x86: hyperv: Add mshv_handler() irq handler and setup function

Add mshv_handler() to process messages related to managing guest
partitions such as intercepts, doorbells, and scheduling messages.

In a (non-nested) root partition, the same interrupt vector is shared
between the vmbus and mshv_root drivers.

Introduce a stub for mshv_handler() and call it in
sysvec_hyperv_callback alongside vmbus_handler().

Even though both handlers will be called for every Hyper-V interrupt,
the messages for each driver are delivered to different offsets
within the SYNIC message page, so they won't step on each other.

Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Wei Liu <wei.liu@kernel.org>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Reviewed-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Link: https://lore.kernel.org/r/1741980536-3865-9-git-send-email-nunodasneves@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <1741980536-3865-9-git-send-email-nunodasneves@linux.microsoft.com>

arch/x86/kernel/cpu/mshyperv.c

@@ -107,6 +107,7 @@ void hv_set_msr(unsigned int reg, u64 value)
 }
 EXPORT_SYMBOL_GPL(hv_set_msr);
 
+static void (*mshv_handler)(void);
 static void (*vmbus_handler)(void);
 static void (*hv_stimer0_handler)(void);
 static void (*hv_kexec_handler)(void);
@@ -117,6 +118,9 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
 	struct pt_regs *old_regs = set_irq_regs(regs);
 
 	inc_irq_stat(irq_hv_callback_count);
+	if (mshv_handler)
+		mshv_handler();
+
 	if (vmbus_handler)
 		vmbus_handler();
 
@@ -126,6 +130,11 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_hyperv_callback)
 	set_irq_regs(old_regs);
 }
 
+void hv_setup_mshv_handler(void (*handler)(void))
+{
+	mshv_handler = handler;
+}
+
 void hv_setup_vmbus_handler(void (*handler)(void))
 {
 	vmbus_handler = handler;

drivers/hv/hv_common.c

@@ -680,6 +680,11 @@ void __weak hv_remove_vmbus_handler(void)
 }
 EXPORT_SYMBOL_GPL(hv_remove_vmbus_handler);
 
+void __weak hv_setup_mshv_handler(void (*handler)(void))
+{
+}
+EXPORT_SYMBOL_GPL(hv_setup_mshv_handler);
+
 void __weak hv_setup_kexec_handler(void (*handler)(void))
 {
 }

include/asm-generic/mshyperv.h

@@ -208,6 +208,7 @@ void hv_setup_kexec_handler(void (*handler)(void));
 void hv_remove_kexec_handler(void);
 void hv_setup_crash_handler(void (*handler)(struct pt_regs *regs));
 void hv_remove_crash_handler(void);
+void hv_setup_mshv_handler(void (*handler)(void));
 
 extern int vmbus_interrupt;
 extern int vmbus_irq;