[src/trunk]: src/sys/arch/xen/x86 xen_intr.c: Use kpreempt_disable/enable aro...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ff17715d5fba
branches:  trunk
changeset: 373709:ff17715d5fba
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sat Feb 25 00:32:13 2023 +0000

description:
xen_intr.c: Use kpreempt_disable/enable around access to curcpu().

curcpu() is not otherwise guaranteed to be stable at these points.

While here, nix nonsensical membars.  This need only be synchronized
with interrupts on the same CPU.

Proposed on port-xen:
https://mail-index.netbsd.org/port-xen/2022/07/13/msg010250.html

XXX pullup-8 (in __sti/__cli, __save/restore_flags in include/xen.h)
XXX pullup-9
XXX pullup-10

diffstat:

 sys/arch/xen/x86/xen_intr.c |  40 ++++++++++++++++++++++++++++------------
 1 files changed, 28 insertions(+), 12 deletions(-)

diffs (85 lines):

diff -r fc576fa9a529 -r ff17715d5fba sys/arch/xen/x86/xen_intr.c
--- a/sys/arch/xen/x86/xen_intr.c       Sat Feb 25 00:31:40 2023 +0000
+++ b/sys/arch/xen/x86/xen_intr.c       Sat Feb 25 00:32:13 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: xen_intr.c,v 1.30 2022/05/24 14:00:23 bouyer Exp $     */
+/*     $NetBSD: xen_intr.c,v 1.31 2023/02/25 00:32:13 riastradh Exp $  */
 
 /*-
  * Copyright (c) 1998, 2001 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: xen_intr.c,v 1.30 2022/05/24 14:00:23 bouyer Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xen_intr.c,v 1.31 2023/02/25 00:32:13 riastradh Exp $");
 
 #include "opt_multiprocessor.h"
 #include "opt_pci.h"
@@ -83,19 +83,28 @@
 void
 x86_disable_intr(void)
 {
+
+       kpreempt_disable();
        curcpu()->ci_vcpu->evtchn_upcall_mask = 1;
-       x86_lfence();
+       kpreempt_enable();
+
+       __insn_barrier();
 }
 
 void
 x86_enable_intr(void)
 {
-       volatile struct vcpu_info *_vci = curcpu()->ci_vcpu;
+       struct cpu_info *ci;
+
        __insn_barrier();
-       _vci->evtchn_upcall_mask = 0;
-       x86_lfence(); /* unmask then check (avoid races) */
-       if (__predict_false(_vci->evtchn_upcall_pending))
+
+       kpreempt_disable();
+       ci = curcpu();
+       ci->ci_vcpu->evtchn_upcall_mask = 0;
+       __insn_barrier();
+       if (__predict_false(ci->ci_vcpu->evtchn_upcall_pending))
                hypervisor_force_callback();
+       kpreempt_enable();
 }
 
 #endif /* !XENPVHVM */
@@ -103,20 +112,27 @@
 u_long
 xen_read_psl(void)
 {
+       u_long psl;
 
-       return (curcpu()->ci_vcpu->evtchn_upcall_mask);
+       kpreempt_disable();
+       psl = curcpu()->ci_vcpu->evtchn_upcall_mask;
+       kpreempt_enable();
+
+       return psl;
 }
 
 void
 xen_write_psl(u_long psl)
 {
-       struct cpu_info *ci = curcpu();
+       struct cpu_info *ci;
 
+       kpreempt_disable();
+       ci = curcpu();
        ci->ci_vcpu->evtchn_upcall_mask = psl;
-       xen_rmb();
-       if (ci->ci_vcpu->evtchn_upcall_pending && psl == 0) {
+       __insn_barrier();
+       if (__predict_false(ci->ci_vcpu->evtchn_upcall_pending) && psl == 0)
                hypervisor_force_callback();
-       }
+       kpreempt_enable();
 }
 
 void *