Re: IOCTL_PRIVCMD_MMAP

[Jed Davis <jdev%panix.com@localhost>]

Jed Davis <jdev%panix.com@localhost> writes:

> patch to xend; in both cases, with my change to IOCTL_PRIVCMD_MMAP,
> the panic is replaced by xend dying with:
>
>   xen.lowlevel.xu.PortError: Failed to map domain control interface
>
> At one point I noticed that one of the xpq_update_foreign calls in
> pmap_remap_pages was failing when this happens; I'll look into that
> some more.

It's failing because the foreign domain no longer exists, but xend
isn't aware of that and tries to map its control interface anyway.  I
have here a patch that rolls back the increment to the PTP's
wire_count if the update fails, and that avoids the panic without
needing to lock the remapped memory:

Index: sys/arch/xen/i386/pmap.c
===================================================================
RCS file: /cvsroot/src/sys/arch/xen/i386/pmap.c,v
retrieving revision 1.8.2.3
diff -u -p -r1.8.2.3 pmap.c
--- sys/arch/xen/i386/pmap.c    6 Jun 2005 12:16:10 -0000       1.8.2.3
+++ sys/arch/xen/i386/pmap.c    30 Aug 2005 01:39:13 -0000
@@ -4135,7 +4135,9 @@ pmap_remap_pages(pmap, va, pa, npages, f
        struct vm_page_md *mdpg;
        struct pv_head *old_pvh;
        struct pv_entry *pve = NULL; /* XXX gcc */
-       int error;
+       int error, dptpwire;
+
+       dptpwire = 0;
 
        XENPRINTK(("pmap_remap_pages(%p, %p, %p, %d, %08x, %d)\n",
            pmap, (void *)va, (void *)pa, npages, flags, dom));
@@ -4301,14 +4305,23 @@ pmap_remap_pages(pmap, va, pa, npages, f
        } else {
                pmap->pm_stats.resident_count++;
                pmap->pm_stats.wired_count++;
-               if (ptp)
+               if (ptp) {
+                       dptpwire = 1;
                        ptp->wire_count++;
+               }
        }
 
        //printf("pmap initial setup");
        maptp = (pt_entry_t *)vtomach((vaddr_t)&ptes[x86_btop(va)]);
        error = xpq_update_foreign(maptp, npte, dom);
-
+       if (error) {
+               printf("pmap_remap_pages: xpq_update_foreign failed; %d\n",
+                      dptpwire);
+               ptp->wire_count -= dptpwire;
+               /* XXX fix other stats? */
+               goto out;
+       }
+       
 shootdown_test:
        /* Update page attributes if needed */
        if ((opte & (PG_V | PG_U)) == (PG_V | PG_U)) {


-- 
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((lambda (r) ((C C) (lambda (s) (r (lambda l (apply (s s) l))))))  (lambda
(f) (lambda (l) (if (null? l) C (lambda (k) (display (car l)) ((f (cdr l))
(C k)))))))    '((#\J #\d #\D #\v #\s) (#\e #\space #\a #\i #\newline)))))