x86: Speed up PV-guest superpage mapping

The current version of superpage mapping takes a PGT_writable
reference to every page in a superpage each time it is mapped.  This
is extremely slow, so slow that applications become unusable.

My solution for this is to introduce a superpage table in the
hypervisor, similar to the frametable structure for pages.  Currently
this table only has a type_info element.  There are three types a
superpage can have, SGT_mark, SGT_dynamic, or SGT_none.

In normal operation, the first time a superpage is mapped, a
PGT_writable reference is taken to each page in the superpage, and the
superpage is set to type SGT_dynamic and the superpage typecount is
incremented.  On subsequent mappings and unmappings, only the
superpage typecount changes.  On the last unmap, the PGT_writable
reference on each page is removed.

The SGT_mark type is set and cleared through two new MMUEXT
hypercalls, mark_super and unmark_super.  When the hypercall is made,
the superpage's type is set to SGT_mark and a PGT_writable reference
is taken to its pages.  On unmark, the type is cleared and the
reference removed.

If a page is already set to SGT_dynamic when mark_super is called, the
type is changed to SGT_mark and no additional PGT_writable reference
is taken.  If there are still outstanding mappings of this superpage
when unmark_super is called, the type is set to SGT_dynamic and the
PGT_writable reference is not removed.

Fast superpage mapping is only supported on 64 bit hypervisors.  For
32 bit hyperviors, superpage mapping is supported but will be
extremely slow.

Signed-off-by: Dave McCracken <dave.mccracken@oracle.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/xen/include/asm-x86/x86_64/page.h b/xen/include/asm-x86/x86_64/page.h
index f1448c12a8..2e61709e29 100644
--- a/xen/include/asm-x86/x86_64/page.h
+++ b/xen/include/asm-x86/x86_64/page.h
@@ -7,6 +7,7 @@
 #define L3_PAGETABLE_SHIFT      30
 #define L4_PAGETABLE_SHIFT      39
 #define PAGE_SHIFT              L1_PAGETABLE_SHIFT
+#define SUPERPAGE_SHIFT         L2_PAGETABLE_SHIFT
 #define ROOT_PAGETABLE_SHIFT    L4_PAGETABLE_SHIFT
 
 #define PAGETABLE_ORDER         9
@@ -15,6 +16,7 @@
 #define L3_PAGETABLE_ENTRIES    (1<<PAGETABLE_ORDER)
 #define L4_PAGETABLE_ENTRIES    (1<<PAGETABLE_ORDER)
 #define ROOT_PAGETABLE_ENTRIES  L4_PAGETABLE_ENTRIES
+#define SUPERPAGE_ORDER         PAGETABLE_ORDER
 
 #define __PAGE_OFFSET           DIRECTMAP_VIRT_START
 #define __XEN_VIRT_START        XEN_VIRT_START
@@ -41,6 +43,8 @@ extern void pfn_pdx_hole_setup(unsigned long);
 
 #define page_to_pdx(pg)  ((pg) - frame_table)
 #define pdx_to_page(pdx) (frame_table + (pdx))
+#define spage_to_pdx(spg) ((spg>>(SUPERPAGE_SHIFT-PAGE_SHIFT)) - spage_table)
+#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.
@@ -64,6 +68,16 @@ static inline unsigned long pdx_to_pfn(unsigned long pdx)
            ((pdx << pfn_pdx_hole_shift) & pfn_top_mask);
 }
 
+static inline unsigned long pfn_to_sdx(unsigned long pfn)
+{
+    return pfn_to_pdx(pfn) >> (SUPERPAGE_SHIFT-PAGE_SHIFT);
+}
+
+static inline unsigned long sdx_to_pfn(unsigned long sdx)
+{
+    return pdx_to_pfn(sdx << (SUPERPAGE_SHIFT-PAGE_SHIFT));
+}
+
 static inline unsigned long __virt_to_maddr(unsigned long va)
 {
     ASSERT(va >= XEN_VIRT_START);