[Xen-devel] [PATCH v2 4/6] xen/arm: implement get/put_page_type

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Add a basic get_page_type and put_page_type implementation: the
implementation is similar to the x86 one, without all the code to handle
shadow pagetables and other unneeded features.

Also remove PGT_shared_page, that is unused.



Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
---
 xen/arch/arm/dummy.S     |    4 --
 xen/arch/arm/mm.c        |   91 ++++++++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-arm/mm.h |    1 -
 3 files changed, 91 insertions(+), 5 deletions(-)

diff --git a/xen/arch/arm/dummy.S b/xen/arch/arm/dummy.S
index baced25..2b96d22 100644
--- a/xen/arch/arm/dummy.S
+++ b/xen/arch/arm/dummy.S
@@ -22,10 +22,6 @@ DUMMY(arch_get_info_guest);
 DUMMY(arch_vcpu_reset);
 NOP(update_vcpu_system_time);
 
-/* Page Reference & Type Maintenance */
-DUMMY(get_page_type);
-DUMMY(put_page_type);
-
 /* Grant Tables */
 DUMMY(steal_page);
 
diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 01a6781..7033023 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -28,8 +28,10 @@
 #include <xen/guest_access.h>
 #include <asm/page.h>
 #include <asm/current.h>
+#include <asm/flushtlb.h>
 #include <public/memory.h>
 #include <xen/sched.h>
+#include <xen/perfc.h>
 
 struct domain *dom_xen, *dom_io;
 
@@ -604,6 +606,95 @@ int get_page(struct page_info *page, struct domain *domain)
     return 0;
 }
 
+void put_page_type(struct page_info *page)
+{
+    unsigned long nx, x, y = page->u.inuse.type_info;
+
+    for ( ; ; )
+    {
+        x  = y;
+        nx = x - 1;
+
+        ASSERT((x & PGT_count_mask) != 0);
+
+        if ( unlikely((nx & PGT_count_mask) == 0) )
+            /*
+             * Record TLB information for flush later
+             */
+            page->tlbflush_timestamp = tlbflush_current_time();
+
+        if ( likely((y = cmpxchg(&page->u.inuse.type_info, x, nx)) == x) )
+            break;
+    }
+}
+
+int get_page_type(struct page_info *page, unsigned long type)
+{
+    unsigned long nx, x, y = page->u.inuse.type_info;
+
+    for ( ; ; )
+    {
+        x  = y;
+        nx = x + 1;
+        if ( unlikely((nx & PGT_count_mask) == 0) )
+        {
+            printk("Type count overflow on pfn %lx", page_to_mfn(page));
+            return -EINVAL;
+        }
+        else if ( (x & PGT_count_mask) == 0 )
+        {
+            struct domain *d = page_get_owner(page);
+
+            if ( (x & PGT_type_mask) != type )
+            {
+                /*
+                 * On type change we check to flush stale TLB entries. This 
+                 * may be unnecessary (e.g., page was GDT/LDT) but those 
+                 * circumstances should be very rare.
+                 */
+                cpumask_t mask;
+
+                cpumask_copy(&mask, d->domain_dirty_cpumask);
+
+                /* Don't flush if the timestamp is old enough */
+                tlbflush_filter(mask, page->tlbflush_timestamp);
+
+                if ( unlikely(!cpumask_empty(&mask)) )
+                {
+                    perfc_incr(need_flush_tlb_flush);
+                    flush_tlb_mask(&mask);
+                }
+
+                /* We lose existing type and validity. */
+                nx &= ~(PGT_type_mask | PGT_validated);
+                nx |= type;
+
+                /* No special validation needed for writable pages. */
+                /* Page tables and GDT/LDT need to be scanned for validity. */
+                if ( type == PGT_writable_page )
+                    nx |= PGT_validated;
+            }
+        }
+        else if ( unlikely(!(x & PGT_validated)) )
+        {
+                /* Someone else is updating validation of this page. Wait... */
+                while ( (y = page->u.inuse.type_info) == x )
+                {
+                    cpu_relax();
+                }
+                continue;
+        }
+
+        if ( likely((y = cmpxchg(&page->u.inuse.type_info, x, nx)) == x) )
+            break;
+    }
+
+    if ( unlikely(!(nx & PGT_validated)) )
+        BUG();
+
+    return 1;
+}
+
 void gnttab_clear_flag(unsigned long nr, uint16_t *addr)
 {
     /*
diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
index 53801b0..b37bd35 100644
--- a/xen/include/asm-arm/mm.h
+++ b/xen/include/asm-arm/mm.h
@@ -71,7 +71,6 @@ struct page_info
 
 #define PGT_none          PG_mask(0, 4)  /* no special uses of this page   */
 #define PGT_writable_page PG_mask(7, 4)  /* has writable mappings?         */
-#define PGT_shared_page   PG_mask(8, 4)  /* CoW sharable page              */
 #define PGT_type_mask     PG_mask(15, 4) /* Bits 28-31 or 60-63.           */
 
  /* Owning guest has pinned this page to its current type? */
-- 
1.7.2.5


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