Re: [PATCH] altp2m: Allow the hostp2m to be shared

[Tamas K Lengyel <tamas@tklengyel.com>]

[-- Attachment #1.1: Type: text/plain, Size: 4491 bytes --]

On Wed, Apr 27, 2016 at 9:31 AM, George Dunlap <george.dunlap@citrix.com>
wrote:

> On 27/04/16 16:18, Tamas K Lengyel wrote:
> > On Wed, Apr 27, 2016 at 9:01 AM, George Dunlap <george.dunlap@citrix.com
> >
> > wrote:
> >
> >> On 21/04/16 18:10, Tamas K Lengyel wrote:
> >>> Don't propagate altp2m changes from ept_set_entry for memshare as
> >> memshare
> >>> already has the lock. We call altp2m propagate changes once memshare
> >>> successfully finishes. Also, allow the hostp2m entries to be of type
> >>> p2m_ram_shared.
> >>>
> >>> Signed-off-by: Tamas K Lengyel <tamas@tklengyel.com>
> >>
> >> Sorry for the delay in reviewing -- trying to get my head back around
> >> the altp2m code.  On the whole looks reasonable, but one question...
> >>
> >>> ---
> >>> Cc: George Dunlap <george.dunlap@eu.citrix.com>
> >>> Cc: Keir Fraser <keir@xen.org>
> >>> Cc: Jan Beulich <jbeulich@suse.com>
> >>> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> >>> Cc: Jun Nakajima <jun.nakajima@intel.com>
> >>> Cc: Kevin Tian <kevin.tian@intel.com>
> >>> ---
> >>>  xen/arch/x86/mm/mem_sharing.c | 11 +++++++++++
> >>>  xen/arch/x86/mm/p2m-ept.c     |  2 +-
> >>>  xen/arch/x86/mm/p2m.c         |  7 +++----
> >>>  3 files changed, 15 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/xen/arch/x86/mm/mem_sharing.c
> >> b/xen/arch/x86/mm/mem_sharing.c
> >>> index a522423..d5b4b2d 100644
> >>> --- a/xen/arch/x86/mm/mem_sharing.c
> >>> +++ b/xen/arch/x86/mm/mem_sharing.c
> >>> @@ -35,6 +35,7 @@
> >>>  #include <asm/p2m.h>
> >>>  #include <asm/atomic.h>
> >>>  #include <asm/event.h>
> >>> +#include <asm/altp2m.h>
> >>>  #include <xsm/xsm.h>
> >>>
> >>>  #include "mm-locks.h"
> >>> @@ -1026,6 +1027,16 @@ int mem_sharing_share_pages(struct domain *sd,
> >> unsigned long sgfn, shr_handle_t
> >>>      /* We managed to free a domain page. */
> >>>      atomic_dec(&nr_shared_mfns);
> >>>      atomic_inc(&nr_saved_mfns);
> >>> +
> >>> +    if( altp2m_active(cd) )
> >>> +    {
> >>> +        p2m_access_t a;
> >>> +        struct p2m_domain *p2m = p2m_get_hostp2m(cd);
> >>> +        p2m->get_entry(p2m, cgfn, NULL, &a, 0, NULL, NULL);
> >>> +        p2m_altp2m_propagate_change(cd, _gfn(cgfn), smfn,
> PAGE_ORDER_4K,
> >>> +                                    p2m_ram_shared, a);
> >>> +    }
> >>> +
> >>>      ret = 0;
> >>>
> >>>  err_out:
> >>> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> >>> index 3cb6868..1ac3018 100644
> >>> --- a/xen/arch/x86/mm/p2m-ept.c
> >>> +++ b/xen/arch/x86/mm/p2m-ept.c
> >>> @@ -846,7 +846,7 @@ out:
> >>>      if ( is_epte_present(&old_entry) )
> >>>          ept_free_entry(p2m, &old_entry, target);
> >>>
> >>> -    if ( rc == 0 && p2m_is_hostp2m(p2m) )
> >>> +    if ( rc == 0 && p2m_is_hostp2m(p2m) && p2mt != p2m_ram_shared )
> >>>          p2m_altp2m_propagate_change(d, _gfn(gfn), mfn, order, p2mt,
> >> p2ma);
> >>>
> >>>      return rc;
> >>> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> >>> index b3fce1b..d2aebf7 100644
> >>> --- a/xen/arch/x86/mm/p2m.c
> >>> +++ b/xen/arch/x86/mm/p2m.c
> >>> @@ -1739,11 +1739,10 @@ int p2m_set_altp2m_mem_access(struct domain *d,
> >> struct p2m_domain *hp2m,
> >>>      /* Check host p2m if no valid entry in alternate */
> >>>      if ( !mfn_valid(mfn) )
> >>>      {
> >>> -        mfn = hp2m->get_entry(hp2m, gfn_l, &t, &old_a,
> >>> -                              P2M_ALLOC | P2M_UNSHARE, &page_order,
> >> NULL);
> >>> +        mfn = hp2m->get_entry(hp2m, gfn_l, &t, &old_a, 0, &page_order,
> >> NULL);
> >>
> >> Why are you getting rid of P2M_ALLOC here?  What happens if the hp2m
> >> entry is populate-on-demand?
> >>
> >
> > There is a check further down here that only allows p2m_ram_rw and
> > p2m_ram_shared.
>
> So what P2M_ALLOC means is, "If this is entry is PoD, then please
> populate it so I get a ram page."  So the only way you can get a
> p2m_populate_on_demand type returned is if you remove this flag.  Leave
> it and (assuming there's enough ram to go around), you'll always get
> p2m_ram_rw.  :-)
>
> > On the non-altp2m path mem_access doesn't request P2M_ALLOC
> > either (but doesn't check the type), so I would say mem_access is not
> > compatible with PoD.
>
> Off the top of my head I can't see a reason why they couldn't co-exist
> in principle, if you added P2M_ALLOC in a few key places.
>

Sure, I just rather do that in a separate patch and for now have the
mem_access paths behaving the same way before doing that adjustment.

Tamas

[-- Attachment #1.2: Type: text/html, Size: 6744 bytes --]

[-- Attachment #2: Type: text/plain, Size: 126 bytes --]

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel