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@@ -1463,6 +1463,119 @@ static int xen_pgd_alloc(struct mm_struct *mm)
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return ret;
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}
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+#ifdef CONFIG_X86_64
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+static __initdata u64 __last_pgt_set_rw = 0;
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+static __initdata u64 __pgt_buf_start = 0;
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+static __initdata u64 __pgt_buf_end = 0;
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+static __initdata u64 __pgt_buf_top = 0;
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+/*
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+ * As a consequence of the commit:
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+ *
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+ * commit 4b239f458c229de044d6905c2b0f9fe16ed9e01e
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+ * Author: Yinghai Lu <yinghai@kernel.org>
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+ * Date: Fri Dec 17 16:58:28 2010 -0800
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+ *
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+ * x86-64, mm: Put early page table high
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+ *
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+ * at some point init_memory_mapping is going to reach the pagetable pages
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+ * area and map those pages too (mapping them as normal memory that falls
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+ * in the range of addresses passed to init_memory_mapping as argument).
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+ * Some of those pages are already pagetable pages (they are in the range
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+ * pgt_buf_start-pgt_buf_end) therefore they are going to be mapped RO and
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+ * everything is fine.
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+ * Some of these pages are not pagetable pages yet (they fall in the range
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+ * pgt_buf_end-pgt_buf_top; for example the page at pgt_buf_end) so they
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+ * are going to be mapped RW. When these pages become pagetable pages and
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+ * are hooked into the pagetable, xen will find that the guest has already
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+ * a RW mapping of them somewhere and fail the operation.
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+ * The reason Xen requires pagetables to be RO is that the hypervisor needs
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+ * to verify that the pagetables are valid before using them. The validation
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+ * operations are called "pinning".
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+ *
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+ * In order to fix the issue we mark all the pages in the entire range
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+ * pgt_buf_start-pgt_buf_top as RO, however when the pagetable allocation
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+ * is completed only the range pgt_buf_start-pgt_buf_end is reserved by
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+ * init_memory_mapping. Hence the kernel is going to crash as soon as one
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+ * of the pages in the range pgt_buf_end-pgt_buf_top is reused (b/c those
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+ * ranges are RO).
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+ *
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+ * For this reason, 'mark_rw_past_pgt' is introduced which is called _after_
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+ * the init_memory_mapping has completed (in a perfect world we would
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+ * call this function from init_memory_mapping, but lets ignore that).
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+ *
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+ * Because we are called _after_ init_memory_mapping the pgt_buf_[start,
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+ * end,top] have all changed to new values (b/c init_memory_mapping
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+ * is called and setting up another new page-table). Hence, the first time
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+ * we enter this function, we save away the pgt_buf_start value and update
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+ * the pgt_buf_[end,top].
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+ *
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+ * When we detect that the "old" pgt_buf_start through pgt_buf_end
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+ * PFNs have been reserved (so memblock_x86_reserve_range has been called),
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+ * we immediately set out to RW the "old" pgt_buf_end through pgt_buf_top.
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+ *
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+ * And then we update those "old" pgt_buf_[end|top] with the new ones
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+ * so that we can redo this on the next pagetable.
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+ */
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+static __init void mark_rw_past_pgt(void) {
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+
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+ if (pgt_buf_end > pgt_buf_start) {
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+ u64 addr, size;
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+
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+ /* Save it away. */
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+ if (!__pgt_buf_start) {
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+ __pgt_buf_start = pgt_buf_start;
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+ __pgt_buf_end = pgt_buf_end;
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+ __pgt_buf_top = pgt_buf_top;
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+ return;
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+ }
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+ /* If we get the range that starts at __pgt_buf_end that means
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+ * the range is reserved, and that in 'init_memory_mapping'
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+ * the 'memblock_x86_reserve_range' has been called with the
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+ * outdated __pgt_buf_start, __pgt_buf_end (the "new"
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+ * pgt_buf_[start|end|top] refer now to a new pagetable.
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+ * Note: we are called _after_ the pgt_buf_[..] have been
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+ * updated.*/
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+
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+ addr = memblock_x86_find_in_range_size(PFN_PHYS(__pgt_buf_start),
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+ &size, PAGE_SIZE);
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+
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+ /* Still not reserved, meaning 'memblock_x86_reserve_range'
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+ * hasn't been called yet. Update the _end and _top.*/
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+ if (addr == PFN_PHYS(__pgt_buf_start)) {
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+ __pgt_buf_end = pgt_buf_end;
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+ __pgt_buf_top = pgt_buf_top;
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+ return;
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+ }
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+
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+ /* OK, the area is reserved, meaning it is time for us to
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+ * set RW for the old end->top PFNs. */
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+
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+ /* ..unless we had already done this. */
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+ if (__pgt_buf_end == __last_pgt_set_rw)
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+ return;
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+
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+ addr = PFN_PHYS(__pgt_buf_end);
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+
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+ /* set as RW the rest */
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+ printk(KERN_DEBUG "xen: setting RW the range %llx - %llx\n",
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+ PFN_PHYS(__pgt_buf_end), PFN_PHYS(__pgt_buf_top));
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+
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+ while (addr < PFN_PHYS(__pgt_buf_top)) {
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+ make_lowmem_page_readwrite(__va(addr));
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+ addr += PAGE_SIZE;
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+ }
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+ /* And update everything so that we are ready for the next
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+ * pagetable (the one created for regions past 4GB) */
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+ __last_pgt_set_rw = __pgt_buf_end;
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+ __pgt_buf_start = pgt_buf_start;
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+ __pgt_buf_end = pgt_buf_end;
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+ __pgt_buf_top = pgt_buf_top;
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+ }
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+ return;
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+}
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+#else
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+static __init void mark_rw_past_pgt(void) { }
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+#endif
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static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd)
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{
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#ifdef CONFIG_X86_64
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@@ -1488,6 +1601,14 @@ static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
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{
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unsigned long pfn = pte_pfn(pte);
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+ /*
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+ * A bit of optimization. We do not need to call the workaround
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+ * when xen_set_pte_init is called with a PTE with 0 as PFN.
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+ * That is b/c the pagetable at that point are just being populated
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+ * with empty values and we can save some cycles by not calling
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+ * the 'memblock' code.*/
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+ if (pfn)
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+ mark_rw_past_pgt();
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/*
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* If the new pfn is within the range of the newly allocated
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* kernel pagetable, and it isn't being mapped into an
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@@ -1495,7 +1616,7 @@ static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
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* it is RO.
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*/
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if (((!is_early_ioremap_ptep(ptep) &&
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- pfn >= pgt_buf_start && pfn < pgt_buf_end)) ||
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+ pfn >= pgt_buf_start && pfn < pgt_buf_top)) ||
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(is_early_ioremap_ptep(ptep) && pfn != (pgt_buf_end - 1)))
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pte = pte_wrprotect(pte);
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@@ -1997,6 +2118,8 @@ __init void xen_ident_map_ISA(void)
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static __init void xen_post_allocator_init(void)
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{
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+ mark_rw_past_pgt();
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+
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#ifdef CONFIG_XEN_DEBUG
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pv_mmu_ops.make_pte = PV_CALLEE_SAVE(xen_make_pte_debug);
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#endif
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