diff mbox

[v2,1/3] x86: nuke PV superpage option and code

Message ID 20170726074456.25511-2-wei.liu2@citrix.com (mailing list archive)
State New, archived
Headers show

Commit Message

Wei Liu July 26, 2017, 7:44 a.m. UTC
Delete the user visible option and code for PV superpage support. The
mm code is modified as if the option is set to false (the default
value).

Return the address space occupied by spage_info back to the reserved
address space.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
---
Done some basic testing with xtf, also tested with basic PV guest life
cycle.

v2: Merge the patch to update docs here, rebase on top of staging
---
 docs/misc/xen-command-line.markdown |   7 -
 xen/arch/x86/domain.c               |   2 -
 xen/arch/x86/mm.c                   | 257 ++----------------------------------
 xen/arch/x86/pv/dom0_build.c        |   2 -
 xen/include/asm-x86/config.h        |  16 +--
 xen/include/asm-x86/mm.h            |  20 ---
 xen/include/asm-x86/page.h          |  11 --
 xen/include/asm-x86/paging.h        |   3 +-
 xen/include/asm-x86/x86_64/page.h   |   2 -
 9 files changed, 13 insertions(+), 307 deletions(-)

Comments

Andrew Cooper July 26, 2017, 4:19 p.m. UTC | #1
On 26/07/17 08:44, Wei Liu wrote:
> Delete the user visible option and code for PV superpage support. The
> mm code is modified as if the option is set to false (the default
> value).
>
> Return the address space occupied by spage_info back to the reserved
> address space.
>
> Signed-off-by: Wei Liu <wei.liu2@citrix.com>

XenServer sanity checking doesn't have any objections.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

I'd prefer an Ack from Konrad/Boris though, seeing as this was an Oracle
feature originally (even though we were given permission to rip it out).

~Andrew
Wei Liu July 26, 2017, 4:37 p.m. UTC | #2
On Wed, Jul 26, 2017 at 05:19:02PM +0100, Andrew Cooper wrote:
> On 26/07/17 08:44, Wei Liu wrote:
> > Delete the user visible option and code for PV superpage support. The
> > mm code is modified as if the option is set to false (the default
> > value).
> >
> > Return the address space occupied by spage_info back to the reserved
> > address space.
> >
> > Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> 
> XenServer sanity checking doesn't have any objections.
> 
> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> I'd prefer an Ack from Konrad/Boris though, seeing as this was an Oracle
> feature originally (even though we were given permission to rip it out).
> 

There is already one: <20170721170612.GB25182@char.us.oracle.com>

> ~Andrew
Konrad Rzeszutek Wilk July 26, 2017, 7:33 p.m. UTC | #3
On Wed, Jul 26, 2017 at 05:19:02PM +0100, Andrew Cooper wrote:
> On 26/07/17 08:44, Wei Liu wrote:
> > Delete the user visible option and code for PV superpage support. The
> > mm code is modified as if the option is set to false (the default
> > value).
> >
> > Return the address space occupied by spage_info back to the reserved
> > address space.
> >
> > Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> 
> XenServer sanity checking doesn't have any objections.
> 
> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> I'd prefer an Ack from Konrad/Boris though, seeing as this was an Oracle
> feature originally (even though we were given permission to rip it out).

Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

for all this code.

RIP PV superpage.

> 
> ~Andrew
diff mbox

Patch

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index a130452462..4002eab08b 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -133,13 +133,6 @@  resume.
 `s3_mode` instructs Xen to set up the boot time (option `vga=`) video
 mode during S3 resume.
 
-### allowsuperpage
-> `= <boolean>`
-
-> Default: `true`
-
-Permit Xen to use superpages when performing memory management.
-
 ### altp2m (Intel)
 > `= <boolean>`
 
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index dd8bf1302f..1ce804b05f 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1782,8 +1782,6 @@  static int relinquish_memory(
             BUG();
         }
 
-        clear_superpage_mark(page);
-
         if ( test_and_clear_bit(_PGC_allocated, &page->count_info) )
             put_page(page);
 
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 51c93c168f..97b3b4ba2c 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -150,18 +150,11 @@  struct rangeset *__read_mostly mmio_ro_ranges;
 
 #define PAGE_CACHE_ATTRS (_PAGE_PAT|_PAGE_PCD|_PAGE_PWT)
 
-bool __read_mostly opt_allow_superpage;
-boolean_param("allowsuperpage", opt_allow_superpage);
-
-static void put_superpage(unsigned long mfn);
-
 static uint32_t base_disallow_mask;
 /* Global bit is allowed to be set on L1 PTEs. Intended for user mappings. */
 #define L1_DISALLOW_MASK ((base_disallow_mask | _PAGE_GNTTAB) & ~_PAGE_GLOBAL)
 
-#define L2_DISALLOW_MASK (unlikely(opt_allow_superpage) \
-                          ? base_disallow_mask & ~_PAGE_PSE \
-                          : base_disallow_mask)
+#define L2_DISALLOW_MASK base_disallow_mask
 
 #define l3_disallow_mask(d) (!is_pv_32bit_domain(d) ? \
                              base_disallow_mask : 0xFFFFF198U)
@@ -219,15 +212,6 @@  static void __init init_frametable_chunk(void *start, void *end)
     memset(end, -1, s - e);
 }
 
-static void __init init_spagetable(void)
-{
-    BUILD_BUG_ON(XEN_VIRT_END > SPAGETABLE_VIRT_START);
-
-    init_frametable_chunk(spage_table,
-                          mem_hotplug ? spage_table + SPAGETABLE_NR
-                                      : pdx_to_spage(max_pdx - 1) + 1);
-}
-
 void __init init_frametable(void)
 {
     unsigned int sidx, eidx, nidx;
@@ -252,9 +236,6 @@  void __init init_frametable(void)
                          : end_pg;
     init_frametable_chunk(pdx_to_page(sidx * PDX_GROUP_COUNT), top_pg);
     memset(end_pg, -1, (unsigned long)top_pg - (unsigned long)end_pg);
-
-    if (opt_allow_superpage)
-        init_spagetable();
 }
 
 #ifndef NDEBUG
@@ -1129,20 +1110,7 @@  get_page_from_l2e(
         return rc;
     }
 
-    if ( !opt_allow_superpage )
-    {
-        gdprintk(XENLOG_WARNING, "PV superpages disabled in hypervisor\n");
-        return -EINVAL;
-    }
-
-    if ( mfn & (L1_PAGETABLE_ENTRIES - 1) )
-    {
-        gdprintk(XENLOG_WARNING,
-                 "Unaligned superpage map attempt mfn %" PRI_mfn "\n", mfn);
-        return -EINVAL;
-    }
-
-    return get_superpage(mfn, d);
+    return -EINVAL;
 }
 
 
@@ -1315,8 +1283,13 @@  static int put_page_from_l2e(l2_pgentry_t l2e, unsigned long pfn)
         return 1;
 
     if ( l2e_get_flags(l2e) & _PAGE_PSE )
-        put_superpage(l2e_get_pfn(l2e));
-    else
+    {
+        struct page_info *page = mfn_to_page(l2e_get_pfn(l2e));
+        unsigned int i;
+
+        for ( i = 0; i < (1u << PAGETABLE_ORDER); i++, page++ )
+            put_page_and_type(page);
+    } else
         put_page_and_type(l2e_get_page(l2e));
 
     return 0;
@@ -2676,197 +2649,6 @@  int get_page_type_preemptible(struct page_info *page, unsigned long type)
     return __get_page_type(page, type, 1);
 }
 
-static int get_spage_pages(struct page_info *page, struct domain *d)
-{
-    unsigned int i;
-
-    for ( i = 0; i < (1u << PAGETABLE_ORDER); i++, page++ )
-    {
-        if ( !get_page_and_type(page, d, PGT_writable_page) )
-        {
-            while ( i-- > 0 )
-                put_page_and_type(--page);
-            return 0;
-        }
-    }
-    return 1;
-}
-
-static void put_spage_pages(struct page_info *page)
-{
-    unsigned int i;
-
-    for ( i = 0; i < (1u << PAGETABLE_ORDER); i++, page++ )
-        put_page_and_type(page);
-}
-
-static int mark_superpage(struct spage_info *spage, struct domain *d)
-{
-    unsigned long x, nx, y = spage->type_info;
-    int pages_done = 0;
-
-    ASSERT(opt_allow_superpage);
-
-    do {
-        x = y;
-        nx = x + 1;
-        if ( (x & SGT_type_mask) == SGT_mark )
-        {
-            gdprintk(XENLOG_WARNING,
-                     "Duplicate superpage mark attempt mfn %" PRI_mfn "\n",
-                     spage_to_mfn(spage));
-            if ( pages_done )
-                put_spage_pages(spage_to_page(spage));
-            return -EINVAL;
-        }
-        if ( (x & SGT_type_mask) == SGT_dynamic )
-        {
-            if ( pages_done )
-            {
-                put_spage_pages(spage_to_page(spage));
-                pages_done = 0;
-            }
-        }
-        else if ( !pages_done )
-        {
-            if ( !get_spage_pages(spage_to_page(spage), d) )
-            {
-                gdprintk(XENLOG_WARNING,
-                         "Superpage type conflict in mark attempt mfn %" PRI_mfn "\n",
-                         spage_to_mfn(spage));
-                return -EINVAL;
-            }
-            pages_done = 1;
-        }
-        nx = (nx & ~SGT_type_mask) | SGT_mark;
-
-    } while ( (y = cmpxchg(&spage->type_info, x, nx)) != x );
-
-    return 0;
-}
-
-static int unmark_superpage(struct spage_info *spage)
-{
-    unsigned long x, nx, y = spage->type_info;
-    unsigned long do_pages = 0;
-
-    ASSERT(opt_allow_superpage);
-
-    do {
-        x = y;
-        nx = x - 1;
-        if ( (x & SGT_type_mask) != SGT_mark )
-        {
-            gdprintk(XENLOG_WARNING,
-                     "Attempt to unmark unmarked superpage mfn %" PRI_mfn "\n",
-                     spage_to_mfn(spage));
-            return -EINVAL;
-        }
-        if ( (nx & SGT_count_mask) == 0 )
-        {
-            nx = (nx & ~SGT_type_mask) | SGT_none;
-            do_pages = 1;
-        }
-        else
-        {
-            nx = (nx & ~SGT_type_mask) | SGT_dynamic;
-        }
-    } while ( (y = cmpxchg(&spage->type_info, x, nx)) != x );
-
-    if ( do_pages )
-        put_spage_pages(spage_to_page(spage));
-
-    return 0;
-}
-
-void clear_superpage_mark(struct page_info *page)
-{
-    struct spage_info *spage;
-
-    if ( !opt_allow_superpage )
-        return;
-
-    spage = page_to_spage(page);
-    if ((spage->type_info & SGT_type_mask) == SGT_mark)
-        unmark_superpage(spage);
-
-}
-
-int get_superpage(unsigned long mfn, struct domain *d)
-{
-    struct spage_info *spage;
-    unsigned long x, nx, y;
-    int pages_done = 0;
-
-    ASSERT(opt_allow_superpage);
-
-    if ( !mfn_valid(_mfn(mfn | (L1_PAGETABLE_ENTRIES - 1))) )
-        return -EINVAL;
-
-    spage = mfn_to_spage(mfn);
-    y = spage->type_info;
-    do {
-        x = y;
-        nx = x + 1;
-        if ( (x & SGT_type_mask) != SGT_none )
-        {
-            if ( pages_done )
-            {
-                put_spage_pages(spage_to_page(spage));
-                pages_done = 0;
-            }
-        }
-        else
-        {
-            if ( !get_spage_pages(spage_to_page(spage), d) )
-            {
-                gdprintk(XENLOG_WARNING,
-                         "Type conflict on superpage mapping mfn %" PRI_mfn "\n",
-                         spage_to_mfn(spage));
-                return -EINVAL;
-            }
-            pages_done = 1;
-            nx = (nx & ~SGT_type_mask) | SGT_dynamic;
-        }
-    } while ( (y = cmpxchg(&spage->type_info, x, nx)) != x );
-
-    return 0;
-}
-
-static void put_superpage(unsigned long mfn)
-{
-    struct spage_info *spage;
-    unsigned long x, nx, y;
-    unsigned long do_pages = 0;
-
-    if ( !opt_allow_superpage )
-    {
-        put_spage_pages(mfn_to_page(mfn));
-        return;
-    }
-
-    spage = mfn_to_spage(mfn);
-    y = spage->type_info;
-    do {
-        x = y;
-        nx = x - 1;
-        if ((x & SGT_type_mask) == SGT_dynamic)
-        {
-            if ((nx & SGT_count_mask) == 0)
-            {
-                nx = (nx & ~SGT_type_mask) | SGT_none;
-                do_pages = 1;
-            }
-        }
-
-    } while ((y = cmpxchg(&spage->type_info, x, nx)) != x);
-
-    if (do_pages)
-        put_spage_pages(spage_to_page(spage));
-
-    return;
-}
-
 int put_old_guest_table(struct vcpu *v)
 {
     int rc;
@@ -3599,27 +3381,8 @@  long do_mmuext_op(
 
         case MMUEXT_MARK_SUPER:
         case MMUEXT_UNMARK_SUPER:
-        {
-            unsigned long mfn = op.arg1.mfn;
-
-            if ( !opt_allow_superpage )
-                rc = -EOPNOTSUPP;
-            else if ( unlikely(currd != pg_owner) )
-                rc = -EPERM;
-            else if ( mfn & (L1_PAGETABLE_ENTRIES - 1) )
-            {
-                gdprintk(XENLOG_WARNING,
-                         "Unaligned superpage mfn %" PRI_mfn "\n", mfn);
-                rc = -EINVAL;
-            }
-            else if ( !mfn_valid(_mfn(mfn | (L1_PAGETABLE_ENTRIES - 1))) )
-                rc = -EINVAL;
-            else if ( op.cmd == MMUEXT_MARK_SUPER )
-                rc = mark_superpage(mfn_to_spage(mfn), currd);
-            else
-                rc = unmark_superpage(mfn_to_spage(mfn));
+            rc = -EOPNOTSUPP;
             break;
-        }
 
         default:
             rc = -ENOSYS;
diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
index 18c19a256f..e67ffdd7b8 100644
--- a/xen/arch/x86/pv/dom0_build.c
+++ b/xen/arch/x86/pv/dom0_build.c
@@ -181,8 +181,6 @@  static __init void setup_pv_physmap(struct domain *d, unsigned long pgtbl_pfn,
                                              0)) != NULL )
             {
                 *pl2e = l2e_from_page(page, L1_PROT|_PAGE_DIRTY|_PAGE_PSE);
-                if ( opt_allow_superpage )
-                    get_superpage(page_to_mfn(page), d);
                 vphysmap_start += 1UL << L2_PAGETABLE_SHIFT;
                 continue;
             }
diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
index dc424f99e4..bc0730fd9d 100644
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -143,19 +143,15 @@  extern unsigned char boot_edid_info[128];
  *  0xffff82d080000000 - 0xffff82d0bfffffff [1GB,   2^30 bytes, PML4:261]
  *    Xen text, static data, bss.
 #ifndef CONFIG_BIGMEM
- *  0xffff82d0c0000000 - 0xffff82dffbffffff [61GB - 64MB,       PML4:261]
+ *  0xffff82d0c0000000 - 0xffff82dfffffffff [61GB,              PML4:261]
  *    Reserved for future use.
- *  0xffff82dffc000000 - 0xffff82dfffffffff [64MB,  2^26 bytes, PML4:261]
- *    Super-page information array.
  *  0xffff82e000000000 - 0xffff82ffffffffff [128GB, 2^37 bytes, PML4:261]
  *    Page-frame information array.
  *  0xffff830000000000 - 0xffff87ffffffffff [5TB, 5*2^40 bytes, PML4:262-271]
  *    1:1 direct mapping of all physical memory.
 #else
- *  0xffff82d0c0000000 - 0xffff82ffdfffffff [188.5GB,           PML4:261]
+ *  0xffff82d0c0000000 - 0xffff82ffffffffff [189GB,             PML4:261]
  *    Reserved for future use.
- *  0xffff82ffe0000000 - 0xffff82ffffffffff [512MB, 2^29 bytes, PML4:261]
- *    Super-page information array.
  *  0xffff830000000000 - 0xffff847fffffffff [1.5TB, 3*2^39 bytes, PML4:262-264]
  *    Page-frame information array.
  *  0xffff848000000000 - 0xffff87ffffffffff [3.5TB, 7*2^39 bytes, PML4:265-271]
@@ -230,14 +226,6 @@  extern unsigned char boot_edid_info[128];
 #define XEN_VIRT_START          (HIRO_COMPAT_MPT_VIRT_END)
 #define XEN_VIRT_END            (XEN_VIRT_START + GB(1))
 
-/* Slot 261: superpage information array (64MB or 512MB). */
-#define SPAGETABLE_VIRT_END     FRAMETABLE_VIRT_START
-#define SPAGETABLE_NR           (((FRAMETABLE_NR - 1) >> (SUPERPAGE_SHIFT - \
-                                                          PAGE_SHIFT)) + 1)
-#define SPAGETABLE_SIZE         (SPAGETABLE_NR * sizeof(struct spage_info))
-#define SPAGETABLE_VIRT_START   ((SPAGETABLE_VIRT_END - SPAGETABLE_SIZE) & \
-                                 (_AC(-1,UL) << SUPERPAGE_SHIFT))
-
 #ifndef CONFIG_BIGMEM
 /* Slot 261: page-frame information array (128GB). */
 #define FRAMETABLE_SIZE         GB(128)
diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index 2550e35f85..2bf3f335ad 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -233,21 +233,6 @@  struct page_info
 #define PGC_count_width   PG_shift(9)
 #define PGC_count_mask    ((1UL<<PGC_count_width)-1)
 
-struct spage_info
-{
-       unsigned long type_info;
-};
-
- /* The following page types are MUTUALLY EXCLUSIVE. */
-#define SGT_none          PG_mask(0, 2)  /* superpage not in use */
-#define SGT_mark          PG_mask(1, 2)  /* Marked as a superpage */
-#define SGT_dynamic       PG_mask(2, 2)  /* has been dynamically mapped as a superpage */
-#define SGT_type_mask     PG_mask(3, 2)  /* Bits 30-31 or 62-63. */
-
- /* Count of uses of this superpage as its current type. */
-#define SGT_count_width   PG_shift(3)
-#define SGT_count_mask    ((1UL<<SGT_count_width)-1)
-
 #define is_xen_heap_page(page) ((page)->count_info & PGC_xen_heap)
 #define is_xen_heap_mfn(mfn) \
     (__mfn_valid(mfn) && is_xen_heap_page(__mfn_to_page(mfn)))
@@ -282,8 +267,6 @@  extern void share_xen_page_with_privileged_guests(
 extern void free_shared_domheap_page(struct page_info *page);
 
 #define frame_table ((struct page_info *)FRAMETABLE_VIRT_START)
-#define spage_table ((struct spage_info *)SPAGETABLE_VIRT_START)
-int get_superpage(unsigned long mfn, struct domain *d);
 extern unsigned long max_page;
 extern unsigned long total_pages;
 void init_frametable(void);
@@ -329,8 +312,6 @@  void zap_ro_mpt(unsigned long mfn);
 
 bool is_iomem_page(mfn_t mfn);
 
-void clear_superpage_mark(struct page_info *page);
-
 const unsigned long *get_platform_badpages(unsigned int *array_size);
 /* Per page locks:
  * page_lock() is used for two purposes: pte serialization, and memory sharing.
@@ -403,7 +384,6 @@  static inline int get_page_and_type(struct page_info *page,
 
 int check_descriptor(const struct domain *, struct desc_struct *d);
 
-extern bool opt_allow_superpage;
 extern paddr_t mem_hotplug;
 
 /******************************************************************************
diff --git a/xen/include/asm-x86/page.h b/xen/include/asm-x86/page.h
index 474b9bde78..0f843c2a46 100644
--- a/xen/include/asm-x86/page.h
+++ b/xen/include/asm-x86/page.h
@@ -239,15 +239,6 @@  void copy_page_sse2(void *, const void *);
 #define __pfn_to_paddr(pfn) ((paddr_t)(pfn) << PAGE_SHIFT)
 #define __paddr_to_pfn(pa)  ((unsigned long)((pa) >> PAGE_SHIFT))
 
-
-/* Convert between machine frame numbers and spage-info structures. */
-#define __mfn_to_spage(mfn)  (spage_table + pfn_to_sdx(mfn))
-#define __spage_to_mfn(pg)   sdx_to_pfn((unsigned long)((pg) - spage_table))
-
-/* Convert between page-info structures and spage-info structures. */
-#define page_to_spage(page)  (spage_table+(((page)-frame_table)>>(SUPERPAGE_SHIFT-PAGE_SHIFT)))
-#define spage_to_page(spage)  (frame_table+(((spage)-spage_table)<<(SUPERPAGE_SHIFT-PAGE_SHIFT)))
-
 /*
  * We define non-underscored wrappers for above conversion functions. These are
  * overridden in various source files while underscored versions remain intact.
@@ -259,8 +250,6 @@  void copy_page_sse2(void *, const void *);
 #define maddr_to_virt(ma)   __maddr_to_virt((unsigned long)(ma))
 #define mfn_to_page(mfn)    __mfn_to_page(mfn)
 #define page_to_mfn(pg)     __page_to_mfn(pg)
-#define mfn_to_spage(mfn)    __mfn_to_spage(mfn)
-#define spage_to_mfn(pg)     __spage_to_mfn(pg)
 #define maddr_to_page(ma)   __maddr_to_page(ma)
 #define page_to_maddr(pg)   __page_to_maddr(pg)
 #define virt_to_page(va)    __virt_to_page(va)
diff --git a/xen/include/asm-x86/paging.h b/xen/include/asm-x86/paging.h
index 44e86d6a1f..64bf2f968a 100644
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -371,8 +371,7 @@  static inline unsigned int paging_max_paddr_bits(const struct domain *d)
 {
     unsigned int bits = paging_mode_hap(d) ? hap_paddr_bits : paddr_bits;
 
-    if ( !IS_ENABLED(BIGMEM) && paging_mode_shadow(d) &&
-         (!is_pv_domain(d) || opt_allow_superpage) )
+    if ( !IS_ENABLED(BIGMEM) && paging_mode_shadow(d) && !is_pv_domain(d) )
     {
         /* Shadowed superpages store GFNs in 32-bit page_info fields. */
         bits = min(bits, 32U + PAGE_SHIFT);
diff --git a/xen/include/asm-x86/x86_64/page.h b/xen/include/asm-x86/x86_64/page.h
index 31ba975e3d..1b48309363 100644
--- a/xen/include/asm-x86/x86_64/page.h
+++ b/xen/include/asm-x86/x86_64/page.h
@@ -41,8 +41,6 @@ 
 
 extern unsigned long xen_virt_end;
 
-#define spage_to_pdx(spg) (((spg) - spage_table)<<(SUPERPAGE_SHIFT-PAGE_SHIFT))
-#define pdx_to_spage(pdx) (spage_table + ((pdx)>>(SUPERPAGE_SHIFT-PAGE_SHIFT)))
 /*
  * Note: These are solely for the use by page_{get,set}_owner(), and
  *       therefore don't need to handle the XEN_VIRT_{START,END} range.