[Xen-devel] [PATCH] x86/pv: Clean up cr3 handling in arch_set_info_guest()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

All of this code lives inside CONFIG_PV which means gfn == mfn, and the
fill_ro_mpt() calls clearly show that the value is used untranslated.

Change cr3_gfn to a suitably typed cr3_mfn, and replace get_page_from_gfn()
with a straight mfn_to_page/get_page sequence, to avoid the implication that
translation is going on.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>

Julien: This should simplify your "xen: Switch parameter in get_page_from_gfn
to use typesafe gfn" patch.  In particular, I did a doubletake at
fill_ro_mpt(_mfn(gfn_x(cr3_gfn))); when reviewing it.
---
 xen/arch/x86/domain.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 32dc4253..da94ab4 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -827,8 +827,8 @@ int arch_set_info_guest(
     unsigned long flags;
     bool compat;
 #ifdef CONFIG_PV
-    unsigned long cr3_gfn;
-    struct page_info *cr3_page;
+    mfn_t cr3_mfn;
+    struct page_info *cr3_page = NULL;
     unsigned long cr4;
     int rc = 0;
 #endif
@@ -1091,12 +1091,12 @@ int arch_set_info_guest(
     set_bit(_VPF_in_reset, &v->pause_flags);
 
     if ( !compat )
-        cr3_gfn = xen_cr3_to_pfn(c.nat->ctrlreg[3]);
+        cr3_mfn = _mfn(xen_cr3_to_pfn(c.nat->ctrlreg[3]));
     else
-        cr3_gfn = compat_cr3_to_pfn(c.cmp->ctrlreg[3]);
-    cr3_page = get_page_from_gfn(d, cr3_gfn, NULL, P2M_ALLOC);
+        cr3_mfn = _mfn(compat_cr3_to_pfn(c.cmp->ctrlreg[3]));
 
-    if ( !cr3_page )
+    if ( !mfn_valid(cr3_mfn) ||
+         !(cr3_page = mfn_to_page(cr3_mfn), get_page(cr3_page, d)) )
         rc = -EINVAL;
     else if ( paging_mode_refcounts(d) )
         /* nothing */;
@@ -1122,7 +1122,7 @@ int arch_set_info_guest(
         case 0:
             if ( !compat && !VM_ASSIST(d, m2p_strict) &&
                  !paging_mode_refcounts(d) )
-                fill_ro_mpt(_mfn(cr3_gfn));
+                fill_ro_mpt(cr3_mfn);
             break;
         default:
             if ( cr3_page == current->arch.old_guest_table )
@@ -1137,10 +1137,10 @@ int arch_set_info_guest(
         v->arch.guest_table = pagetable_from_page(cr3_page);
         if ( c.nat->ctrlreg[1] )
         {
-            cr3_gfn = xen_cr3_to_pfn(c.nat->ctrlreg[1]);
-            cr3_page = get_page_from_gfn(d, cr3_gfn, NULL, P2M_ALLOC);
+            cr3_mfn = _mfn(xen_cr3_to_pfn(c.nat->ctrlreg[1]));
 
-            if ( !cr3_page )
+            if ( !mfn_valid(cr3_mfn) ||
+                 !(cr3_page = mfn_to_page(cr3_mfn), get_page(cr3_page, d)) )
                 rc = -EINVAL;
             else if ( !paging_mode_refcounts(d) )
             {
@@ -1162,7 +1162,7 @@ int arch_set_info_guest(
                     break;
                 case 0:
                     if ( VM_ASSIST(d, m2p_strict) )
-                        zap_ro_mpt(_mfn(cr3_gfn));
+                        zap_ro_mpt(cr3_mfn);
                     break;
                 }
             }
-- 
2.1.4


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