The flag xen_have_vcpu_info_placement was needed to support Xen
hypervisors older than version 3.4. Today the Linux kernel requires
at least Xen 4.0 to be able to run, so xen_have_vcpu_info_placement
can be dropped.

This allows to let some functions return void now, as they can never
fail.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/xen/enlighten.c     | 97 +++++++++---------------------------
 arch/x86/xen/enlighten_hvm.c |  6 +--
 arch/x86/xen/enlighten_pv.c  | 28 ++---------
 arch/x86/xen/smp.c           | 24 ---------
 arch/x86/xen/xen-ops.h       |  4 +-
 5 files changed, 33 insertions(+), 126 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index c79bd0af2e8c..8a7bd3f4591e 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -81,21 +81,6 @@ EXPORT_SYMBOL(xen_start_flags);
  */
 struct shared_info *HYPERVISOR_shared_info = &xen_dummy_shared_info;
 
-/*
- * Flag to determine whether vcpu info placement is available on all
- * VCPUs.  We assume it is to start with, and then set it to zero on
- * the first failure.  This is because it can succeed on some VCPUs
- * and not others, since it can involve hypervisor memory allocation,
- * or because the guest failed to guarantee all the appropriate
- * constraints on all VCPUs (ie buffer can't cross a page boundary).
- *
- * Note that any particular CPU may be using a placed vcpu structure,
- * but we can only optimise if the all are.
- *
- * 0: not available, 1: available
- */
-int xen_have_vcpu_info_placement = 1;
-
 static int xen_cpu_up_online(unsigned int cpu)
 {
 	xen_init_lock_cpu(cpu);
@@ -121,10 +106,8 @@ int xen_cpuhp_setup(int (*cpu_up_prepare_cb)(unsigned int),
 	return rc >= 0 ? 0 : rc;
 }
 
-static int xen_vcpu_setup_restore(int cpu)
+static void xen_vcpu_setup_restore(int cpu)
 {
-	int rc = 0;
-
 	/* Any per_cpu(xen_vcpu) is stale, so reset it */
 	xen_vcpu_info_reset(cpu);
 
@@ -133,11 +116,8 @@ static int xen_vcpu_setup_restore(int cpu)
 	 * be handled by hotplug.
 	 */
 	if (xen_pv_domain() ||
-	    (xen_hvm_domain() && cpu_online(cpu))) {
-		rc = xen_vcpu_setup(cpu);
-	}
-
-	return rc;
+	    (xen_hvm_domain() && cpu_online(cpu)))
+		xen_vcpu_setup(cpu);
 }
 
 /*
@@ -147,7 +127,7 @@ static int xen_vcpu_setup_restore(int cpu)
  */
 void xen_vcpu_restore(void)
 {
-	int cpu, rc;
+	int cpu;
 
 	for_each_possible_cpu(cpu) {
 		bool other_cpu = (cpu != smp_processor_id());
@@ -167,20 +147,9 @@ void xen_vcpu_restore(void)
 		if (xen_pv_domain() || xen_feature(XENFEAT_hvm_safe_pvclock))
 			xen_setup_runstate_info(cpu);
 
-		rc = xen_vcpu_setup_restore(cpu);
-		if (rc)
-			pr_emerg_once("vcpu restore failed for cpu=%d err=%d. "
-					"System will hang.\n", cpu, rc);
-		/*
-		 * In case xen_vcpu_setup_restore() fails, do not bring up the
-		 * VCPU. This helps us avoid the resulting OOPS when the VCPU
-		 * accesses pvclock_vcpu_time via xen_vcpu (which is NULL.)
-		 * Note that this does not improve the situation much -- now the
-		 * VM hangs instead of OOPSing -- with the VCPUs that did not
-		 * fail, spinning in stop_machine(), waiting for the failed
-		 * VCPUs to come up.
-		 */
-		if (other_cpu && is_up && (rc == 0) &&
+		xen_vcpu_setup_restore(cpu);
+
+		if (other_cpu && is_up &&
 		    HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL))
 			BUG();
 	}
@@ -197,7 +166,7 @@ void xen_vcpu_info_reset(int cpu)
 	}
 }
 
-int xen_vcpu_setup(int cpu)
+void xen_vcpu_setup(int cpu)
 {
 	struct vcpu_register_vcpu_info info;
 	int err;
@@ -218,44 +187,26 @@ int xen_vcpu_setup(int cpu)
 	 */
 	if (xen_hvm_domain()) {
 		if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))
-			return 0;
+			return;
 	}
 
-	if (xen_have_vcpu_info_placement) {
-		vcpup = &per_cpu(xen_vcpu_info, cpu);
-		info.mfn = arbitrary_virt_to_mfn(vcpup);
-		info.offset = offset_in_page(vcpup);
+	vcpup = &per_cpu(xen_vcpu_info, cpu);
+	info.mfn = arbitrary_virt_to_mfn(vcpup);
+	info.offset = offset_in_page(vcpup);
 
-		/*
-		 * Check to see if the hypervisor will put the vcpu_info
-		 * structure where we want it, which allows direct access via
-		 * a percpu-variable.
-		 * N.B. This hypercall can _only_ be called once per CPU.
-		 * Subsequent calls will error out with -EINVAL. This is due to
-		 * the fact that hypervisor has no unregister variant and this
-		 * hypercall does not allow to over-write info.mfn and
-		 * info.offset.
-		 */
-		err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info,
-					 xen_vcpu_nr(cpu), &info);
-
-		if (err) {
-			pr_warn_once("register_vcpu_info failed: cpu=%d err=%d\n",
-				     cpu, err);
-			xen_have_vcpu_info_placement = 0;
-		} else {
-			/*
-			 * This cpu is using the registered vcpu info, even if
-			 * later ones fail to.
-			 */
-			per_cpu(xen_vcpu, cpu) = vcpup;
-		}
-	}
-
-	if (!xen_have_vcpu_info_placement)
-		xen_vcpu_info_reset(cpu);
+	/*
+	 * N.B. This hypercall can _only_ be called once per CPU.
+	 * Subsequent calls will error out with -EINVAL. This is due to
+	 * the fact that hypervisor has no unregister variant and this
+	 * hypercall does not allow to over-write info.mfn and
+	 * info.offset.
+	 */
+	err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, xen_vcpu_nr(cpu),
+				 &info);
+	if (err)
+		panic("register_vcpu_info failed: cpu=%d err=%d\n", cpu, err);
 
-	return ((per_cpu(xen_vcpu, cpu) == NULL) ? -ENODEV : 0);
+	per_cpu(xen_vcpu, cpu) = vcpup;
 }
 
 void xen_reboot(int reason)
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index e68ea5f4ad1c..42300941ec29 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -163,9 +163,9 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
 		per_cpu(xen_vcpu_id, cpu) = cpu_acpi_id(cpu);
 	else
 		per_cpu(xen_vcpu_id, cpu) = cpu;
-	rc = xen_vcpu_setup(cpu);
-	if (rc || !xen_have_vector_callback)
-		return rc;
+	xen_vcpu_setup(cpu);
+	if (!xen_have_vector_callback)
+		return 0;
 
 	if (xen_feature(XENFEAT_hvm_safe_pvclock))
 		xen_setup_timer(cpu);
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 349f780a1567..6719963901e5 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1018,31 +1018,13 @@ void __init xen_setup_vcpu_info_placement(void)
 	for_each_possible_cpu(cpu) {
 		/* Set up direct vCPU id mapping for PV guests. */
 		per_cpu(xen_vcpu_id, cpu) = cpu;
-
-		/*
-		 * xen_vcpu_setup(cpu) can fail  -- in which case it
-		 * falls back to the shared_info version for cpus
-		 * where xen_vcpu_nr(cpu) < MAX_VIRT_CPUS.
-		 *
-		 * xen_cpu_up_prepare_pv() handles the rest by failing
-		 * them in hotplug.
-		 */
-		(void) xen_vcpu_setup(cpu);
+		xen_vcpu_setup(cpu);
 	}
 
-	/*
-	 * xen_vcpu_setup managed to place the vcpu_info within the
-	 * percpu area for all cpus, so make use of it.
-	 */
-	if (xen_have_vcpu_info_placement) {
-		pv_ops.irq.save_fl = __PV_IS_CALLEE_SAVE(xen_save_fl_direct);
-		pv_ops.irq.irq_disable =
-			__PV_IS_CALLEE_SAVE(xen_irq_disable_direct);
-		pv_ops.irq.irq_enable =
-			__PV_IS_CALLEE_SAVE(xen_irq_enable_direct);
-		pv_ops.mmu.read_cr2 =
-			__PV_IS_CALLEE_SAVE(xen_read_cr2_direct);
-	}
+	pv_ops.irq.save_fl = __PV_IS_CALLEE_SAVE(xen_save_fl_direct);
+	pv_ops.irq.irq_disable = __PV_IS_CALLEE_SAVE(xen_irq_disable_direct);
+	pv_ops.irq.irq_enable = __PV_IS_CALLEE_SAVE(xen_irq_enable_direct);
+	pv_ops.mmu.read_cr2 = __PV_IS_CALLEE_SAVE(xen_read_cr2_direct);
 }
 
 static const struct pv_info xen_info __initconst = {
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index c1b2f764b29a..bafa61b1482f 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -121,34 +121,10 @@ int xen_smp_intr_init(unsigned int cpu)
 
 void __init xen_smp_cpus_done(unsigned int max_cpus)
 {
-	int cpu, rc, count = 0;
-
 	if (xen_hvm_domain())
 		native_smp_cpus_done(max_cpus);
 	else
 		calculate_max_logical_packages();
-
-	if (xen_have_vcpu_info_placement)
-		return;
-
-	for_each_online_cpu(cpu) {
-		if (xen_vcpu_nr(cpu) < MAX_VIRT_CPUS)
-			continue;
-
-		rc = remove_cpu(cpu);
-
-		if (rc == 0) {
-			/*
-			 * Reset vcpu_info so this cpu cannot be onlined again.
-			 */
-			xen_vcpu_info_reset(cpu);
-			count++;
-		} else {
-			pr_warn("%s: failed to bring CPU %d down, error %d\n",
-				__func__, cpu, rc);
-		}
-	}
-	WARN(count, "%s: brought %d CPUs offline\n", __func__, count);
 }
 
 void xen_smp_send_reschedule(int cpu)
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 8d7ec49a35fb..c2da84484b8d 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -75,9 +75,7 @@ irqreturn_t xen_debug_interrupt(int irq, void *dev_id);
 
 bool xen_vcpu_stolen(int vcpu);
 
-extern int xen_have_vcpu_info_placement;
-
-int xen_vcpu_setup(int cpu);
+void xen_vcpu_setup(int cpu);
 void xen_vcpu_info_reset(int cpu);
 void xen_setup_vcpu_info_placement(void);
 
-- 
2.26.2

On 9/22/21 6:31 AM, Juergen Gross wrote:
>  
> -	if (xen_have_vcpu_info_placement) {
> -		vcpup = &per_cpu(xen_vcpu_info, cpu);
> -		info.mfn = arbitrary_virt_to_mfn(vcpup);
> -		info.offset = offset_in_page(vcpup);
> +	vcpup = &per_cpu(xen_vcpu_info, cpu);
> +	info.mfn = arbitrary_virt_to_mfn(vcpup);
> +	info.offset = offset_in_page(vcpup);
>  
> -		/*
> -		 * Check to see if the hypervisor will put the vcpu_info
> -		 * structure where we want it, which allows direct access via
> -		 * a percpu-variable.
> -		 * N.B. This hypercall can _only_ be called once per CPU.
> -		 * Subsequent calls will error out with -EINVAL. This is due to
> -		 * the fact that hypervisor has no unregister variant and this
> -		 * hypercall does not allow to over-write info.mfn and
> -		 * info.offset.
> -		 */
> -		err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info,
> -					 xen_vcpu_nr(cpu), &info);
> -
> -		if (err) {
> -			pr_warn_once("register_vcpu_info failed: cpu=%d err=%d\n",
> -				     cpu, err);
> -			xen_have_vcpu_info_placement = 0;
> -		} else {
> -			/*
> -			 * This cpu is using the registered vcpu info, even if
> -			 * later ones fail to.
> -			 */
> -			per_cpu(xen_vcpu, cpu) = vcpup;
> -		}
> -	}
> -
> -	if (!xen_have_vcpu_info_placement)
> -		xen_vcpu_info_reset(cpu);
> +	/*
> +	 * N.B. This hypercall can _only_ be called once per CPU.
> +	 * Subsequent calls will error out with -EINVAL. This is due to
> +	 * the fact that hypervisor has no unregister variant and this
> +	 * hypercall does not allow to over-write info.mfn and
> +	 * info.offset.
> +	 */
> +	err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, xen_vcpu_nr(cpu),
> +				 &info);
> +	if (err)
> +		panic("register_vcpu_info failed: cpu=%d err=%d\n", cpu, err);
>  


This is change in behavior. Before if the hypercall failed we still try to boot. I am not sure we need to worry about this (since it's not clear it actually works)  but I'd at least mention this in the commit message.


-boris

On 22.09.21 23:43, Boris Ostrovsky wrote:
> 
> On 9/22/21 6:31 AM, Juergen Gross wrote:
>>   
>> -	if (xen_have_vcpu_info_placement) {
>> -		vcpup = &per_cpu(xen_vcpu_info, cpu);
>> -		info.mfn = arbitrary_virt_to_mfn(vcpup);
>> -		info.offset = offset_in_page(vcpup);
>> +	vcpup = &per_cpu(xen_vcpu_info, cpu);
>> +	info.mfn = arbitrary_virt_to_mfn(vcpup);
>> +	info.offset = offset_in_page(vcpup);
>>   
>> -		/*
>> -		 * Check to see if the hypervisor will put the vcpu_info
>> -		 * structure where we want it, which allows direct access via
>> -		 * a percpu-variable.
>> -		 * N.B. This hypercall can _only_ be called once per CPU.
>> -		 * Subsequent calls will error out with -EINVAL. This is due to
>> -		 * the fact that hypervisor has no unregister variant and this
>> -		 * hypercall does not allow to over-write info.mfn and
>> -		 * info.offset.
>> -		 */
>> -		err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info,
>> -					 xen_vcpu_nr(cpu), &info);
>> -
>> -		if (err) {
>> -			pr_warn_once("register_vcpu_info failed: cpu=%d err=%d\n",
>> -				     cpu, err);
>> -			xen_have_vcpu_info_placement = 0;
>> -		} else {
>> -			/*
>> -			 * This cpu is using the registered vcpu info, even if
>> -			 * later ones fail to.
>> -			 */
>> -			per_cpu(xen_vcpu, cpu) = vcpup;
>> -		}
>> -	}
>> -
>> -	if (!xen_have_vcpu_info_placement)
>> -		xen_vcpu_info_reset(cpu);
>> +	/*
>> +	 * N.B. This hypercall can _only_ be called once per CPU.
>> +	 * Subsequent calls will error out with -EINVAL. This is due to
>> +	 * the fact that hypervisor has no unregister variant and this
>> +	 * hypercall does not allow to over-write info.mfn and
>> +	 * info.offset.
>> +	 */
>> +	err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, xen_vcpu_nr(cpu),
>> +				 &info);
>> +	if (err)
>> +		panic("register_vcpu_info failed: cpu=%d err=%d\n", cpu, err);
>>   
> 
> 
> This is change in behavior. Before if the hypercall failed we still try to boot. I am not sure we need to worry about this (since it's not clear it actually works)  but I'd at least mention this in the commit message.

Hmm, maybe I should have been more explicit saying that the hypercall
was introduced in Xen 3.4, and only reason of failure is either an
illegal vcpu, an invalid mapping specification, or a try to reissue the
hypercall for a vcpu. None of those should ever happen.


Juergen

On 9/23/21 12:44 AM, Juergen Gross wrote:
>
> Hmm, maybe I should have been more explicit saying that the hypercall
> was introduced in Xen 3.4, and only reason of failure is either an
> illegal vcpu, an invalid mapping specification, or a try to reissue the
> hypercall for a vcpu. None of those should ever happen.
>

That last sentence -- famous last words ;-) But yes, sure.


Assuming both patches adjust their commit messages and the typo


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>