Merge tag 'hyperv-fixes-signed-20211117' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux

Pull hyperv fixes from Wei Liu:

 - Fix ring size calculation for balloon driver (Boqun Feng)

 - Fix issues in Hyper-V setup code (Sean Christopherson)

* tag 'hyperv-fixes-signed-20211117' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux:
  x86/hyperv: Move required MSRs check to initial platform probing
  x86/hyperv: Fix NULL deref in set_hv_tscchange_cb() if Hyper-V setup fails
  Drivers: hv: balloon: Use VMBUS_RING_SIZE() wrapper for dm_ring_size

Author: torvalds

arch/x86/hyperv/hv_init.c

@@ -177,6 +177,9 @@ void set_hv_tscchange_cb(void (*cb)(void))
 		return;
 	}
 
+	if (!hv_vp_index)
+		return;
+
 	hv_reenlightenment_cb = cb;
 
 	/* Make sure callback is registered before we write to MSRs */
@@ -383,20 +386,13 @@ static void __init hv_get_partition_id(void)
  */
 void __init hyperv_init(void)
 {
-	u64 guest_id, required_msrs;
+	u64 guest_id;
 	union hv_x64_msr_hypercall_contents hypercall_msr;
 	int cpuhp;
 
 	if (x86_hyper_type != X86_HYPER_MS_HYPERV)
 		return;
 
-	/* Absolutely required MSRs */
-	required_msrs = HV_MSR_HYPERCALL_AVAILABLE |
-		HV_MSR_VP_INDEX_AVAILABLE;
-
-	if ((ms_hyperv.features & required_msrs) != required_msrs)
-		return;
-
 	if (hv_common_init())
 		return;
 

arch/x86/kernel/cpu/mshyperv.c

@@ -163,12 +163,22 @@ static uint32_t  __init ms_hyperv_platform(void)
 	cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS,
 	      &eax, &hyp_signature[0], &hyp_signature[1], &hyp_signature[2]);
 
-	if (eax >= HYPERV_CPUID_MIN &&
-	    eax <= HYPERV_CPUID_MAX &&
-	    !memcmp("Microsoft Hv", hyp_signature, 12))
-		return HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
+	if (eax < HYPERV_CPUID_MIN || eax > HYPERV_CPUID_MAX ||
+	    memcmp("Microsoft Hv", hyp_signature, 12))
+		return 0;
 
-	return 0;
+	/* HYPERCALL and VP_INDEX MSRs are mandatory for all features. */
+	eax = cpuid_eax(HYPERV_CPUID_FEATURES);
+	if (!(eax & HV_MSR_HYPERCALL_AVAILABLE)) {
+		pr_warn("x86/hyperv: HYPERCALL MSR not available.\n");
+		return 0;
+	}
+	if (!(eax & HV_MSR_VP_INDEX_AVAILABLE)) {
+		pr_warn("x86/hyperv: VP_INDEX MSR not available.\n");
+		return 0;
+	}
+
+	return HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS;
 }
 
 static unsigned char hv_get_nmi_reason(void)

drivers/hv/hv_balloon.c

@@ -480,7 +480,7 @@ module_param(pressure_report_delay, uint, (S_IRUGO | S_IWUSR));
 MODULE_PARM_DESC(pressure_report_delay, "Delay in secs in reporting pressure");
 static atomic_t trans_id = ATOMIC_INIT(0);
 
-static int dm_ring_size = 20 * 1024;
+static int dm_ring_size = VMBUS_RING_SIZE(16 * 1024);
 
 /*
  * Driver specific state.