[Xen-devel] [PATCH v2] altp2m: Allow the hostp2m to be shared

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

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. Allow the hostp2m entries to be of type
p2m_ram_shared when applying mem_access. Also, do not trigger PoD for hostp2m
when setting altp2m mem_access to be in-line with non-altp2m mem_access path.

Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
---
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
Cc: Kevin Tian <kevin.tian@xxxxxxxxx>

v2: Cosmetic fixes and addressing PoD in the commit message
---
 xen/arch/x86/mm/mem_sharing.c | 10 +++++++++-
 xen/arch/x86/mm/p2m-ept.c     |  2 +-
 xen/arch/x86/mm/p2m.c         |  5 ++---
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index a522423..6693661 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"
@@ -926,11 +927,12 @@ int mem_sharing_share_pages(struct domain *sd, unsigned 
long sgfn, shr_handle_t
     int ret = -EINVAL;
     mfn_t smfn, cmfn;
     p2m_type_t smfn_type, cmfn_type;
+    p2m_access_t cmfn_a;
     struct two_gfns tg;
     struct rmap_iterator ri;
 
     get_two_gfns(sd, sgfn, &smfn_type, NULL, &smfn,
-                 cd, cgfn, &cmfn_type, NULL, &cmfn,
+                 cd, cgfn, &cmfn_type, &cmfn_a, &cmfn,
                  0, &tg);
 
     /* This tricky business is to avoid two callers deadlocking if 
@@ -1026,6 +1028,12 @@ 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);
+
+    /* Save the change to the altp2m tables as well if active */
+    if ( altp2m_active(cd) )
+        p2m_altp2m_propagate_change(cd, _gfn(cgfn), smfn, PAGE_ORDER_4K,
+                                    p2m_ram_shared, cmfn_a);
+
     ret = 0;
     
 err_out:
diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 1ed5b47..ff84242 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -847,7 +847,7 @@ 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 6eef2f3..2a42b91 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1765,11 +1765,10 @@ 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);
 
         rc = -ESRCH;
-        if ( !mfn_valid(mfn) || t != p2m_ram_rw )
+        if ( !mfn_valid(mfn) || (t != p2m_ram_rw && t != p2m_ram_shared) )
             return rc;
 
         /* If this is a superpage, copy that first */
-- 
2.1.4


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