[Xen-devel] [PATCH RFC 12/14] xen: vmx: Support for clear EPT SPP write Protect bit

[Zhang Yi <yi.z.zhang@xxxxxxxxxxxxxxx>]

From: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>

This is a implement of clear the Write protect bit.

EPT SPP Write Protect bit will remove when we set all the 32 sub-pages
is writeable. We should also update the EPT page frame w bit as the
whole page is writeable.

Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxx>
---
 xen/arch/x86/mm/mem_access.c | 12 +++++++++---
 xen/arch/x86/mm/p2m-ept.c    | 17 +++++++++++++----
 xen/include/asm-x86/p2m.h    |  2 +-
 3 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
index fdedc4a..fddb6e3 100644
--- a/xen/arch/x86/mm/mem_access.c
+++ b/xen/arch/x86/mm/mem_access.c
@@ -466,7 +466,7 @@ int p2m_get_mem_access(struct domain *d, gfn_t gfn, 
xenmem_access_t *access)
     return _p2m_get_mem_access(p2m, gfn, access);
 }
 
-int p2m_set_mem_spp_wp(struct domain *d, gfn_t gfn)
+int p2m_set_mem_spp_wp(struct domain *d, gfn_t gfn, bool spp, bool w)
 {
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
     mfn_t mfn;
@@ -482,8 +482,9 @@ int p2m_set_mem_spp_wp(struct domain *d, gfn_t gfn)
         rc = -1;
         goto unlock_exit;
     }
+
     if ( p2m->update_ept_spp_wp )
-        rc = p2m->update_ept_spp_wp(p2m, gfn_l);
+        rc = p2m->update_ept_spp_wp(p2m, gfn_l, spp, w);
 
 unlock_exit:
     p2m_unlock(p2m);
@@ -528,7 +529,12 @@ int p2m_set_spp_page_st(struct domain *d, gfn_t gfn, 
uint32_t access_map)
 int p2m_set_subpage(struct domain *d, gfn_t gfn, uint32_t access_map)
 {
     int ret;
-    ret = p2m_set_mem_spp_wp(d, gfn);
+    bool w, spp = 0;
+
+    w = !~access_map;
+    spp = !w;
+    printk("SPP: Set subpage spp=%d, is write:%d\n", spp, w);
+    ret = p2m_set_mem_spp_wp(d, gfn, spp, w);
     if ( ret < 0 )
     {
         printk("SPP: Set subpage ept wp failed!! %x\n", ret);
diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 065beb9..55c3ded 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -46,6 +46,11 @@ static inline bool_t is_epte_valid(ept_entry_t *e)
     return ((e->epte & ~(1ul << 63)) != 0 && e->sa_p2mt != p2m_invalid);
 }
 
+static inline bool_t is_epte_spp_wp(ept_entry_t *e)
+{
+    return ( e->spp && !(e->w) && (e->access == p2m_access_spp) );
+}
+
 /* returns : 0 for success, -errno otherwise */
 static int atomic_write_ept_entry(ept_entry_t *entryptr, ept_entry_t new,
                                   int level)
@@ -725,7 +730,7 @@ bool_t ept_handle_misconfig(uint64_t gpa)
 }
 
 static int
-ept_spp_update_wp(struct p2m_domain *p2m, unsigned long gfn)
+ept_spp_update_wp(struct p2m_domain *p2m, unsigned long gfn, bool spp, bool w)
 {
     ept_entry_t *table, *ept_entry = NULL;
     unsigned long gfn_remainder = gfn;
@@ -754,12 +759,16 @@ ept_spp_update_wp(struct p2m_domain *p2m, unsigned long 
gfn)
         goto out;
     }
 
+    if ( is_epte_spp_wp(ept_entry) && spp )
+        goto sync_out;
+
     new_entry = atomic_read_ept_entry(ept_entry);
-    new_entry.spp = 1;
-    new_entry.w = 0;
-    new_entry.access = p2m_access_spp;
+    new_entry.spp = spp;
+    new_entry.w = w;
+    new_entry.access = spp? p2m_access_spp:p2m_access_n;
     write_atomic(&(ept_entry->epte), new_entry.epte);
 
+sync_out:
     ept_sync_domain(p2m);
     rc = 0;
 out:
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index b94ebb2..36d1cc9 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -267,7 +267,7 @@ struct p2m_domain {
                                           l1_pgentry_t new, unsigned int 
level);
     long               (*audit_p2m)(struct p2m_domain *p2m);
     int                (*update_ept_spp_wp)(struct p2m_domain *p2m,
-                                 unsigned long gfn);
+                                 unsigned long gfn, bool spp, bool w);
     int                (*spp_set_entry)(struct p2m_domain *p2m,
                                 unsigned long gfn,
                                 u64 access);
-- 
2.7.4


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