[PATCH] paravirt: kpte flush

Create a new PTE function which combines clearing a kernel PTE with the
subsequent flush.  This allows the two to be easily combined into a single
hypercall or paravirt-op.  More subtly, reverse the order of the flush for
kmap_atomic.  Instead of flushing on establishing a mapping, flush on clearing
a mapping.  This eliminates the possibility of leaving stale kmap entries
which may still have valid TLB mappings.  This is required for direct mode
hypervisors, which need to reprotect all mappings of a given page when
changing the page type from a normal page to a protected page (such as a page
table or descriptor table page).  But it also provides some nicer semantics
for real hardware, by providing extra debug-proofing against using stale
mappings, as well as ensuring that no stale mappings exist when changing the
cacheability attributes of a page, which could lead to cache conflicts when
two different types of mappings exist for the same page.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/arch/i386/mm/highmem.c b/arch/i386/mm/highmem.c
index ba44000..f9f647c 100644 (file)
--- a/arch/i386/mm/highmem.c
+++ b/arch/i386/mm/highmem.c
@@ -38,22 +38,19 @@ void *kmap_atomic(struct page *page, enum km_type type)
 
        idx = type + KM_TYPE_NR*smp_processor_id();
        vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
-#ifdef CONFIG_DEBUG_HIGHMEM
        if (!pte_none(*(kmap_pte-idx)))
                BUG();
-#endif
        set_pte(kmap_pte-idx, mk_pte(page, kmap_prot));
-       __flush_tlb_one(vaddr);
 
        return (void*) vaddr;
 }
 
 void kunmap_atomic(void *kvaddr, enum km_type type)
 {
-#ifdef CONFIG_DEBUG_HIGHMEM
        unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
        enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();
 
+#ifdef CONFIG_DEBUG_HIGHMEM
        if (vaddr >= PAGE_OFFSET && vaddr < (unsigned long)high_memory) {
                dec_preempt_count();
                preempt_check_resched();
@@ -62,14 +59,14 @@ void kunmap_atomic(void *kvaddr, enum km_type type)
 
        if (vaddr != __fix_to_virt(FIX_KMAP_BEGIN+idx))
                BUG();
-
+#endif
        /*
-        * force other mappings to Oops if they'll try to access
-        * this pte without first remap it
+        * Force other mappings to Oops if they'll try to access this pte
+        * without first remap it.  Keeping stale mappings around is a bad idea
+        * also, in case the page changes cacheability attributes or becomes
+        * a protected page in a hypervisor.
         */
-       pte_clear(&init_mm, vaddr, kmap_pte-idx);
-       __flush_tlb_one(vaddr);
-#endif
+       kpte_clear_flush(kmap_pte-idx, vaddr);
 
        dec_preempt_count();
        preempt_check_resched();
@@ -88,7 +85,6 @@ void *kmap_atomic_pfn(unsigned long pfn, enum km_type type)
        idx = type + KM_TYPE_NR*smp_processor_id();
        vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
        set_pte(kmap_pte-idx, pfn_pte(pfn, kmap_prot));
-       __flush_tlb_one(vaddr);
 
        return (void*) vaddr;
 }

diff --git a/include/asm-i386/pgtable.h b/include/asm-i386/pgtable.h
index 94c87ff..ee9696d 100644 (file)
--- a/include/asm-i386/pgtable.h
+++ b/include/asm-i386/pgtable.h
@@ -441,6 +441,13 @@ extern pte_t *lookup_address(unsigned long address);
 #define pte_unmap_nested(pte) do { } while (0)
 #endif
 
+/* Clear a kernel PTE and flush it from the TLB */
+#define kpte_clear_flush(ptep, vaddr)                                  \
+do {                                                                   \
+       pte_clear(&init_mm, vaddr, ptep);                               \
+       __flush_tlb_one(vaddr);                                         \
+} while (0)
+
 /*
  * The i386 doesn't have any external MMU info: the kernel page
  * tables contain all the necessary information.