Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux Dom0

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

The following reply was made to PR port-xen/47057; it has been noted by GNATS.

From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau%citrix.com@localhost>
Cc: "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%NetBSD.org@localhost>,
        "port-xen-maintainer%netbsd.org@localhost" 
<port-xen-maintainer%NetBSD.org@localhost>,
        "gnats-admin%netbsd.org@localhost" <gnats-admin%NetBSD.org@localhost>,
        "netbsd-bugs%netbsd.org@localhost" <netbsd-bugs%NetBSD.org@localhost>,
        "royger%netbsd.org@localhost" <royger%NetBSD.org@localhost>
Subject: Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux
 Dom0
Date: Sun, 21 Oct 2012 13:29:10 +0200

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 On Sat, Oct 20, 2012 at 08:34:16PM +0200, Roger Pau Monné wrote:
 > I'm sorry to say that the patch didn't seem to help, here is another
 > output with your patch applied. It seems like prod and cons gets
 > overwritten with random data.
 
 OK, here's another patch, which also checks that the mapping doesn't
 change. But I wonder is the corruption occurs on the NetBSD side.
 Could you also add some debugging code on the other side ?
 
 -- 
 Manuel Bouyer <bouyer%antioche.eu.org@localhost>
      NetBSD: 26 ans d'experience feront toujours la difference
 --
 
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 Index: xenbus_comms.c
 ===================================================================
 RCS file: /cvsroot/src/sys/arch/xen/xenbus/xenbus_comms.c,v
 retrieving revision 1.14
 diff -u -p -u -r1.14 xenbus_comms.c
 --- xenbus_comms.c     20 Sep 2011 00:12:24 -0000      1.14
 +++ xenbus_comms.c     21 Oct 2012 11:26:23 -0000
 @@ -37,6 +37,7 @@ __KERNEL_RCSID(0, "$NetBSD: xenbus_comms
  #include <sys/param.h>
  #include <sys/proc.h>
  #include <sys/systm.h>
 +#include <uvm/uvm_extern.h>
  
  #include <xen/xen.h>  /* for xendomain_is_dom0() */
  #include <xen/hypervisor.h>
 @@ -121,7 +122,10 @@ xb_write(const void *data, unsigned len)
        while (len != 0) {
                void *dst;
                unsigned int avail;
 +              paddr_t pa;
  
 +              KASSERT(pmap_extract_ma(pmap_kernel(), (vaddr_t)intf, &pa));
 +              KASSERT(pa == (xen_start_info.store_mfn << PAGE_SHIFT));
                while ((intf->req_prod - intf->req_cons) == XENSTORE_RING_SIZE) 
{
                        XENPRINTF(("xb_write tsleep\n"));
                        tsleep(&xenstore_interface, PRIBIO, "wrst", 0);
 @@ -142,6 +146,10 @@ xb_write(const void *data, unsigned len)
                        continue;
                if (avail > len)
                        avail = len;
 +              pmap_kenter_ma((vaddr_t)intf,
 +                  xen_start_info.store_mfn << PAGE_SHIFT,
 +                  VM_PROT_READ | VM_PROT_WRITE, 0);
 +              pmap_update(pmap_kernel());
  
                memcpy(dst, data, avail);
                data = (const char *)data + avail;
 @@ -151,6 +159,10 @@ xb_write(const void *data, unsigned len)
                xen_rmb();
                intf->req_prod += avail;
                xen_rmb();
 +              pmap_protect(pmap_kernel(), (vaddr_t)intf,
 +                  (vaddr_t)intf + PAGE_SIZE,
 +                  VM_PROT_READ);
 +              pmap_update(pmap_kernel());
  
                hypervisor_notify_via_evtchn(xen_start_info.store_evtchn);
        }
 @@ -170,6 +182,10 @@ xb_read(void *data, unsigned len)
        while (len != 0) {
                unsigned int avail;
                const char *src;
 +              paddr_t pa;
 +
 +              KASSERT(pmap_extract_ma(pmap_kernel(), (vaddr_t)intf, &pa));
 +              KASSERT(pa == (xen_start_info.store_mfn << PAGE_SHIFT));
  
                while (intf->rsp_cons == intf->rsp_prod)
                        tsleep(&xenstore_interface, PRIBIO, "rdst", 0);
 @@ -198,9 +214,17 @@ xb_read(void *data, unsigned len)
                len -= avail;
  
                /* Other side must not see free space until we've copied out */
 +              pmap_kenter_ma((vaddr_t)intf,
 +                  xen_start_info.store_mfn << PAGE_SHIFT,
 +                  VM_PROT_READ | VM_PROT_WRITE, 0);
 +              pmap_update(pmap_kernel());
                xen_rmb();
                intf->rsp_cons += avail;
                xen_rmb();
 +              pmap_protect(pmap_kernel(), (vaddr_t)intf,
 +                  (vaddr_t)intf + PAGE_SIZE,
 +                  VM_PROT_READ);
 +              pmap_update(pmap_kernel());
  
                XENPRINTF(("Finished read of %i bytes (%i to go)\n",
                    avail, len));
 
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