[PATCH] i386: PARAVIRT: add kmap_atomic_pte for mapping highpte pages

Xen and VMI both have special requirements when mapping a highmem pte
page into the kernel address space.  These can be dealt with by adding
a new kmap_atomic_pte() function for mapping highptes, and hooking it
into the paravirt_ops infrastructure.

Xen specifically wants to map the pte page RO, so this patch exposes a
helper function, kmap_atomic_prot, which maps the page with the
specified page protections.

This also adds a kmap_flush_unused() function to clear out the cached
kmap mappings.  Xen needs this to clear out any potential stray RW
mappings of pages which will become part of a pagetable.

[ Zach - vmi.c will need some attention after this patch.  It wasn't
  immediately obvious to me what needs to be done. ]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Zachary Amsden <zach@vmware.com>

2 files changed, 12 insertions, 2 deletions

diff --git a/arch/i386/kernel/paravirt.c b/arch/i386/kernel/paravirt.c
index 13f41b5c887a..596f382c641c 100644
--- a/arch/i386/kernel/paravirt.c
+++ b/arch/i386/kernel/paravirt.c
@@ -20,6 +20,7 @@
 #include <linux/efi.h>
 #include <linux/bcd.h>
 #include <linux/start_kernel.h>
+#include <linux/highmem.h>
 
 #include <asm/bug.h>
 #include <asm/paravirt.h>
@@ -316,6 +317,10 @@ struct paravirt_ops paravirt_ops = {
 
         .ptep_get_and_clear = native_ptep_get_and_clear,
 
+#ifdef CONFIG_HIGHPTE
+        .kmap_atomic_pte = kmap_atomic,
+#endif
+
 #ifdef CONFIG_X86_PAE
         .set_pte_atomic = native_set_pte_atomic,
         .set_pte_present = native_set_pte_present,
diff --git a/arch/i386/mm/highmem.c b/arch/i386/mm/highmem.c
index ac70d09df7ee..a1a21abf742e 100644
--- a/arch/i386/mm/highmem.c
+++ b/arch/i386/mm/highmem.c
@@ -26,7 +26,7 @@ void kunmap(struct page *page)
  * However when holding an atomic kmap is is not legal to sleep, so atomic
  * kmaps are appropriate for short, tight code paths only.
  */
-void *kmap_atomic(struct page *page, enum km_type type)
+void *kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot)
 {
         enum fixed_addresses idx;
         unsigned long vaddr;
@@ -41,12 +41,17 @@ void *kmap_atomic(struct page *page, enum km_type type)
                 return page_address(page);
 
         vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
-        set_pte(kmap_pte-idx, mk_pte(page, kmap_prot));
+        set_pte(kmap_pte-idx, mk_pte(page, prot));
         arch_flush_lazy_mmu_mode();
 
         return (void*) vaddr;
 }
 
+void *kmap_atomic(struct page *page, enum km_type type)
+{
+        return kmap_atomic_prot(page, type, kmap_prot);
+}
+
 void kunmap_atomic(void *kvaddr, enum km_type type)
 {
         unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;