[src/trunk]: src/sys/arch/powerpc/ibm4xx Use uvm_km_alloc(9) with UVM_KMF_NOW...

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

details:   https://anonhg.NetBSD.org/src/rev/fbc2006823ff
branches:  trunk
changeset: 378498:fbc2006823ff
user:      rin <rin%NetBSD.org@localhost>
date:      Thu Apr 15 00:00:46 2021 +0000

description:
Use uvm_km_alloc(9) with UVM_KMF_NOWAIT flag in pte_enter(), in order not to
sleep in pmap_enter(9) and pmap_kenter_pa(9), which can result in dead lock.

In most cases, pmap_enter(9) is used with PMAP_CANFAIL flag. In this case,
if pte_enter() fails due to uvm_km_alloc(9), we can safely return ENOMEM.
UVM layer will take care of it.

uvm_km_alloc(9) fails for pmap_enter(9) without PMAP_CANFAIL or for
pmap_kenter_pa(9), we have no choice but to panic there.

However, my testbeds for 403 and 405 survive more than a week at least
without hitting this panic.

diffstat:

 sys/arch/powerpc/ibm4xx/pmap.c |  30 ++++++++++++++++++++----------
 1 files changed, 20 insertions(+), 10 deletions(-)

diffs (80 lines):

diff -r 46781b75d8de -r fbc2006823ff sys/arch/powerpc/ibm4xx/pmap.c
--- a/sys/arch/powerpc/ibm4xx/pmap.c    Wed Apr 14 23:45:11 2021 +0000
+++ b/sys/arch/powerpc/ibm4xx/pmap.c    Thu Apr 15 00:00:46 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: pmap.c,v 1.97 2021/04/14 23:45:11 rin Exp $    */
+/*     $NetBSD: pmap.c,v 1.98 2021/04/15 00:00:46 rin Exp $    */
 
 /*
  * Copyright 2001 Wasabi Systems, Inc.
@@ -67,7 +67,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.97 2021/04/14 23:45:11 rin Exp $");
+__KERNEL_RCSID(0, "$NetBSD: pmap.c,v 1.98 2021/04/15 00:00:46 rin Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ddb.h"
@@ -236,11 +236,15 @@ pte_enter(struct pmap *pm, vaddr_t va, u
        if (!pm->pm_ptbl[seg]) {
                /* Don't allocate a page to clear a non-existent mapping. */
                if (!pte)
+                       return 1;
+
+               vaddr_t km = uvm_km_alloc(kernel_map, PAGE_SIZE, 0,
+                   UVM_KMF_WIRED | UVM_KMF_ZERO | UVM_KMF_NOWAIT);
+
+               if (__predict_false(km == 0))
                        return 0;
-               /* Allocate a page XXXX this will sleep! */
-               pm->pm_ptbl[seg] =
-                   (uint *)uvm_km_alloc(kernel_map, PAGE_SIZE, 0,
-                   UVM_KMF_WIRED | UVM_KMF_ZERO);
+
+               pm->pm_ptbl[seg] = (u_int *)km;
        }
        oldpte = pm->pm_ptbl[seg][ptn];
        pm->pm_ptbl[seg][ptn] = pte;
@@ -862,7 +866,7 @@ pmap_enter(struct pmap *pm, vaddr_t va, 
 
                if (!pmap_enter_pv(pm, va, pa, flags)) {
                        /* Could not enter pv on a managed page */
-                       return 1;
+                       return ENOMEM;
                }
 
                /* Now set attributes. */
@@ -880,7 +884,12 @@ pmap_enter(struct pmap *pm, vaddr_t va, 
        s = splvm();
 
        /* Insert page into page table. */
-       pte_enter(pm, va, tte);
+       if (__predict_false(!pte_enter(pm, va, tte))) {
+               if (__predict_false((flags & PMAP_CANFAIL) == 0))
+                       panic("%s: pte_enter", __func__);
+               splx(s);
+               return ENOMEM;
+       }
 
        /* If this is a real fault, enter it in the tlb */
        if (tte && ((flags & PMAP_WIRED) == 0)) {
@@ -969,7 +978,8 @@ pmap_kenter_pa(vaddr_t va, paddr_t pa, v
        s = splvm();
 
        /* Insert page into page table. */
-       pte_enter(pm, va, tte);
+       if (__predict_false(!pte_enter(pm, va, tte)))
+               panic("%s: pte_enter", __func__);
        splx(s);
 }
 
@@ -978,7 +988,7 @@ pmap_kremove(vaddr_t va, vsize_t len)
 {
 
        while (len > 0) {
-               pte_enter(pmap_kernel(), va, 0);
+               (void)pte_enter(pmap_kernel(), va, 0);  /* never fail */
                va += PAGE_SIZE;
                len -= PAGE_SIZE;
        }