Re: [Xen-ia64-devel] Patch for PV-on-HVM for IPF

[DOI Tsunehisa <Doi.Tsunehisa@xxxxxxxxxxxxxx>]

Sorry, I forgot to attach the patch.

DOI Tsunehisa wrote:
> Hi all,
> 
>   Currently, we are testing PV-on-HVM driver for IPF. so, we found
> a problem that hypervisor crashes during VT-i domain destruction
> with PV-on-HVM driver.
> 
>   The procedure to reproduce this problem are:
> 
>    * Create a VT-i domain.
>      [dom0]# xm create -f hvm.conf
>    * Insert modules for PV-on-HVM on the domain.
>      [domvti]# insmod xen-platform-pci.ko
>      [domvti]# insmod xenbus.ko
>      [domvti]# insmod xen-vbd.ko
>      [domvti]# insmod xen-vnif.ko
>    * Activate VNIF network interface.
>      [dom0]# xm network-attach <domid> eth1
>      [domvti]# ifconfig eth1 up
>    * Destruct the domain
>      [dom0]# xm destroy <domid>
>      ..... hypervisor crash  ....
> 
>   We were investigating the hypervisor crash mechanism, thus we found
> a reason of it.
> 
>   * VNIF of PV-on-HVM uses gnttab_copy() function.
>     - it's used for copy-method of VNIF backend.
>     - it needs to refer p2m table.
>   * gnttab_copy() function may be called during the domain destruction.
>     - it's called by dom0 VNIF backend.
>   * Hypervisor invalidates p2m table at first during the destruction.
>     - gnttab_copy() won't be able to refer p2m table, thus it occurs
>       hypervisor crash.
>     - In x86 code, p2m table invalidation is delayed at last phase of
>       domain destruction.
>       => but we don't like it. it seems that p2m table exists after
>          memory relinquised.
> 
>   So, I'll post a patch to avoid hypervisor crash.
> 
>    * pv-avoid-crash.patch
>      + modify p2m table converter (gmfn_to_mfn_foreign())
>        - return INVALID_MFN during VT-i domain destruction
> 
>   We tested that the problem is solved.
> 
> Thanks,
> - Tsunehisa Doi
> 
> 
> _______________________________________________
> Xen-ia64-devel mailing list
> Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-ia64-devel

# HG changeset patch
# User Doi.Tsunehisa@xxxxxxxxxxxxxx
# Node ID 354f40902eb9e3f92fdf8b5e9268052cd955230b
# Parent  f34e37d0742d80ccfefd017a91f93310ebc2dfe8
Modify p2m converter to avoid hypervisor crash
during destruction of VT-i domain with PV-on-HVM.

Signed-off-by: Tsunehisa Doi <Doi.Tsunehisa@xxxxxxxxxxxxxx>
Signed-off-by: Tomonari Horikoshi <t.horikoshi@xxxxxxxxxxxxxx>

diff -r f34e37d0742d -r 354f40902eb9 xen/arch/ia64/xen/mm.c
--- a/xen/arch/ia64/xen/mm.c    Tue Sep 26 19:11:33 2006 -0600
+++ b/xen/arch/ia64/xen/mm.c    Wed Sep 27 17:24:58 2006 +0900
@@ -396,6 +396,12 @@ gmfn_to_mfn_foreign(struct domain *d, un
 {
        unsigned long pte;
 
+       // This function may be called from __gnttab_copy()
+       // during destruction of VT-i domain with PV-on-HVM driver.
+       if (unlikely(d->arch.mm.pgd == NULL)) {
+               if (VMX_DOMAIN(d->vcpu[0]))
+                       return INVALID_MFN;
+       }
        pte = lookup_domain_mpa(d,gpfn << PAGE_SHIFT, NULL);
        if (!pte) {
                panic("gmfn_to_mfn_foreign: bad gpfn. spinning...\n");

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