git: f750dce972ef - main - x86/xen: fix accounted interrupt time

The branch main has been updated by royger:

URL: https://cgit.FreeBSD.org/src/commit/?id=f750dce972efaea614aa6d03ecdb24aa962a38a4

commit f750dce972efaea614aa6d03ecdb24aa962a38a4
Author:     Roger Pau Monné <royger@FreeBSD.org>
AuthorDate: 2024-03-05 13:15:03 +0000
Commit:     Roger Pau Monné <royger@FreeBSD.org>
CommitDate: 2024-04-16 07:06:33 +0000

    x86/xen: fix accounted interrupt time
    
    The current addition to the interrupt nesting level in
    xen_arch_intr_handle_upcall() needs to be compensated in
    xen_intr_handle_upcall(), otherwise interrupts dispatched by the upcall handler
    end up seeing a td_intr_nesting_level of 2 or more, which makes them assume
    there's been an interrupt nesting.
    
    Such extra interrupt nesting count lead to statclock() reporting idle time as
    interrupt, as the call from interrupt context will always be seen as a nested
    one (td->td_intr_nesting_level >= 2) due to the nesting count increase done by
    both xen_arch_intr_handle_upcall() and intr_execute_handlers().
    
    Fix this by adjusting the nested interrupt count before dispatching interrupts
    from xen_intr_handle_upcall().
    
    PR: 277231
    Reported by: Matthew Grooms <mgrooms@shrew.net>
    Fixes: af610cabf1f4 ('xen/intr: adjust xen_intr_handle_upcall() to match driver filter')
    Sponsored by: Cloud Software Group
    Reviewed by: Elliott Mitchell <ehem+freebsd@m5p.com>
---
 sys/dev/xen/bus/xen_intr.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/sys/dev/xen/bus/xen_intr.c b/sys/dev/xen/bus/xen_intr.c
index 609f31b5418a..bfe080b16f03 100644
--- a/sys/dev/xen/bus/xen_intr.c
+++ b/sys/dev/xen/bus/xen_intr.c
@@ -341,7 +341,7 @@ xen_intr_active_ports(const struct xen_intr_pcpu_data *const pcpu,
 /**
  * Interrupt handler for processing all Xen event channel events.
  * 
- * \param trap_frame  The trap frame context for the current interrupt.
+ * \param unused
  */
 int
 xen_intr_handle_upcall(void *unused __unused)
@@ -354,6 +354,15 @@ xen_intr_handle_upcall(void *unused __unused)
 	struct xen_intr_pcpu_data *pc;
 	u_long l1, l2;
 
+	/*
+	 * The upcall handler is an interrupt handler itself (that calls other
+	 * interrupt handlers), hence the caller has the responsibility to
+	 * increase td_intr_nesting_level ahead of dispatching the upcall
+	 * handler.
+	 */
+	KASSERT(curthread->td_intr_nesting_level > 0,
+	        ("Unexpected thread context"));
+
 	/* We must remain on the same vCPU during this function */
 	CRITICAL_ASSERT(curthread);
 
@@ -417,7 +426,17 @@ xen_intr_handle_upcall(void *unused __unused)
 				("Received unexpected event on vCPU#%u, event bound to vCPU#%u",
 				PCPU_GET(cpuid), isrc->xi_cpu));
 
+			/*
+			 * Reduce interrupt nesting level ahead of calling the
+			 * per-arch interrupt dispatch helper.  This is
+			 * required because the per-arch dispatcher will also
+			 * increase td_intr_nesting_level, and then handlers
+			 * would wrongly see td_intr_nesting_level = 2 when
+			 * there's no nesting at all.
+			 */
+			curthread->td_intr_nesting_level--;
 			xen_arch_intr_execute_handlers(isrc, trap_frame);
+			curthread->td_intr_nesting_level++;
 
 			/*
 			 * If this is the final port processed,