Add a test case to savic_test.c to verify the correct handling of HLT
instructions in Secure AVIC (SAVIC) enabled guests.

This validation is crucial for the SAVIC feature. With SAVIC, the IRR
is managed in the guest's private memory (the APIC backing page), making
it invisible to the hypervisor. In the absence of idle HLT intercept,
the hypervisor would be unaware of pending interrupts in the IRR and
would incorrectly block the vCPU.

Additionally, verify the corresponding ISR and EOI behavior for the
delivered interrupt within the SAVIC model.

Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
---
 tools/testing/selftests/kvm/x86/savic_test.c | 57 +++++++++++++++++++-
 1 file changed, 55 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/x86/savic_test.c b/tools/testing/selftests/kvm/x86/savic_test.c
index bac56f85caea..9108ac0077a9 100644
--- a/tools/testing/selftests/kvm/x86/savic_test.c
+++ b/tools/testing/selftests/kvm/x86/savic_test.c
@@ -14,7 +14,10 @@
 #include "savic.h"
 
 #define NR_SAVIC_VCPUS	1
+#define IDLE_HLT_INTR_VECTOR     0x30
+#define NUM_ITERATIONS 2000
 
+static bool irq_received;
 static struct kvm_vcpu *vcpus[NR_SAVIC_VCPUS];
 static pthread_t threads[NR_SAVIC_VCPUS];
 
@@ -24,6 +27,7 @@ static pthread_t threads[NR_SAVIC_VCPUS];
 
 enum savic_test_state {
 	SAVIC_TEST_STATE(SAVIC_APIC_MSR_ACCESSES),
+	SAVIC_TEST_STATE(SAVIC_IDLE_HALT),
 };
 
 #define SAVIC_GUEST_SYNC(sync, func) ({\
@@ -89,7 +93,8 @@ static void guest_verify_host_guest_reg(struct guest_apic_page *apage, uint32_t
 	hval = savic_hv_read_reg(reg);
 	__GUEST_ASSERT(gval == val, "Unexpected Guest %s 0x%lx, expected val:0x%lx\n",
 			regname, gval, val);
-	__GUEST_ASSERT(gval == gval2, "Unexpected Guest %s backing page value : 0x%lx, msr read val:0x%lx\n",
+	__GUEST_ASSERT(gval == gval2,
+			"Unexpected %s Guest backing page value : 0x%lx, msr read val:0x%lx\n",
 			regname, gval, gval2);
 
 	switch (reg) {
@@ -161,6 +166,7 @@ static void guest_savic_apic_msr_accesses(int id)
 	val = savic_read_reg(apage, APIC_IRR + APIC_REG_OFF(vec));
 	GUEST_ASSERT((val & BIT_ULL(APIC_VEC_POS(vec))) == BIT_ULL(APIC_VEC_POS(vec)));
 	savic_wrmsr(APIC_TASKPRI, 0x0);
+	savic_write_reg(apage, APIC_IRR + APIC_REG_OFF(vec), 0);
 
 	/* Triggers GP fault */
 	savic_rdmsr(APIC_EOI);
@@ -219,6 +225,43 @@ static void guest_savic_apic_msr_accesses(int id)
 	}
 }
 
+static void guest_idle_hlt_intr_handler(struct ex_regs *regs)
+{
+	struct guest_apic_page *apage = get_guest_apic_page();
+	uint32_t isr, reg;
+
+	WRITE_ONCE(irq_received, true);
+	reg = APIC_ISR + APIC_REG_OFF(IDLE_HLT_INTR_VECTOR);
+	isr = savic_read_reg(apage, reg);
+	__GUEST_ASSERT(isr & BIT(APIC_VEC_POS(IDLE_HLT_INTR_VECTOR)),
+				"Idle halt vector not set in APIC_ISR");
+	x2apic_write_reg(APIC_EOI, 0);
+	isr = savic_read_reg(apage, reg);
+	__GUEST_ASSERT(!(isr & BIT(APIC_VEC_POS(IDLE_HLT_INTR_VECTOR))),
+				"Idle halt vector set in APIC_ISR after EOI");
+}
+
+static void guest_savic_idle_halt(int id)
+{
+	uint32_t icr_val;
+	uint32_t irr;
+	int i;
+
+	x2apic_write_reg(APIC_TASKPRI, 0);
+	icr_val = (APIC_DEST_SELF | APIC_INT_ASSERT | IDLE_HLT_INTR_VECTOR);
+
+	for (i = 0; i < NUM_ITERATIONS; i++) {
+		asm volatile("cli");
+		x2apic_write_reg(APIC_ICR, icr_val);
+		irr = x2apic_read_reg(APIC_IRR + APIC_REG_OFF(IDLE_HLT_INTR_VECTOR));
+		__GUEST_ASSERT(irr & BIT(APIC_VEC_POS(IDLE_HLT_INTR_VECTOR)),
+				"Idle halt vector not set in APIC_IRR");
+		asm volatile("sti; hlt;" : : : "memory");
+		GUEST_ASSERT(READ_ONCE(irq_received));
+		WRITE_ONCE(irq_received, false);
+	}
+}
+
 static void guest_code(int id)
 {
 	GUEST_ASSERT(rdmsr(MSR_AMD64_SEV) & MSR_AMD64_SNP_SECURE_AVIC);
@@ -229,6 +272,8 @@ static void guest_code(int id)
 
 	SAVIC_GUEST_SYNC(SAVIC_APIC_MSR_ACCESSES, guest_savic_apic_msr_accesses);
 
+	SAVIC_GUEST_SYNC(SAVIC_IDLE_HALT, guest_savic_idle_halt);
+
 	GUEST_DONE();
 }
 
@@ -260,6 +305,12 @@ static void *vcpu_thread(void *arg)
 	return NULL;
 }
 
+static void install_exception_handlers(struct kvm_vm *vm)
+{
+	vm_install_exception_handler(vm, IDLE_HLT_INTR_VECTOR, guest_idle_hlt_intr_handler);
+	vm_install_exception_handler(vm, 29, savic_vc_handler);
+}
+
 int main(int argc, char *argv[])
 {
 	struct kvm_sev_init args = {
@@ -270,14 +321,16 @@ int main(int argc, char *argv[])
 
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_SEV_SNP));
 	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_SECURE_AVIC));
+	TEST_REQUIRE(this_cpu_has(X86_FEATURE_IDLE_HLT));
 
 	vm = _vm_sev_create_with_one_vcpu(KVM_X86_SNP_VM, guest_code, &vcpus[0], &args);
 
 	virt_pg_map(vm, APIC_DEFAULT_GPA, APIC_DEFAULT_GPA);
 
+	install_exception_handlers(vm);
+
 	vcpu_args_set(vcpus[0], 1, vcpus[0]->id);
 
-	vm_install_exception_handler(vm, 29, savic_vc_handler);
 	vm_sev_launch(vm, snp_default_policy(), NULL);
 
 	r = pthread_create(&threads[0], NULL, vcpu_thread, vcpus[0]);
-- 
2.34.1