = ARM_CPU(obj);
hvf_arm_set_cpu_features_from_host(cpu);
aarch64_add_pauth_properties(obj);
+#elif defined(CONFIG_WHPX)
+ ARMCPU *cpu = ARM_CPU(obj);
+ whpx_arm_set_cpu_features_from_host(cpu);
+ aarch64_add_pauth_properties(obj);
#else
g_assert_not_reached();
#endif
@@ -780,8 +787,8 @@ static void aarch64_host_initfn(Object *obj)

static void aarch64_max_initfn(Object *obj)
{
- if (kvm_enabled() || hvf_enabled()) {
- /* With KVM or HVF, '-cpu max' is identical to '-cpu host' */
+ if (hwaccel_enabled()) {
+ /* When hardware acceleration enabled, '-cpu max' is identical to '-cpu host' */
aarch64_host_initfn(obj);
return;
}
@@ -800,7 +807,7 @@ static const ARMCPUInfo aarch64_cpus[] = {
{ .name = "cortex-a57", .initfn = aarch64_a57_initfn },
{ .name = "cortex-a53", .initfn = aarch64_a53_initfn },
{ .name = "max", .initfn = aarch64_max_initfn },
-#if defined(CONFIG_KVM) || defined(CONFIG_HVF)
+#if defined(CONFIG_KVM) || defined(CONFIG_HVF) || defined(CONFIG_WHPX)
{ .name = "host", .initfn = aarch64_host_initfn },
#endif
};
diff --git a/target/arm/whpx/whpx-all.c b/target/arm/whpx/whpx-all.c
index 19513b50a3..680954f4b5 100644
--- a/target/arm/whpx/whpx-all.c
+++ b/target/arm/whpx/whpx-all.c
@@ -41,6 +41,17 @@

#include <winhvplatform.h>
#include <winhvplatformdefs.h>
+#include <winreg.h>
+
+typedef struct ARMHostCPUFeatures {
+ ARMISARegisters isar;
+ uint64_t features;
+ uint64_t midr;
+ uint32_t reset_sctlr;
+ const char *dtb_compatible;
+} ARMHostCPUFeatures;
+
+static ARMHostCPUFeatures arm_host_cpu_features;

struct whpx_reg_match {
WHV_REGISTER_NAME reg;
@@ -695,6 +706,99 @@ static void clamp_id_aa64mmfr0_parange_to_ipa_size(ARMISARegisters *isar)
SET_IDREG(isar, ID_AA64MMFR0, id_aa64mmfr0);
}

+static uint64_t whpx_read_midr(void)
+{
+ HKEY key;
+ uint64_t midr_el1;
+ DWORD size = sizeof(midr_el1);
+ const char *path = "Hardware\\Description\\System\\CentralProcessor\\0\\";
+ assert(!RegOpenKeyExA(HKEY_LOCAL_MACHINE, path, 0, KEY_READ, &key));
+ assert(!RegGetValueA(key, NULL, "CP 4000", RRF_RT_REG_QWORD, NULL, &midr_el1, &size));
+ RegCloseKey(key);
+ return midr_el1;
+}
+
+static bool whpx_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
+{
+ const struct isar_regs {
+ WHV_REGISTER_NAME reg;
+ uint64_t *val;
+ } regs[] = {
+ { WHvArm64RegisterIdAa64Pfr0El1, &ahcf->isar.idregs[ID_AA64PFR0_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Pfr1El1, &ahcf->isar.idregs[ID_AA64PFR1_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Dfr0El1, &ahcf->isar.idregs[ID_AA64DFR0_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Dfr1El1 , &ahcf->isar.idregs[ID_AA64DFR1_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Isar0El1, &ahcf->isar.idregs[ID_AA64ISAR0_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Isar1El1, &ahcf->isar.idregs[ID_AA64ISAR1_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Isar2El1, &ahcf->isar.idregs[ID_AA64ISAR2_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Mmfr0El1, &ahcf->isar.idregs[ID_AA64MMFR0_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Mmfr1El1, &ahcf->isar.idregs[ID_AA64MMFR1_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Mmfr2El1, &ahcf->isar.idregs[ID_AA64MMFR2_EL1_IDX] },
+ { WHvArm64RegisterIdAa64Mmfr3El1, &ahcf->isar.idregs[ID_AA64MMFR2_EL1_IDX] }
+ };
+
+ int i;
+ WHV_REGISTER_VALUE val;
+
+ ahcf->dtb_compatible = "arm,armv8";
+ ahcf->features = (1ULL << ARM_FEATURE_V8) |
+ (1ULL << ARM_FEATURE_NEON) |
+ (1ULL << ARM_FEATURE_AARCH64) |
+ (1ULL << ARM_FEATURE_PMU) |
+ (1ULL << ARM_FEATURE_GENERIC_TIMER);
+
+ for (i = 0; i < ARRAY_SIZE(regs); i++) {
+ clean_whv_register_value(&val);
+ whpx_get_global_reg(regs[i].reg, &val);
+ *regs[i].val = val.Reg64;
+ }
+
+ /*
+ * MIDR_EL1 is not a global register on WHPX
+ * As such, read the CPU0 from the registry to get a consistent value.
+ * Otherwise, on heterogenous systems, you'll get variance between CPUs.
+ */
+ ahcf->midr = whpx_read_midr();
+
+ clamp_id_aa64mmfr0_parange_to_ipa_size(&ahcf->isar);
+
+ /*
+ * Disable SVE, which is not supported by QEMU whpx yet.
+ * Work needed for SVE support:
+ * - SVE state save/restore
+ * - any potentially needed VL management
+ * Also disable SME at the same time. (not currently supported by Hyper-V)
+ */
+ SET_IDREG(&ahcf->isar, ID_AA64PFR0,
+ GET_IDREG(&ahcf->isar, ID_AA64PFR0) & ~R_ID_AA64PFR0_SVE_MASK);
+
+ SET_IDREG(&ahcf->isar, ID_AA64PFR1,
+ GET_IDREG(&ahcf->isar, ID_AA64PFR1) & ~R_ID_AA64PFR1_SME_MASK);
+
+ return true;
+}
+
+void whpx_arm_set_cpu_features_from_host(ARMCPU *cpu)
+{
+ if (!arm_host_cpu_features.dtb_compatible) {
+ if (!whpx_enabled() ||
+ !whpx_arm_get_host_cpu_features(&arm_host_cpu_features)) {
+ /*
+ * We can't report this error yet, so flag that we need to
+ * in arm_cpu_realizefn().
+ */
+ cpu->host_cpu_probe_failed = true;
+ return;
+ }
+ }
+
+ cpu->dtb_compatible = arm_host_cpu_features.dtb_compatible;
+ cpu->isar = arm_host_cpu_features.isar;
+ cpu->env.features = arm_host_cpu_features.features;
+ cpu->midr = arm_host_cpu_features.midr;
+ cpu->reset_sctlr = arm_host_cpu_features.reset_sctlr;
+}
+
int whpx_init_vcpu(CPUState *cpu)
{
HRESULT hr;
diff --git a/target/arm/whpx_arm.h b/target/arm/whpx_arm.h
index de7406b66f..df65fd753c 100644
--- a/target/arm/whpx_arm.h
+++ b/target/arm/whpx_arm.h
@@ -12,5 +12,6 @@
#include "target/arm/cpu-qom.h"

uint32_t whpx_arm_get_ipa_bit_size(void);
+void whpx_arm_set_cpu_features_from_host(ARMCPU *cpu);

#endif
--
2.50.1 (Apple Git-155)