Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dledford/rdma

[linux-2.6-block.git] / arch / x86 / xen / enlighten.c

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 0b95c9b8283fe2afe885d9a8ae98393c14ecc498..11d6fb4e8483d529f833cbc1276ea4ffd3c68102 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -483,6 +483,7 @@ static void set_aliased_prot(void *v, pgprot_t prot)
        pte_t pte;
        unsigned long pfn;
        struct page *page;
+       unsigned char dummy;
 
        ptep = lookup_address((unsigned long)v, &level);
        BUG_ON(ptep == NULL);
@@ -492,6 +493,32 @@ static void set_aliased_prot(void *v, pgprot_t prot)
 
        pte = pfn_pte(pfn, prot);
 
+       /*
+        * Careful: update_va_mapping() will fail if the virtual address
+        * we're poking isn't populated in the page tables.  We don't
+        * need to worry about the direct map (that's always in the page
+        * tables), but we need to be careful about vmap space.  In
+        * particular, the top level page table can lazily propagate
+        * entries between processes, so if we've switched mms since we
+        * vmapped the target in the first place, we might not have the
+        * top-level page table entry populated.
+        *
+        * We disable preemption because we want the same mm active when
+        * we probe the target and when we issue the hypercall.  We'll
+        * have the same nominal mm, but if we're a kernel thread, lazy
+        * mm dropping could change our pgd.
+        *
+        * Out of an abundance of caution, this uses __get_user() to fault
+        * in the target address just in case there's some obscure case
+        * in which the target address isn't readable.
+        */
+
+       preempt_disable();
+
+       pagefault_disable();    /* Avoid warnings due to being atomic. */
+       __get_user(dummy, (unsigned char __user __force *)v);
+       pagefault_enable();
+
        if (HYPERVISOR_update_va_mapping((unsigned long)v, pte, 0))
                BUG();
 
@@ -503,6 +530,8 @@ static void set_aliased_prot(void *v, pgprot_t prot)
                                BUG();
        } else
                kmap_flush_unused();
+
+       preempt_enable();
 }
 
 static void xen_alloc_ldt(struct desc_struct *ldt, unsigned entries)
@@ -510,6 +539,17 @@ static void xen_alloc_ldt(struct desc_struct *ldt, unsigned entries)
        const unsigned entries_per_page = PAGE_SIZE / LDT_ENTRY_SIZE;
        int i;
 
+       /*
+        * We need to mark the all aliases of the LDT pages RO.  We
+        * don't need to call vm_flush_aliases(), though, since that's
+        * only responsible for flushing aliases out the TLBs, not the
+        * page tables, and Xen will flush the TLB for us if needed.
+        *
+        * To avoid confusing future readers: none of this is necessary
+        * to load the LDT.  The hypervisor only checks this when the
+        * LDT is faulted in due to subsequent descriptor access.
+        */
+
        for(i = 0; i < entries; i += entries_per_page)
                set_aliased_prot(ldt + i, PAGE_KERNEL_RO);
 }