[Xen-devel] [PATCH RFC 07/14] xen: vmx: Update the EPT leaf entry indicated with the SPP enable bit.

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

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

If the sub-page write permission VM-execution control is set,
treatment of write accesses to guest-physical accesses
depends on the state of the accumulated write-access bit (position 1)
and sub-page permission bit (position 61) in the EPT leaf
paging-structure.

Software will update the EPT leaf entry sub-page permission bit while
kvm_set_subpage. If the EPT write-access bit set to 0 and the SPP bit
set to 1 in the leaf EPT paging-structure entry that maps a 4KB page,
then the hardware will look up a VMM-managed Sub-Page Permission Table
(SPPT), which will also be prepared by setup kvm_set_subpage.

Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/mm/mem_access.c | 24 ++++++++++++++++++++++
 xen/arch/x86/mm/p2m-ept.c    | 47 ++++++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-x86/p2m.h    |  2 ++
 3 files changed, 73 insertions(+)

diff --git a/xen/arch/x86/mm/mem_access.c b/xen/arch/x86/mm/mem_access.c
index 5adaf6d..a471c74 100644
--- a/xen/arch/x86/mm/mem_access.c
+++ b/xen/arch/x86/mm/mem_access.c
@@ -466,6 +466,30 @@ 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)
+{
+    struct p2m_domain *p2m = p2m_get_hostp2m(d);
+    mfn_t mfn;
+    p2m_access_t old_a;
+    int rc = -1;
+    p2m_type_t t;
+    unsigned long gfn_l = gfn_x(gfn);
+
+    p2m_lock(p2m);
+    mfn = p2m->get_entry(p2m, gfn_l, &t, &old_a, 0, NULL, NULL);
+    if( mfn_eq(mfn, INVALID_MFN) )
+    {
+        rc = -1;
+        goto unlock_exit;
+    }
+    if ( p2m->update_ept_spp_wp )
+        rc = p2m->update_ept_spp_wp(p2m, gfn_l);
+
+unlock_exit:
+    p2m_unlock(p2m);
+    return rc;
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 8d9da92..c249286 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -667,6 +667,48 @@ bool_t ept_handle_misconfig(uint64_t gpa)
     return spurious ? (rc >= 0) : (rc > 0);
 }
 
+static int
+ept_spp_update_wp(struct p2m_domain *p2m, unsigned long gfn)
+{
+    ept_entry_t *table, *ept_entry = NULL;
+    unsigned long gfn_remainder = gfn;
+    ept_entry_t new_entry = { .epte = 0 };
+    struct ept_data *ept = &p2m->ept;
+    unsigned int i;
+    int ret, rc;
+
+    table = map_domain_page(_mfn(pagetable_get_pfn(p2m_get_pagetable(p2m))));
+
+    ret = GUEST_TABLE_MAP_FAILED;
+    for ( i = ept->wl; i > 0; i-- )
+    {
+        ret = ept_next_level(p2m, 0, &table, &gfn_remainder, i);
+        if ( ret != GUEST_TABLE_NORMAL_PAGE )
+        {
+            rc = -ENOENT;
+            goto out;
+        }
+    }
+
+    ept_entry = table + (gfn_remainder >> (i * EPT_TABLE_ORDER));
+    if ( !is_epte_present(ept_entry) )
+    {
+        rc = -ENOENT;
+        goto out;
+    }
+
+    new_entry = atomic_read_ept_entry(ept_entry);
+    new_entry.spp = 1;
+    new_entry.w = 0;
+    write_atomic(&(ept_entry->epte), new_entry.epte);
+
+    ept_sync_domain(p2m);
+    rc = 0;
+out:
+    unmap_domain_page(table);
+    return rc;
+}
+
 /*
  * ept_set_entry() computes 'need_modify_vtd_table' for itself,
  * by observing whether any gfn->mfn translations are modified.
@@ -1264,6 +1306,11 @@ int ept_p2m_init(struct p2m_domain *p2m)
         p2m->flush_hardware_cached_dirty = ept_flush_pml_buffers;
     }
 
+    if ( cpu_has_vmx_ept_spp )
+    {
+        p2m->update_ept_spp_wp = ept_spp_update_wp;
+    }
+
     if ( !zalloc_cpumask_var(&ept->invalidate) )
         return -ENOMEM;
 
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 0561643..adbc1c6 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -266,6 +266,8 @@ struct p2m_domain {
                                           unsigned long gfn, l1_pgentry_t *p,
                                           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);
 
     /*
      * P2M updates may require TLBs to be flushed (invalidated).
-- 
2.7.4


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