linux-kernel - [PATCH] xen: Allow platform PCI interrupt to be shared

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Message-ID: <f9a29a68d05668a3636dd09acd94d970269eaec6.camel@infradead.org>
Date:   Wed, 18 Jan 2023 12:22:38 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Paul Durrant <paul@....org>
Subject: [PATCH] xen: Allow platform PCI interrupt to be shared

From: David Woodhouse <dwmw@...zon.co.uk>

When we don't use the per-CPU vector callback, we ask Xen to deliver event
channel interrupts as INTx on the PCI platform device. As such, it can be
shared with INTx on other PCI devices.

Set IRQF_SHARED, and make it return IRQ_HANDLED or IRQ_NONE according to
whether the evtchn_upcall_pending flag was actually set. Now I can share
the interrupt:

 11:         82          0   IO-APIC  11-fasteoi   xen-platform-pci, ens4

Drop the IRQF_TRIGGER_RISING. It has no effect when the IRQ is shared,
and besides, the only effect it was having even beforehand was to trigger
a debug message in both I/OAPIC and legacy PIC cases:

[    0.915441] genirq: No set_type function for IRQ 11 (IO-APIC)
[    0.951939] genirq: No set_type function for IRQ 11 (XT-PIC)

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
What does xen_evtchn_do_upcall() exist for? Can we delete it? I don't
see it being called anywhere.

 drivers/xen/events/events_base.c | 9 ++++++---
 drivers/xen/platform-pci.c       | 5 ++---
 include/xen/events.h             | 2 +-
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index c443f04aaad7..c7715f8bd452 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -1710,9 +1710,10 @@ void handle_irq_for_port(evtchn_port_t port, struct evtchn_loop_ctrl *ctrl)
 	generic_handle_irq(irq);
 }
 
-static void __xen_evtchn_do_upcall(void)
+static int __xen_evtchn_do_upcall(void)
 {
 	struct vcpu_info *vcpu_info = __this_cpu_read(xen_vcpu);
+	int ret = vcpu_info->evtchn_upcall_pending ? IRQ_HANDLED : IRQ_NONE;
 	int cpu = smp_processor_id();
 	struct evtchn_loop_ctrl ctrl = { 0 };
 
@@ -1737,6 +1738,8 @@ static void __xen_evtchn_do_upcall(void)
 	 * above.
 	 */
 	__this_cpu_inc(irq_epoch);
+
+	return ret;
 }
 
 void xen_evtchn_do_upcall(struct pt_regs *regs)
@@ -1751,9 +1754,9 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
 	set_irq_regs(old_regs);
 }
 
-void xen_hvm_evtchn_do_upcall(void)
+int xen_hvm_evtchn_do_upcall(void)
 {
-	__xen_evtchn_do_upcall();
+	return __xen_evtchn_do_upcall();
 }
 EXPORT_SYMBOL_GPL(xen_hvm_evtchn_do_upcall);
 
diff --git a/drivers/xen/platform-pci.c b/drivers/xen/platform-pci.c
index cd07e3fed0fa..fcc819131572 100644
--- a/drivers/xen/platform-pci.c
+++ b/drivers/xen/platform-pci.c
@@ -64,14 +64,13 @@ static uint64_t get_callback_via(struct pci_dev *pdev)
 
 static irqreturn_t do_hvm_evtchn_intr(int irq, void *dev_id)
 {
-	xen_hvm_evtchn_do_upcall();
-	return IRQ_HANDLED;
+	return xen_hvm_evtchn_do_upcall();
 }
 
 static int xen_allocate_irq(struct pci_dev *pdev)
 {
 	return request_irq(pdev->irq, do_hvm_evtchn_intr,
-			IRQF_NOBALANCING | IRQF_TRIGGER_RISING,
+			IRQF_NOBALANCING | IRQF_SHARED,
 			"xen-platform-pci", pdev);
 }
 
diff --git a/include/xen/events.h b/include/xen/events.h
index 344081e71584..44c2855c76d1 100644
--- a/include/xen/events.h
+++ b/include/xen/events.h
@@ -107,7 +107,7 @@ evtchn_port_t evtchn_from_irq(unsigned irq);
 
 int xen_set_callback_via(uint64_t via);
 void xen_evtchn_do_upcall(struct pt_regs *regs);
-void xen_hvm_evtchn_do_upcall(void);
+int xen_hvm_evtchn_do_upcall(void);
 
 /* Bind a pirq for a physical interrupt to an irq. */
 int xen_bind_pirq_gsi_to_irq(unsigned gsi,
-- 
2.39.0



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