xen: Complete pagetable pinning

Xen requires all active pagetables to be marked read-only.  When the
base of the pagetable is loaded into %cr3, the hypervisor validates
the entire pagetable and only allows the load to proceed if it all
checks out.

This is pretty slow, so to mitigate this cost Xen has a notion of
pinned pagetables.  Pinned pagetables are pagetables which are
considered to be active even if no processor's cr3 is pointing to is.
This means that it must remain read-only and all updates are validated
by the hypervisor.  This makes context switches much cheaper, because
the hypervisor doesn't need to revalidate the pagetable each time.

This also adds a new paravirt hook which is called during setup once
the zones and memory allocator have been initialized.  When the
init_mm pagetable is first built, the struct page array does not yet
exist, and so there's nowhere to put he init_mm pagetable's PG_pinned
flags.  Once the zones are initialized and the struct page array
exists, we can set the PG_pinned flags for those pages.

This patch also adds the Xen support for pte pages allocated out of
highmem (highpte) by implementing xen_kmap_atomic_pte.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Cc: Zach Amsden <zach@vmware.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/i386/xen/xen-ops.h b/arch/i386/xen/xen-ops.h
index 79648fe1ab77..54d98b52085e 100644
--- a/arch/i386/xen/xen-ops.h
+++ b/arch/i386/xen/xen-ops.h
@@ -20,6 +20,8 @@ unsigned long xen_get_wallclock(void);
 int xen_set_wallclock(unsigned long time);
 cycle_t xen_clocksource_read(void);
 
+void xen_mark_init_mm_pinned(void);
+
 DECLARE_PER_CPU(enum paravirt_lazy_mode, xen_lazy_mode);
 
 static inline unsigned xen_get_lazy_mode(void)