| Message ID | 20170804022025.25293-4-blackskygg@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Aug 04, 2017 at 10:20:24AM +0800, Zhongze Liu wrote: > Two checks in the p2m code forbids sharing physical pages among DomU's by using > xc_add_to_physmap_batch with XENMAPSPACE_gmfn_foreign. Just simply remove them > in this RFC patch to ask for suggestions on how to properly handle this. > > This is for the proposal "Allow setting up shared memory areas between VMs > from xl config file" (see [1]). > > [1] https://lists.xenproject.org/archives/html/xen-devel/2017-07/msg03047.html > > Signed-off-by: Zhongze Liu <blackskygg@gmail.com> > --- > Cc: George Dunlap <george.dunlap@eu.citrix.com> > Cc: Jan Beulich <jbeulich@suse.com> > Cc: Andrew Cooper <andrew.cooper3@citrix.com> > Cc: Stefano Stabellini <sstabellini@kernel.org> > Cc: Julien Grall <julien.grall@arm.com> > Cc: xen-devel@lists.xen.org > --- > xen/arch/x86/mm/p2m.c | 20 +++++++++++++++----- > 1 file changed, 15 insertions(+), 5 deletions(-) > > diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c > index e8a57d118c..3ee4c14ed4 100644 > --- a/xen/arch/x86/mm/p2m.c > +++ b/xen/arch/x86/mm/p2m.c > @@ -2531,8 +2531,13 @@ int p2m_add_foreign(struct domain *tdom, unsigned long fgfn, > * hvm fixme: until support is added to p2m teardown code to cleanup any > * foreign entries, limit this to hardware domain only. This HVM fixme needs to be fixed before the check can go away. This is going to be a non-trivial project, but it is going to be useful in its own right.
Hi Wei, Yes, indeed. Before the teardown is implemented, even if I simply remove the first check, when I try to destroy the master domain, the domain will become a zombie, because the refcount of the shared pages won't be correctly decreased on slave destruction. I don't know why this hasn't been done, so I'm separating this patch out to serve as a place to discuss this problem. For this GSoC project, I would also ask if there is any temporary workaround. While waiting for any further suggestions and answers, I'll continue to work on the ARM side. Cheers, Zhongze Liu 2017-08-04 21:27 GMT+08:00 Wei Liu <wei.liu2@citrix.com>: > On Fri, Aug 04, 2017 at 10:20:24AM +0800, Zhongze Liu wrote: >> Two checks in the p2m code forbids sharing physical pages among DomU's by using >> xc_add_to_physmap_batch with XENMAPSPACE_gmfn_foreign. Just simply remove them >> in this RFC patch to ask for suggestions on how to properly handle this. >> >> This is for the proposal "Allow setting up shared memory areas between VMs >> from xl config file" (see [1]). >> >> [1] https://lists.xenproject.org/archives/html/xen-devel/2017-07/msg03047.html >> >> Signed-off-by: Zhongze Liu <blackskygg@gmail.com> >> --- >> Cc: George Dunlap <george.dunlap@eu.citrix.com> >> Cc: Jan Beulich <jbeulich@suse.com> >> Cc: Andrew Cooper <andrew.cooper3@citrix.com> >> Cc: Stefano Stabellini <sstabellini@kernel.org> >> Cc: Julien Grall <julien.grall@arm.com> >> Cc: xen-devel@lists.xen.org >> --- >> xen/arch/x86/mm/p2m.c | 20 +++++++++++++++----- >> 1 file changed, 15 insertions(+), 5 deletions(-) >> >> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c >> index e8a57d118c..3ee4c14ed4 100644 >> --- a/xen/arch/x86/mm/p2m.c >> +++ b/xen/arch/x86/mm/p2m.c >> @@ -2531,8 +2531,13 @@ int p2m_add_foreign(struct domain *tdom, unsigned long fgfn, >> * hvm fixme: until support is added to p2m teardown code to cleanup any >> * foreign entries, limit this to hardware domain only. > > This HVM fixme needs to be fixed before the check can go away. This is > going to be a non-trivial project, but it is going to be useful in its > own right.
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c index e8a57d118c..3ee4c14ed4 100644 --- a/xen/arch/x86/mm/p2m.c +++ b/xen/arch/x86/mm/p2m.c @@ -2531,8 +2531,13 @@ int p2m_add_foreign(struct domain *tdom, unsigned long fgfn, * hvm fixme: until support is added to p2m teardown code to cleanup any * foreign entries, limit this to hardware domain only. */ - if ( !is_hardware_domain(tdom) ) - return -EPERM; + /* The following check prevents us from doing a XENMEM_add_to_physmap + * between two domU's. Asking for suggestions on how to remove or + * work around it. + * + * if ( !is_hardware_domain(tdom) ) + * return -EPERM; + */ if ( foreigndom == DOMID_XEN ) fdom = rcu_lock_domain(dom_xen); @@ -2545,9 +2550,14 @@ int p2m_add_foreign(struct domain *tdom, unsigned long fgfn, if ( tdom == fdom ) goto out; - rc = xsm_map_gmfn_foreign(XSM_TARGET, tdom, fdom); - if ( rc ) - goto out; + /* The following check prevents us from doing a XENMEM_add_to_physmap + * between two domU's. Asking for suggestions on how to remove or + * work around it. + * + * rc = xsm_map_gmfn_foreign(XSM_TARGET, tdom, fdom); + * if ( rc ) + * goto out; + */ /* * Take a refcnt on the mfn. NB: following supported for foreign mapping:
Two checks in the p2m code forbids sharing physical pages among DomU's by using xc_add_to_physmap_batch with XENMAPSPACE_gmfn_foreign. Just simply remove them in this RFC patch to ask for suggestions on how to properly handle this. This is for the proposal "Allow setting up shared memory areas between VMs from xl config file" (see [1]). [1] https://lists.xenproject.org/archives/html/xen-devel/2017-07/msg03047.html Signed-off-by: Zhongze Liu <blackskygg@gmail.com> --- Cc: George Dunlap <george.dunlap@eu.citrix.com> Cc: Jan Beulich <jbeulich@suse.com> Cc: Andrew Cooper <andrew.cooper3@citrix.com> Cc: Stefano Stabellini <sstabellini@kernel.org> Cc: Julien Grall <julien.grall@arm.com> Cc: xen-devel@lists.xen.org --- xen/arch/x86/mm/p2m.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-)