Re: [PATCH v5 2/2] mshv: add arm64 support for doorbell & intercept SINTs

[Anirudh Rayabharam <anirudh@anirudhrb.com>]

On Mon, Feb 23, 2026 at 11:39:43AM -0800, Stanislav Kinsburskii wrote:
> On Mon, Feb 23, 2026 at 02:01:59PM +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 hypervisor exposes a synthetic register that can be read
> > to find the INTID that should be used for SINTs. This INTID is in the
> > PPI range.
> > 
> > To better unify the code paths, introduce mshv_sint_vector_init() that
> > either reads the synthetic register 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     | 120 +++++++++++++++++++++++++++++++++---
> >  include/hyperv/hvgdk_mini.h |   2 +
> >  2 files changed, 112 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/hv/mshv_synic.c b/drivers/hv/mshv_synic.c
> > index 074e37c48876..75ef2160b3e0 100644
> > --- a/drivers/hv/mshv_synic.c
> > +++ b/drivers/hv/mshv_synic.c
> > @@ -10,17 +10,22 @@
> >  #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 */
> > +static int mshv_sint_irq = -1; /* Linux IRQ for mshv_sint_vector */
> >  
> >  static u32 synic_event_ring_get_queued_port(u32 sint_index)
> >  {
> > @@ -442,9 +447,7 @@ void mshv_isr(void)
> >  		if (msg->header.message_flags.msg_pending)
> >  			hv_set_non_nested_msr(HV_MSR_EOM, 0);
> >  
> > -#ifdef HYPERVISOR_CALLBACK_VECTOR
> > -		add_interrupt_randomness(HYPERVISOR_CALLBACK_VECTOR);
> > -#endif
> > +		add_interrupt_randomness(mshv_sint_vector);
> >  	} else {
> >  		pr_warn_once("%s: unknown message type 0x%x\n", __func__,
> >  			     msg->header.message_type);
> > @@ -456,9 +459,7 @@ 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 +502,12 @@ static int mshv_synic_cpu_init(unsigned int cpu)
> >  
> >  	hv_set_non_nested_msr(HV_MSR_SIRBP, sirbp.as_uint64);
> >  
> > -#ifdef HYPERVISOR_CALLBACK_VECTOR
> > +	if (mshv_sint_irq != -1)
> > +		enable_percpu_irq(mshv_sint_irq, 0);
> > +
> >  	/* 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 +515,12 @@ 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 +575,9 @@ 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);
> >  
> > +	if (mshv_sint_irq != -1)
> > +		disable_percpu_irq(mshv_sint_irq);
> > +
> >  	/* Disable Synic's event ring page */
> >  	sirbp.as_uint64 = hv_get_non_nested_msr(HV_MSR_SIRBP);
> >  	sirbp.sirbp_enabled = false;
> > @@ -683,14 +688,106 @@ static struct notifier_block mshv_synic_reboot_nb = {
> >  	.notifier_call = mshv_synic_reboot_notify,
> >  };
> >  
> > +#ifndef HYPERVISOR_CALLBACK_VECTOR
> > +static DEFINE_PER_CPU(long, mshv_evt);
> > +
> > +static irqreturn_t mshv_percpu_isr(int irq, void *dev_id)
> > +{
> > +	mshv_isr();
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +#ifdef CONFIG_ACPI
> > +static int __init mshv_acpi_setup_sint_irq(void)
> > +{
> > +	return acpi_register_gsi(NULL, mshv_sint_vector, ACPI_EDGE_SENSITIVE,
> > +					ACPI_ACTIVE_HIGH);
> > +}
> > +
> > +static void mshv_acpi_cleanup_sint_irq(void)
> > +{
> > +	acpi_unregister_gsi(mshv_sint_vector);
> > +}
> > +#else
> > +static int __init mshv_acpi_setup_sint_irq(void)
> > +{
> > +	return -ENODEV;
> > +}
> > +
> > +static void mshv_acpi_cleanup_sint_irq(void)
> > +{
> > +}
> > +#endif
> > +
> > +static int __init mshv_sint_vector_init(void)
> > +{
> > +	int ret;
> > +	struct hv_register_assoc reg = {
> > +		.name = HV_ARM64_REGISTER_SINT_RESERVED_INTERRUPT_ID,
> > +	};
> > +	union hv_input_vtl input_vtl = { 0 };
> > +
> > +	if (acpi_disabled)
> > +		return -ENODEV;
> > +
> > +	ret = hv_call_get_vp_registers(HV_VP_INDEX_SELF, HV_PARTITION_ID_SELF,
> > +				1, input_vtl, &reg);
> > +	if (ret || !reg.value.reg64)
> > +		return -ENODEV;
> > +
> > +	mshv_sint_vector = reg.value.reg64;
> > +	ret = mshv_acpi_setup_sint_irq();
> > +	if (ret <= 0) {
> > +		pr_err("Failed to setup IRQ for MSHV SINT vector %d: %d\n",
> > +			mshv_sint_vector, ret);
> > +		goto out_fail;
> > +	}
> > +
> > +	mshv_sint_irq = ret;
> 
> nit: given that mshv_sint_irq can't be zero, the logic can be simplified by
> using 0 instead of -1.
> 
> 
> 
> > +
> > +	ret = request_percpu_irq(mshv_sint_irq, mshv_percpu_isr, "MSHV",
> > +		&mshv_evt);
> > +	if (ret)
> > +		goto out_unregister;
> > +
> > +	return 0;
> > +
> > +out_unregister:
> > +	mshv_acpi_cleanup_sint_irq();
> > +out_fail:
> > +	return ret;
> > +}
> > +
> > +static void mshv_sint_vector_cleanup(void)
> > +{
> > +	free_percpu_irq(mshv_sint_irq, &mshv_evt);
> > +	mshv_acpi_cleanup_sint_irq();
> > +}
> > +#else /* !HYPERVISOR_CALLBACK_VECTOR */
> > +static int __init mshv_sint_vector_init(void)
> 
> nit: `init` is usually paired with `exit` or `fini`, so maybe `cleanup` can be
> renamed to `exit` as well for better consistency?
> 
> Reviewed-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>

Thanks! I'll fix the naming inconsistencies and also pickup your
Reviewed-by in v6.

Anirudh.

> 
> > +{
> > +	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)
> > +		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",
> > @@ -713,6 +810,8 @@ 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 +820,5 @@ 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();
> >  }
> > diff --git a/include/hyperv/hvgdk_mini.h b/include/hyperv/hvgdk_mini.h
> > index 30fbbde81c5c..7676f78e0766 100644
> > --- a/include/hyperv/hvgdk_mini.h
> > +++ b/include/hyperv/hvgdk_mini.h
> > @@ -1117,6 +1117,8 @@ enum hv_register_name {
> >  	HV_X64_REGISTER_MSR_MTRR_FIX4KF8000	= 0x0008007A,
> >  
> >  	HV_X64_REGISTER_REG_PAGE	= 0x0009001C,
> > +#elif defined(CONFIG_ARM64)
> > +	HV_ARM64_REGISTER_SINT_RESERVED_INTERRUPT_ID	= 0x00070001,
> >  #endif
> >  };
> >  
> > -- 
> > 2.34.1
> >