[PATCH v2 06/18] x86/pv: set/clear guest GDT mappings using {populate,destroy}_perdomain_mapping()

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

The pv_{set,destroy}_gdt() functions rely on the L1 table(s) that contain such
mappings being stashed in the domain structure, and thus such mappings being
modified by merely updating the L1 entries.

Switch both pv_{set,destroy}_gdt() to instead use
{populate,destory}_perdomain_mapping().

Note that this requires moving the pv_set_gdt() call in arch_set_info_guest()
strictly after update_cr3(), so v->arch.cr3 is valid when
populate_perdomain_mapping() is called.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/domain.c               | 33 ++++++++++++++---------------
 xen/arch/x86/pv/descriptor-tables.c | 28 +++++++++++-------------
 2 files changed, 28 insertions(+), 33 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 0bd0ef7e40f4..0481164f3727 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1376,22 +1376,6 @@ int arch_set_info_guest(
     if ( rc )
         return rc;
 
-    if ( !compat )
-        rc = pv_set_gdt(v, c.nat->gdt_frames, c.nat->gdt_ents);
-#ifdef CONFIG_COMPAT
-    else
-    {
-        unsigned long gdt_frames[ARRAY_SIZE(v->arch.pv.gdt_frames)];
-
-        for ( i = 0; i < nr_gdt_frames; ++i )
-            gdt_frames[i] = c.cmp->gdt_frames[i];
-
-        rc = pv_set_gdt(v, gdt_frames, c.cmp->gdt_ents);
-    }
-#endif
-    if ( rc != 0 )
-        return rc;
-
     set_bit(_VPF_in_reset, &v->pause_flags);
 
 #ifdef CONFIG_COMPAT
@@ -1492,7 +1476,6 @@ int arch_set_info_guest(
     {
         if ( cr3_page )
             put_page(cr3_page);
-        pv_destroy_gdt(v);
         return rc;
     }
 
@@ -1508,6 +1491,22 @@ int arch_set_info_guest(
         paging_update_paging_modes(v);
     else
         update_cr3(v);
+
+    if ( !compat )
+        rc = pv_set_gdt(v, c.nat->gdt_frames, c.nat->gdt_ents);
+#ifdef CONFIG_COMPAT
+    else
+    {
+        unsigned long gdt_frames[ARRAY_SIZE(v->arch.pv.gdt_frames)];
+
+        for ( i = 0; i < nr_gdt_frames; ++i )
+            gdt_frames[i] = c.cmp->gdt_frames[i];
+
+        rc = pv_set_gdt(v, gdt_frames, c.cmp->gdt_ents);
+    }
+#endif
+    if ( rc != 0 )
+        return rc;
 #endif /* CONFIG_PV */
 
  out:
diff --git a/xen/arch/x86/pv/descriptor-tables.c 
b/xen/arch/x86/pv/descriptor-tables.c
index 02647a2c5047..5a79f022ce13 100644
--- a/xen/arch/x86/pv/descriptor-tables.c
+++ b/xen/arch/x86/pv/descriptor-tables.c
@@ -49,23 +49,20 @@ bool pv_destroy_ldt(struct vcpu *v)
 
 void pv_destroy_gdt(struct vcpu *v)
 {
-    l1_pgentry_t *pl1e = pv_gdt_ptes(v);
-    mfn_t zero_mfn = _mfn(virt_to_mfn(zero_page));
-    l1_pgentry_t zero_l1e = l1e_from_mfn(zero_mfn, __PAGE_HYPERVISOR_RO);
     unsigned int i;
 
     ASSERT(v == current || !vcpu_cpu_dirty(v));
 
-    v->arch.pv.gdt_ents = 0;
-    for ( i = 0; i < FIRST_RESERVED_GDT_PAGE; i++ )
-    {
-        mfn_t mfn = l1e_get_mfn(pl1e[i]);
+    if ( v->arch.cr3 )
+        destroy_perdomain_mapping(v, GDT_VIRT_START(v),
+                                  ARRAY_SIZE(v->arch.pv.gdt_frames));
 
-        if ( (l1e_get_flags(pl1e[i]) & _PAGE_PRESENT) &&
-             !mfn_eq(mfn, zero_mfn) )
-            put_page_and_type(mfn_to_page(mfn));
+    for ( i = 0; i < ARRAY_SIZE(v->arch.pv.gdt_frames); i++)
+    {
+        if ( !v->arch.pv.gdt_frames[i] )
+            break;
 
-        l1e_write(&pl1e[i], zero_l1e);
+        put_page_and_type(mfn_to_page(_mfn(v->arch.pv.gdt_frames[i])));
         v->arch.pv.gdt_frames[i] = 0;
     }
 }
@@ -74,8 +71,8 @@ int pv_set_gdt(struct vcpu *v, const unsigned long frames[],
                unsigned int entries)
 {
     struct domain *d = v->domain;
-    l1_pgentry_t *pl1e;
     unsigned int i, nr_frames = DIV_ROUND_UP(entries, 512);
+    mfn_t mfns[ARRAY_SIZE(v->arch.pv.gdt_frames)];
 
     ASSERT(v == current || !vcpu_cpu_dirty(v));
 
@@ -90,6 +87,8 @@ int pv_set_gdt(struct vcpu *v, const unsigned long frames[],
         if ( !mfn_valid(mfn) ||
              !get_page_and_type(mfn_to_page(mfn), d, PGT_seg_desc_page) )
             goto fail;
+
+        mfns[i] = mfn;
     }
 
     /* Tear down the old GDT. */
@@ -97,12 +96,9 @@ int pv_set_gdt(struct vcpu *v, const unsigned long frames[],
 
     /* Install the new GDT. */
     v->arch.pv.gdt_ents = entries;
-    pl1e = pv_gdt_ptes(v);
     for ( i = 0; i < nr_frames; i++ )
-    {
         v->arch.pv.gdt_frames[i] = frames[i];
-        l1e_write(&pl1e[i], l1e_from_pfn(frames[i], __PAGE_HYPERVISOR_RW));
-    }
+    populate_perdomain_mapping(v, GDT_VIRT_START(v), mfns, nr_frames);
 
     return 0;
 
-- 
2.46.0