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>
==================================================================---
a/arch/i386/mm/highmem.c
+++ b/arch/i386/mm/highmem.c
@@ -44,22 +44,19 @@ void *kmap_atomic(struct page *page, enu
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();
@@ -68,14 +65,14 @@ void kunmap_atomic(void *kvaddr, enum km
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();
@@ -94,7 +91,6 @@ void *kmap_atomic_pfn(unsigned long pfn,
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;
}
==================================================================---
a/include/asm-i386/pgtable.h
+++ b/include/asm-i386/pgtable.h
@@ -441,6 +441,13 @@ extern pte_t *lookup_address(unsigned lo
#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.