From: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>

On x86, the HYPERVISOR_CALLBACK_VECTOR is used to receive synthetic
interrupts (SINTs) from the hypervisor for doorbells and intercepts.
There is no such vector reserved for arm64.

On arm64, the INTID for SINTs should be in the SGI or PPI range. The
hypervisor exposes a virtual device in the ACPI that reserves a
PPI for this use. Introduce a platform_driver that binds to this ACPI
device and obtains the interrupt vector that can be used for SINTs.

To better unify x86 and arm64 paths, introduce mshv_sint_vector_init() that
either registers the platform_driver and obtains the INTID (arm64) or
just uses HYPERVISOR_CALLBACK_VECTOR as the interrupt vector (x86).

Signed-off-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
---
 drivers/hv/mshv_synic.c | 163 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 156 insertions(+), 7 deletions(-)

diff --git a/drivers/hv/mshv_synic.c b/drivers/hv/mshv_synic.c
index 98c58755846d..de5fee6e9f29 100644
--- a/drivers/hv/mshv_synic.c
+++ b/drivers/hv/mshv_synic.c
@@ -10,17 +10,24 @@
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
+#include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/random.h>
 #include <linux/cpuhotplug.h>
 #include <linux/reboot.h>
 #include <asm/mshyperv.h>
+#include <linux/platform_device.h>
+#include <linux/acpi.h>
 
 #include "mshv_eventfd.h"
 #include "mshv.h"
 
 static int synic_cpuhp_online;
 static struct hv_synic_pages __percpu *synic_pages;
+static int mshv_sint_vector = -1; /* hwirq for the SynIC SINTs */
+#ifndef HYPERVISOR_CALLBACK_VECTOR
+static int mshv_sint_irq = -1; /* Linux IRQ for mshv_sint_vector */
+#endif
 
 static u32 synic_event_ring_get_queued_port(u32 sint_index)
 {
@@ -456,9 +463,7 @@ static int mshv_synic_cpu_init(unsigned int cpu)
 	union hv_synic_simp simp;
 	union hv_synic_siefp siefp;
 	union hv_synic_sirbp sirbp;
-#ifdef HYPERVISOR_CALLBACK_VECTOR
 	union hv_synic_sint sint;
-#endif
 	union hv_synic_scontrol sctrl;
 	struct hv_synic_pages *spages = this_cpu_ptr(synic_pages);
 	struct hv_message_page **msg_page = &spages->hyp_synic_message_page;
@@ -501,10 +506,13 @@ static int mshv_synic_cpu_init(unsigned int cpu)
 
 	hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
 
-#ifdef HYPERVISOR_CALLBACK_VECTOR
+#ifndef HYPERVISOR_CALLBACK_VECTOR
+	enable_percpu_irq(mshv_sint_irq, 0);
+#endif
+
 	/* Enable intercepts */
 	sint.as_uint64 = 0;
-	sint.vector = HYPERVISOR_CALLBACK_VECTOR;
+	sint.vector = mshv_sint_vector;
 	sint.masked = false;
 	sint.auto_eoi = hv_recommend_using_aeoi();
 	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_INTERCEPTION_SINT_INDEX,
@@ -512,13 +520,12 @@ static int mshv_synic_cpu_init(unsigned int cpu)
 
 	/* Doorbell SINT */
 	sint.as_uint64 = 0;
-	sint.vector = HYPERVISOR_CALLBACK_VECTOR;
+	sint.vector = mshv_sint_vector;
 	sint.masked = false;
 	sint.as_intercept = 1;
 	sint.auto_eoi = hv_recommend_using_aeoi();
 	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_DOORBELL_SINT_INDEX,
 			      sint.as_uint64);
-#endif
 
 	/* Enable global synic bit */
 	sctrl.as_uint64 = hv_get_non_nested_msr(HV_MSR_SCONTROL);
@@ -573,6 +580,10 @@ static int mshv_synic_cpu_exit(unsigned int cpu)
 	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_DOORBELL_SINT_INDEX,
 			      sint.as_uint64);
 
+#ifndef HYPERVISOR_CALLBACK_VECTOR
+	disable_percpu_irq(mshv_sint_irq);
+#endif
+
 	/* Disable Synic's event ring page */
 	sirbp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIRBP);
 	sirbp.sirbp_enabled = false;
@@ -680,14 +691,149 @@ static struct notifier_block mshv_synic_reboot_nb = {
 	.notifier_call = mshv_synic_reboot_notify,
 };
 
+#ifndef HYPERVISOR_CALLBACK_VECTOR
+#ifdef CONFIG_ACPI
+static long __percpu *mshv_evt;
+
+static acpi_status mshv_walk_resources(struct acpi_resource *res, void *ctx)
+{
+	struct resource r;
+
+	if (res->type == ACPI_RESOURCE_TYPE_EXTENDED_IRQ) {
+		if (!acpi_dev_resource_interrupt(res, 0, &r)) {
+			pr_err("Unable to parse MSHV ACPI interrupt\n");
+			return AE_ERROR;
+		}
+		/* ARM64 INTID */
+		mshv_sint_vector = res->data.extended_irq.interrupts[0];
+		/* Linux IRQ number */
+		mshv_sint_irq = r.start;
+	}
+
+	return AE_OK;
+}
+
+static irqreturn_t mshv_percpu_isr(int irq, void *dev_id)
+{
+	mshv_isr();
+	return IRQ_HANDLED;
+}
+
+static int mshv_sint_probe(struct platform_device *pdev)
+{
+	acpi_status result;
+	int ret;
+	struct acpi_device *device = ACPI_COMPANION(&pdev->dev);
+
+	result = acpi_walk_resources(device->handle, METHOD_NAME__CRS,
+					mshv_walk_resources, NULL);
+	if (ACPI_FAILURE(result)) {
+		ret = -ENODEV;
+		goto out_fail;
+	}
+
+	mshv_evt = alloc_percpu(long);
+	if (!mshv_evt) {
+		ret = -ENOMEM;
+		goto out_fail;
+	}
+
+	ret = request_percpu_irq(mshv_sint_irq, mshv_percpu_isr, "MSHV",
+		mshv_evt);
+	if (ret)
+		goto free_evt;
+
+	return 0;
+
+free_evt:
+	free_percpu(mshv_evt);
+out_fail:
+	mshv_sint_vector = -1;
+	mshv_sint_irq = -1;
+	return ret;
+}
+
+static void mshv_sint_remove(struct platform_device *pdev)
+{
+	free_percpu_irq(mshv_sint_irq, mshv_evt);
+	free_percpu(mshv_evt);
+}
+#else
+static int mshv_sint_probe(struct platform_device *pdev)
+{
+	return -ENODEV;
+}
+
+static void mshv_sint_remove(struct platform_device *pdev)
+{
+}
+#endif
+
+static const __maybe_unused struct acpi_device_id mshv_sint_device_ids[] = {
+	{"MSFT1003", 0},
+	{"", 0},
+};
+
+static struct platform_driver mshv_sint_drv = {
+	.probe = mshv_sint_probe,
+	.remove = mshv_sint_remove,
+	.driver = {
+		.name = "mshv_sint",
+		.acpi_match_table = ACPI_PTR(mshv_sint_device_ids),
+		.probe_type = PROBE_FORCE_SYNCHRONOUS,
+	},
+};
+
+static int __init mshv_sint_vector_init(void)
+{
+	int ret;
+
+	if (acpi_disabled)
+		return -ENODEV;
+
+	ret = platform_driver_register(&mshv_sint_drv);
+	if (ret)
+		return ret;
+
+	if (mshv_sint_vector == -1 || mshv_sint_irq == -1) {
+		platform_driver_unregister(&mshv_sint_drv);
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static void mshv_sint_vector_cleanup(void)
+{
+	platform_driver_unregister(&mshv_sint_drv);
+}
+#else /* HYPERVISOR_CALLBACK_VECTOR */
+static int __init mshv_sint_vector_init(void)
+{
+	mshv_sint_vector = HYPERVISOR_CALLBACK_VECTOR;
+	return 0;
+}
+
+static void mshv_sint_vector_cleanup(void)
+{
+}
+#endif /* HYPERVISOR_CALLBACK_VECTOR */
+
 int __init mshv_synic_init(struct device *dev)
 {
 	int ret = 0;
 
+	ret = mshv_sint_vector_init();
+	if (ret) {
+		dev_err(dev, "Failed to get MSHV SINT vector: %i\n", ret);
+		return ret;
+	}
+
 	synic_pages = alloc_percpu(struct hv_synic_pages);
 	if (!synic_pages) {
 		dev_err(dev, "Failed to allocate percpu synic page\n");
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto sint_vector_cleanup;
 	}
 
 	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mshv_synic",
@@ -712,6 +858,8 @@ int __init mshv_synic_init(struct device *dev)
 	cpuhp_remove_state(synic_cpuhp_online);
 free_synic_pages:
 	free_percpu(synic_pages);
+sint_vector_cleanup:
+	mshv_sint_vector_cleanup();
 	return ret;
 }
 
@@ -721,4 +869,5 @@ void mshv_synic_cleanup(void)
 		unregister_reboot_notifier(&mshv_synic_reboot_nb);
 	cpuhp_remove_state(synic_cpuhp_online);
 	free_percpu(synic_pages);
+	mshv_sint_vector_cleanup();
 }
-- 
2.34.1

On Mon, Feb 02, 2026 at 06:27:06PM +0000, Anirudh Rayabharam wrote:
> From: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
> 
> On x86, the HYPERVISOR_CALLBACK_VECTOR is used to receive synthetic
> interrupts (SINTs) from the hypervisor for doorbells and intercepts.
> There is no such vector reserved for arm64.
> 
> On arm64, the INTID for SINTs should be in the SGI or PPI range. The
> hypervisor exposes a virtual device in the ACPI that reserves a
> PPI for this use. Introduce a platform_driver that binds to this ACPI
> device and obtains the interrupt vector that can be used for SINTs.
> 
> To better unify x86 and arm64 paths, introduce mshv_sint_vector_init() that
> either registers the platform_driver and obtains the INTID (arm64) or
> just uses HYPERVISOR_CALLBACK_VECTOR as the interrupt vector (x86).
> 
> Signed-off-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
> ---
>  drivers/hv/mshv_synic.c | 163 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 156 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/hv/mshv_synic.c b/drivers/hv/mshv_synic.c
> index 98c58755846d..de5fee6e9f29 100644
> --- a/drivers/hv/mshv_synic.c
> +++ b/drivers/hv/mshv_synic.c
> @@ -10,17 +10,24 @@
>  #include <linux/kernel.h>
>  #include <linux/slab.h>
>  #include <linux/mm.h>
> +#include <linux/interrupt.h>
>  #include <linux/io.h>
>  #include <linux/random.h>
>  #include <linux/cpuhotplug.h>
>  #include <linux/reboot.h>
>  #include <asm/mshyperv.h>
> +#include <linux/platform_device.h>
> +#include <linux/acpi.h>
>  
>  #include "mshv_eventfd.h"
>  #include "mshv.h"
>  
>  static int synic_cpuhp_online;
>  static struct hv_synic_pages __percpu *synic_pages;
> +static int mshv_sint_vector = -1; /* hwirq for the SynIC SINTs */
> +#ifndef HYPERVISOR_CALLBACK_VECTOR
> +static int mshv_sint_irq = -1; /* Linux IRQ for mshv_sint_vector */
> +#endif
>  
>  static u32 synic_event_ring_get_queued_port(u32 sint_index)
>  {
> @@ -456,9 +463,7 @@ static int mshv_synic_cpu_init(unsigned int cpu)
>  	union hv_synic_simp simp;
>  	union hv_synic_siefp siefp;
>  	union hv_synic_sirbp sirbp;
> -#ifdef HYPERVISOR_CALLBACK_VECTOR
>  	union hv_synic_sint sint;
> -#endif
>  	union hv_synic_scontrol sctrl;
>  	struct hv_synic_pages *spages = this_cpu_ptr(synic_pages);
>  	struct hv_message_page **msg_page = &spages->hyp_synic_message_page;
> @@ -501,10 +506,13 @@ static int mshv_synic_cpu_init(unsigned int cpu)
>  
>  	hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
>  
> -#ifdef HYPERVISOR_CALLBACK_VECTOR
> +#ifndef HYPERVISOR_CALLBACK_VECTOR
> +	enable_percpu_irq(mshv_sint_irq, 0);
> +#endif
> +
>  	/* Enable intercepts */
>  	sint.as_uint64 = 0;
> -	sint.vector = HYPERVISOR_CALLBACK_VECTOR;
> +	sint.vector = mshv_sint_vector;
>  	sint.masked = false;
>  	sint.auto_eoi = hv_recommend_using_aeoi();
>  	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_INTERCEPTION_SINT_INDEX,
> @@ -512,13 +520,12 @@ static int mshv_synic_cpu_init(unsigned int cpu)
>  
>  	/* Doorbell SINT */
>  	sint.as_uint64 = 0;
> -	sint.vector = HYPERVISOR_CALLBACK_VECTOR;
> +	sint.vector = mshv_sint_vector;
>  	sint.masked = false;
>  	sint.as_intercept = 1;
>  	sint.auto_eoi = hv_recommend_using_aeoi();
>  	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_DOORBELL_SINT_INDEX,
>  			      sint.as_uint64);
> -#endif
>  
>  	/* Enable global synic bit */
>  	sctrl.as_uint64 = hv_get_non_nested_msr(HV_MSR_SCONTROL);
> @@ -573,6 +580,10 @@ static int mshv_synic_cpu_exit(unsigned int cpu)
>  	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_DOORBELL_SINT_INDEX,
>  			      sint.as_uint64);
>  
> +#ifndef HYPERVISOR_CALLBACK_VECTOR
> +	disable_percpu_irq(mshv_sint_irq);
> +#endif
> +
>  	/* Disable Synic's event ring page */
>  	sirbp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIRBP);
>  	sirbp.sirbp_enabled = false;
> @@ -680,14 +691,149 @@ static struct notifier_block mshv_synic_reboot_nb = {
>  	.notifier_call = mshv_synic_reboot_notify,
>  };
>  
> +#ifndef HYPERVISOR_CALLBACK_VECTOR

You have introduced 4 ifdef branches (one aroung the variable and three
in mshv_synic_cpu_init) and then you still have a big ifdef branch here.

Why is it better than simply introducing two different
mshv_synic_cpu_init functions and have a single big ifdef instead
(especially giving that this code is arch-specific anyway and thus won't
bloat the binary)?

This will also allows to get rid of redundant mshv_sint_vector variable
on x86.

Thanks,
Stanislav

> +#ifdef CONFIG_ACPI
> +static long __percpu *mshv_evt;
> +
> +static acpi_status mshv_walk_resources(struct acpi_resource *res, void *ctx)
> +{
> +	struct resource r;
> +
> +	if (res->type == ACPI_RESOURCE_TYPE_EXTENDED_IRQ) {
> +		if (!acpi_dev_resource_interrupt(res, 0, &r)) {
> +			pr_err("Unable to parse MSHV ACPI interrupt\n");
> +			return AE_ERROR;
> +		}
> +		/* ARM64 INTID */
> +		mshv_sint_vector = res->data.extended_irq.interrupts[0];
> +		/* Linux IRQ number */
> +		mshv_sint_irq = r.start;
> +	}
> +
> +	return AE_OK;
> +}
> +
> +static irqreturn_t mshv_percpu_isr(int irq, void *dev_id)
> +{
> +	mshv_isr();
> +	return IRQ_HANDLED;
> +}
> +
> +static int mshv_sint_probe(struct platform_device *pdev)
> +{
> +	acpi_status result;
> +	int ret;
> +	struct acpi_device *device = ACPI_COMPANION(&pdev->dev);
> +
> +	result = acpi_walk_resources(device->handle, METHOD_NAME__CRS,
> +					mshv_walk_resources, NULL);
> +	if (ACPI_FAILURE(result)) {
> +		ret = -ENODEV;
> +		goto out_fail;
> +	}
> +
> +	mshv_evt = alloc_percpu(long);
> +	if (!mshv_evt) {
> +		ret = -ENOMEM;
> +		goto out_fail;
> +	}
> +
> +	ret = request_percpu_irq(mshv_sint_irq, mshv_percpu_isr, "MSHV",
> +		mshv_evt);
> +	if (ret)
> +		goto free_evt;
> +
> +	return 0;
> +
> +free_evt:
> +	free_percpu(mshv_evt);
> +out_fail:
> +	mshv_sint_vector = -1;
> +	mshv_sint_irq = -1;
> +	return ret;
> +}
> +
> +static void mshv_sint_remove(struct platform_device *pdev)
> +{
> +	free_percpu_irq(mshv_sint_irq, mshv_evt);
> +	free_percpu(mshv_evt);
> +}
> +#else
> +static int mshv_sint_probe(struct platform_device *pdev)
> +{
> +	return -ENODEV;
> +}
> +
> +static void mshv_sint_remove(struct platform_device *pdev)
> +{
> +}
> +#endif
> +
> +static const __maybe_unused struct acpi_device_id mshv_sint_device_ids[] = {
> +	{"MSFT1003", 0},
> +	{"", 0},
> +};
> +
> +static struct platform_driver mshv_sint_drv = {
> +	.probe = mshv_sint_probe,
> +	.remove = mshv_sint_remove,
> +	.driver = {
> +		.name = "mshv_sint",
> +		.acpi_match_table = ACPI_PTR(mshv_sint_device_ids),
> +		.probe_type = PROBE_FORCE_SYNCHRONOUS,
> +	},
> +};
> +
> +static int __init mshv_sint_vector_init(void)
> +{
> +	int ret;
> +
> +	if (acpi_disabled)
> +		return -ENODEV;
> +
> +	ret = platform_driver_register(&mshv_sint_drv);
> +	if (ret)
> +		return ret;
> +
> +	if (mshv_sint_vector == -1 || mshv_sint_irq == -1) {
> +		platform_driver_unregister(&mshv_sint_drv);
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
> +static void mshv_sint_vector_cleanup(void)
> +{
> +	platform_driver_unregister(&mshv_sint_drv);
> +}
> +#else /* HYPERVISOR_CALLBACK_VECTOR */
> +static int __init mshv_sint_vector_init(void)
> +{
> +	mshv_sint_vector = HYPERVISOR_CALLBACK_VECTOR;
> +	return 0;
> +}
> +
> +static void mshv_sint_vector_cleanup(void)
> +{
> +}
> +#endif /* HYPERVISOR_CALLBACK_VECTOR */
> +
>  int __init mshv_synic_init(struct device *dev)
>  {
>  	int ret = 0;
>  
> +	ret = mshv_sint_vector_init();
> +	if (ret) {
> +		dev_err(dev, "Failed to get MSHV SINT vector: %i\n", ret);
> +		return ret;
> +	}
> +
>  	synic_pages = alloc_percpu(struct hv_synic_pages);
>  	if (!synic_pages) {
>  		dev_err(dev, "Failed to allocate percpu synic page\n");
> -		return -ENOMEM;
> +		ret = -ENOMEM;
> +		goto sint_vector_cleanup;
>  	}
>  
>  	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mshv_synic",
> @@ -712,6 +858,8 @@ int __init mshv_synic_init(struct device *dev)
>  	cpuhp_remove_state(synic_cpuhp_online);
>  free_synic_pages:
>  	free_percpu(synic_pages);
> +sint_vector_cleanup:
> +	mshv_sint_vector_cleanup();
>  	return ret;
>  }
>  
> @@ -721,4 +869,5 @@ void mshv_synic_cleanup(void)
>  		unregister_reboot_notifier(&mshv_synic_reboot_nb);
>  	cpuhp_remove_state(synic_cpuhp_online);
>  	free_percpu(synic_pages);
> +	mshv_sint_vector_cleanup();
>  }
> -- 
> 2.34.1
>

On Mon, Feb 02, 2026 at 11:13:34AM -0800, Stanislav Kinsburskii wrote:
> On Mon, Feb 02, 2026 at 06:27:06PM +0000, Anirudh Rayabharam wrote:
> > From: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
> > 
> > On x86, the HYPERVISOR_CALLBACK_VECTOR is used to receive synthetic
> > interrupts (SINTs) from the hypervisor for doorbells and intercepts.
> > There is no such vector reserved for arm64.
> > 
> > On arm64, the INTID for SINTs should be in the SGI or PPI range. The
> > hypervisor exposes a virtual device in the ACPI that reserves a
> > PPI for this use. Introduce a platform_driver that binds to this ACPI
> > device and obtains the interrupt vector that can be used for SINTs.
> > 
> > To better unify x86 and arm64 paths, introduce mshv_sint_vector_init() that
> > either registers the platform_driver and obtains the INTID (arm64) or
> > just uses HYPERVISOR_CALLBACK_VECTOR as the interrupt vector (x86).
> > 
> > Signed-off-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
> > ---
> >  drivers/hv/mshv_synic.c | 163 ++++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 156 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/hv/mshv_synic.c b/drivers/hv/mshv_synic.c
> > index 98c58755846d..de5fee6e9f29 100644
> > --- a/drivers/hv/mshv_synic.c
> > +++ b/drivers/hv/mshv_synic.c
> > @@ -10,17 +10,24 @@
> >  #include <linux/kernel.h>
> >  #include <linux/slab.h>
> >  #include <linux/mm.h>
> > +#include <linux/interrupt.h>
> >  #include <linux/io.h>
> >  #include <linux/random.h>
> >  #include <linux/cpuhotplug.h>
> >  #include <linux/reboot.h>
> >  #include <asm/mshyperv.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/acpi.h>
> >  
> >  #include "mshv_eventfd.h"
> >  #include "mshv.h"
> >  
> >  static int synic_cpuhp_online;
> >  static struct hv_synic_pages __percpu *synic_pages;
> > +static int mshv_sint_vector = -1; /* hwirq for the SynIC SINTs */
> > +#ifndef HYPERVISOR_CALLBACK_VECTOR
> > +static int mshv_sint_irq = -1; /* Linux IRQ for mshv_sint_vector */
> > +#endif
> >  
> >  static u32 synic_event_ring_get_queued_port(u32 sint_index)
> >  {
> > @@ -456,9 +463,7 @@ static int mshv_synic_cpu_init(unsigned int cpu)
> >  	union hv_synic_simp simp;
> >  	union hv_synic_siefp siefp;
> >  	union hv_synic_sirbp sirbp;
> > -#ifdef HYPERVISOR_CALLBACK_VECTOR
> >  	union hv_synic_sint sint;
> > -#endif
> >  	union hv_synic_scontrol sctrl;
> >  	struct hv_synic_pages *spages = this_cpu_ptr(synic_pages);
> >  	struct hv_message_page **msg_page = &spages->hyp_synic_message_page;
> > @@ -501,10 +506,13 @@ static int mshv_synic_cpu_init(unsigned int cpu)
> >  
> >  	hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
> >  
> > -#ifdef HYPERVISOR_CALLBACK_VECTOR
> > +#ifndef HYPERVISOR_CALLBACK_VECTOR
> > +	enable_percpu_irq(mshv_sint_irq, 0);
> > +#endif
> > +
> >  	/* Enable intercepts */
> >  	sint.as_uint64 = 0;
> > -	sint.vector = HYPERVISOR_CALLBACK_VECTOR;
> > +	sint.vector = mshv_sint_vector;
> >  	sint.masked = false;
> >  	sint.auto_eoi = hv_recommend_using_aeoi();
> >  	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_INTERCEPTION_SINT_INDEX,
> > @@ -512,13 +520,12 @@ static int mshv_synic_cpu_init(unsigned int cpu)
> >  
> >  	/* Doorbell SINT */
> >  	sint.as_uint64 = 0;
> > -	sint.vector = HYPERVISOR_CALLBACK_VECTOR;
> > +	sint.vector = mshv_sint_vector;
> >  	sint.masked = false;
> >  	sint.as_intercept = 1;
> >  	sint.auto_eoi = hv_recommend_using_aeoi();
> >  	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_DOORBELL_SINT_INDEX,
> >  			      sint.as_uint64);
> > -#endif
> >  
> >  	/* Enable global synic bit */
> >  	sctrl.as_uint64 = hv_get_non_nested_msr(HV_MSR_SCONTROL);
> > @@ -573,6 +580,10 @@ static int mshv_synic_cpu_exit(unsigned int cpu)
> >  	hv_set_non_nested_msr(HV_MSR_SINT0 + HV_SYNIC_DOORBELL_SINT_INDEX,
> >  			      sint.as_uint64);
> >  
> > +#ifndef HYPERVISOR_CALLBACK_VECTOR
> > +	disable_percpu_irq(mshv_sint_irq);
> > +#endif
> > +
> >  	/* Disable Synic's event ring page */
> >  	sirbp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIRBP);
> >  	sirbp.sirbp_enabled = false;
> > @@ -680,14 +691,149 @@ static struct notifier_block mshv_synic_reboot_nb = {
> >  	.notifier_call = mshv_synic_reboot_notify,
> >  };
> >  
> > +#ifndef HYPERVISOR_CALLBACK_VECTOR
> 
> You have introduced 4 ifdef branches (one aroung the variable and three
> in mshv_synic_cpu_init) and then you still have a big ifdef branch here.

If it is ifdefs you're counting I could remove the one's around
mshv_sint_irq and then wherever it is used I could do:

	if (mshv_sint_irq != -1)
		<do something...>

This will reduce #ifdefs but will mean one more variable in the
!HYPERVISOR_CALLBACK_VECTOR case (which I believe would be optimized
away anyway).

> 
> Why is it better than simply introducing two different
> mshv_synic_cpu_init functions and have a single big ifdef instead
> (especially giving that this code is arch-specific anyway and thus won't
> bloat the binary)?

There are only two lines of code in mshv_synic_cpu_init that are inside
ifdefs. It doesn't make sense to write the exact same function twice
with just two lines different. It's not a short function, so anybody
reading it would have a pretty hard time figuring out which lines are
different.

Big ifdef here is unavoidable because the whole platform_driver part has
to be implemented.

Other ifdefs are so small that they shouldn't be jarring when reading
the code.

> 
> This will also allows to get rid of redundant mshv_sint_vector variable
> on x86.

Yeah, but the trade off (two copies of the largely same
mshv_synic_cpu_init) is horrible. And the variable would be optimized
away anyway.

Thanks,
Anirudh.

> 
> Thanks,
> Stanislav
> 
> > +#ifdef CONFIG_ACPI
> > +static long __percpu *mshv_evt;
> > +
> > +static acpi_status mshv_walk_resources(struct acpi_resource *res, void *ctx)
> > +{
> > +	struct resource r;
> > +
> > +	if (res->type == ACPI_RESOURCE_TYPE_EXTENDED_IRQ) {
> > +		if (!acpi_dev_resource_interrupt(res, 0, &r)) {
> > +			pr_err("Unable to parse MSHV ACPI interrupt\n");
> > +			return AE_ERROR;
> > +		}
> > +		/* ARM64 INTID */
> > +		mshv_sint_vector = res->data.extended_irq.interrupts[0];
> > +		/* Linux IRQ number */
> > +		mshv_sint_irq = r.start;
> > +	}
> > +
> > +	return AE_OK;
> > +}
> > +
> > +static irqreturn_t mshv_percpu_isr(int irq, void *dev_id)
> > +{
> > +	mshv_isr();
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +static int mshv_sint_probe(struct platform_device *pdev)
> > +{
> > +	acpi_status result;
> > +	int ret;
> > +	struct acpi_device *device = ACPI_COMPANION(&pdev->dev);
> > +
> > +	result = acpi_walk_resources(device->handle, METHOD_NAME__CRS,
> > +					mshv_walk_resources, NULL);
> > +	if (ACPI_FAILURE(result)) {
> > +		ret = -ENODEV;
> > +		goto out_fail;
> > +	}
> > +
> > +	mshv_evt = alloc_percpu(long);
> > +	if (!mshv_evt) {
> > +		ret = -ENOMEM;
> > +		goto out_fail;
> > +	}
> > +
> > +	ret = request_percpu_irq(mshv_sint_irq, mshv_percpu_isr, "MSHV",
> > +		mshv_evt);
> > +	if (ret)
> > +		goto free_evt;
> > +
> > +	return 0;
> > +
> > +free_evt:
> > +	free_percpu(mshv_evt);
> > +out_fail:
> > +	mshv_sint_vector = -1;
> > +	mshv_sint_irq = -1;
> > +	return ret;
> > +}
> > +
> > +static void mshv_sint_remove(struct platform_device *pdev)
> > +{
> > +	free_percpu_irq(mshv_sint_irq, mshv_evt);
> > +	free_percpu(mshv_evt);
> > +}
> > +#else
> > +static int mshv_sint_probe(struct platform_device *pdev)
> > +{
> > +	return -ENODEV;
> > +}
> > +
> > +static void mshv_sint_remove(struct platform_device *pdev)
> > +{
> > +}
> > +#endif
> > +
> > +static const __maybe_unused struct acpi_device_id mshv_sint_device_ids[] = {
> > +	{"MSFT1003", 0},
> > +	{"", 0},
> > +};
> > +
> > +static struct platform_driver mshv_sint_drv = {
> > +	.probe = mshv_sint_probe,
> > +	.remove = mshv_sint_remove,
> > +	.driver = {
> > +		.name = "mshv_sint",
> > +		.acpi_match_table = ACPI_PTR(mshv_sint_device_ids),
> > +		.probe_type = PROBE_FORCE_SYNCHRONOUS,
> > +	},
> > +};
> > +
> > +static int __init mshv_sint_vector_init(void)
> > +{
> > +	int ret;
> > +
> > +	if (acpi_disabled)
> > +		return -ENODEV;
> > +
> > +	ret = platform_driver_register(&mshv_sint_drv);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (mshv_sint_vector == -1 || mshv_sint_irq == -1) {
> > +		platform_driver_unregister(&mshv_sint_drv);
> > +		return -ENODEV;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static void mshv_sint_vector_cleanup(void)
> > +{
> > +	platform_driver_unregister(&mshv_sint_drv);
> > +}
> > +#else /* HYPERVISOR_CALLBACK_VECTOR */
> > +static int __init mshv_sint_vector_init(void)
> > +{
> > +	mshv_sint_vector = HYPERVISOR_CALLBACK_VECTOR;
> > +	return 0;
> > +}
> > +
> > +static void mshv_sint_vector_cleanup(void)
> > +{
> > +}
> > +#endif /* HYPERVISOR_CALLBACK_VECTOR */
> > +
> >  int __init mshv_synic_init(struct device *dev)
> >  {
> >  	int ret = 0;
> >  
> > +	ret = mshv_sint_vector_init();
> > +	if (ret) {
> > +		dev_err(dev, "Failed to get MSHV SINT vector: %i\n", ret);
> > +		return ret;
> > +	}
> > +
> >  	synic_pages = alloc_percpu(struct hv_synic_pages);
> >  	if (!synic_pages) {
> >  		dev_err(dev, "Failed to allocate percpu synic page\n");
> > -		return -ENOMEM;
> > +		ret = -ENOMEM;
> > +		goto sint_vector_cleanup;
> >  	}
> >  
> >  	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mshv_synic",
> > @@ -712,6 +858,8 @@ int __init mshv_synic_init(struct device *dev)
> >  	cpuhp_remove_state(synic_cpuhp_online);
> >  free_synic_pages:
> >  	free_percpu(synic_pages);
> > +sint_vector_cleanup:
> > +	mshv_sint_vector_cleanup();
> >  	return ret;
> >  }
> >  
> > @@ -721,4 +869,5 @@ void mshv_synic_cleanup(void)
> >  		unregister_reboot_notifier(&mshv_synic_reboot_nb);
> >  	cpuhp_remove_state(synic_cpuhp_online);
> >  	free_percpu(synic_pages);
> > +	mshv_sint_vector_cleanup();
> >  }
> > -- 
> > 2.34.1
> >