Keep two virtual pages as mapping windows to access physical memory

PCI devices expose their memory etc. way beyond last_phys_addr. Userland
drivers opening /dev/mem need to open those too, even if phystokv() will
not work for them.

* i386/intel/pmap.h (pmap_mapwindow_t): New type.
(pmap_get_mapwindow, pmap_put_mapwindow): New prototypes.
(PMAP_NMAPWINDOWS): New macro.
* i386/intel/pmap.c (mapwindows): New array.
(pmap_get_mapwindow, pmap_put_mapwindow): New functions.
(pmap_bootstrap, pmap_virtual_space): Reserve virtual pages for the mapping
windows.
* i386/i386/phys.c: Include <i386/model_dep.h>
(INTEL_PTE_W, INTEL_PTE_R): New macros
(pmap_zero_page, pmap_copy_page, copy_to_phys, copy_from_phys): Use
`pmap_get_mapwindow' to temporarily map physical pages beyond last_phys_addr.

2 files changed, 52 insertions, 1 deletions

diff --git a/i386/intel/pmap.c b/i386/intel/pmap.c
index 2943d26..a3d9630 100644
--- a/i386/intel/pmap.c
+++ b/i386/intel/pmap.c
@@ -419,6 +419,12 @@ unsigned int	inuse_ptepages_count = 0;	/* debugging */
  */
 pt_entry_t *kernel_page_dir;
 
+/*
+ * Two slots for temporary physical page mapping, to allow for
+ * physical-to-physical transfers.
+ */
+static pmap_mapwindow_t mapwindows[PMAP_NMAPWINDOWS];
+
 static inline pt_entry_t *
 pmap_pde(const pmap_t pmap, vm_offset_t addr)
 {
@@ -774,6 +780,12 @@ void pmap_bootstrap(void)
 			}
 			for (; pte < ptable+NPTES; pte++)
 			{
+				if (va >= kernel_virtual_end - PMAP_NMAPWINDOWS * PAGE_SIZE);
+				{
+					pmap_mapwindow_t *win = &mapwindows[atop(va - (kernel_virtual_end - PMAP_NMAPWINDOWS * PAGE_SIZE))];
+					win->entry = pte;
+					win->vaddr = va;
+				}
 				WRITE_PTE(pte, 0);
 				va += INTEL_PGBYTES;
 			}
@@ -884,12 +896,41 @@ void pmap_clear_bootstrap_pagetable(pt_entry_t *base) {
 }
 #endif	/* MACH_PV_PAGETABLES */
 
+/*
+ * Create a temporary mapping for a given physical entry
+ *
+ * This can be used to access physical pages which are not mapped 1:1 by
+ * phystokv().
+ */
+pmap_mapwindow_t *pmap_get_mapwindow(pt_entry_t entry)
+{
+	pmap_mapwindow_t *map;
+
+	/* Find an empty one.  */
+	for (map = &mapwindows[0]; map < &mapwindows[sizeof (mapwindows) / sizeof (*mapwindows)]; map++)
+		if (!(*map->entry))
+			break;
+	assert(map < &mapwindows[sizeof (mapwindows) / sizeof (*mapwindows)]);
+
+	WRITE_PTE(map->entry, entry);
+	return map;
+}
+
+/*
+ * Destroy a temporary mapping for a physical entry
+ */
+void pmap_put_mapwindow(pmap_mapwindow_t *map)
+{
+	WRITE_PTE(map->entry, 0);
+	PMAP_UPDATE_TLBS(kernel_pmap, map->vaddr, map->vaddr + PAGE_SIZE);
+}
+
 void pmap_virtual_space(startp, endp)
 	vm_offset_t *startp;
 	vm_offset_t *endp;
 {
 	*startp = kernel_virtual_start;
-	*endp = kernel_virtual_end;
+	*endp = kernel_virtual_end - PMAP_NMAPWINDOWS * PAGE_SIZE;
 }
 
 /*
diff --git a/i386/intel/pmap.h b/i386/intel/pmap.h
index 047a384..382cd5f 100644
--- a/i386/intel/pmap.h
+++ b/i386/intel/pmap.h
@@ -192,6 +192,16 @@ extern void pmap_clear_bootstrap_pagetable(pt_entry_t *addr);
 #define	set_pmap(pmap)	set_cr3(kvtophys((vm_offset_t)(pmap)->dirbase))
 #endif	/* PAE */
 
+typedef struct {
+	pt_entry_t	*entry;
+	vm_offset_t	vaddr;
+} pmap_mapwindow_t;
+
+extern pmap_mapwindow_t *pmap_get_mapwindow(pt_entry_t entry);
+extern void pmap_put_mapwindow(pmap_mapwindow_t *map);
+
+#define PMAP_NMAPWINDOWS 2
+
 #if	NCPUS > 1
 /*
  *	List of cpus that are actively using mapped memory.  Any