Without a fix for this 2.6.39-rc5 fails during bootup.
It fails such early, you only Xen telling you that the domain crashed.
There is one patch to fix this, and the last word was here:
http://marc.info/?i=4DAF0ECB.8060009@xxxxxxxx
But after nothing had been heard from Peter.
So I decided to look at this from a different perspective: why not
contain the workaround inside Xen early bootup code.
I've tested this code as DomU (1G, 2G, 3G), Dom0 (8G, 4G, 1000M)
and they all booted fine. Hadn't compile tested it on 32-bit and
I think it will actually complain about it. Let me fix that.
See attached patch (also present in stable/bug-fixes-for-rc5) which also
has the "xen: mask_rw_pte mark RO all pagetable pages up to pgt_buf_top"
integrated in.
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index aef7af9..a54c7c2 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1463,6 +1463,115 @@ static int xen_pgd_alloc(struct mm_struct *mm)
return ret;
}
+#ifdef CONFIG_X86_64
+static __initdata u64 __last_pgt_set_rw = 0;
+static __initdata u64 __pgt_buf_start = 0;
+static __initdata u64 __pgt_buf_end = 0;
+static __initdata u64 __pgt_buf_top = 0;
+/*
+ * As a consequence of the commit:
+ *
+ * commit 4b239f458c229de044d6905c2b0f9fe16ed9e01e
+ * Author: Yinghai Lu <yinghai@xxxxxxxxxx>
+ * Date: Fri Dec 17 16:58:28 2010 -0800
+ *
+ * x86-64, mm: Put early page table high
+ *
+ * at some point init_memory_mapping is going to reach the pagetable pages
+ * area and map those pages too (mapping them as normal memory that falls
+ * in the range of addresses passed to init_memory_mapping as argument).
+ * Some of those pages are already pagetable pages (they are in the range
+ * pgt_buf_start-pgt_buf_end) therefore they are going to be mapped RO and
+ * everything is fine.
+ * Some of these pages are not pagetable pages yet (they fall in the range
+ * pgt_buf_end-pgt_buf_top; for example the page at pgt_buf_end) so they
+ * are going to be mapped RW. When these pages become pagetable pages and
+ * are hooked into the pagetable, xen will find that the guest has already
+ * a RW mapping of them somewhere and fail the operation.
+ * The reason Xen requires pagetables to be RO is that the hypervisor needs
+ * to verify that the pagetables are valid before using them. The validation
+ * operations are called "pinning" (more details in arch/x86/xen/mmu.c).
+ *
+ * In order to fix the issue we mark all the pages in the entire range
+ * pgt_buf_start-pgt_buf_top as RO, however when the pagetable allocation
+ * is completed only the range pgt_buf_start-pgt_buf_end is reserved by
+ * init_memory_mapping. Hence the kernel is going to crash as soon as one
+ * of the pages in the range pgt_buf_end-pgt_buf_top is reused (b/c those
+ * ranges are RO).
+ *
+ * For this reason, this function is introduced which is called _after_
+ * the init_memory_mapping has completed (in a perfect world we would
+ * call this function from init_memory_mapping, but lets ignore that).
+ *
+ * Because we are called _after_ init_memory_mapping the pgt_buf_[start,
+ * end,top] have all changed to new values (b/c another init_memory_mapping
+ * is called). Hence, the first time we enter this function, we save
+ * away the pgt_buf_start value and update the pgt_buf_[end,top].
+ *
+ * When we detect that the "old" pgt_buf_start through pgt_buf_end
+ * PFNs have been reserved (so memblock_x86_reserve_range has been called),
+ * we immediately set out to RW the "old" pgt_buf_end through pgt_buf_top.
+ *
+ * And then we update those "old" pgt_buf_[end|top] with the new ones
+ * so that we can redo this on the next pagetable.
+ */
+static __init void mark_rw_past_pgt(unsigned long pfn) {
+
+ if (pfn && pgt_buf_end > pgt_buf_start) {
+ u64 addr, size;
+
+ /* Save it away. */
+ if (!__pgt_buf_start) {
+ __pgt_buf_start = pgt_buf_start;
+ __pgt_buf_end = pgt_buf_end;
+ __pgt_buf_top = pgt_buf_top;
+ return;
+ }
+ /* If we get the range that starts at __pgt_buf_end that means
+ * the range is reserved, and that in 'init_memory_mapping'
+ * the 'memblock_x86_reserve_range' has been called with the
+ * outdated __pgt_buf_start, __pgt_buf_end (the "new"
+ * pgt_buf_[start|end|top] refer now to a new pagetable.
+ * Note: we are called _after_ the pgt_buf_[..] have been
+ * updated.*/
+
+ addr =
memblock_x86_find_in_range_size(PFN_PHYS(__pgt_buf_start), &size, PAGE_SIZE);
+
+ /* Still not reserved, meaning 'memblock_x86_reserve_range'
+ * hasn't been called yet. Update the _end and _top.*/
+ if (addr == PFN_PHYS(__pgt_buf_start)) {
+ __pgt_buf_end = pgt_buf_end;
+ __pgt_buf_top = pgt_buf_top;
+ return;
+ }
+
+ /* OK, the area is reserved, meaning it is time for us to
+ * set RW for the old end->top PFNs. */
+
+ /* ..unless we had already done this. */
+ if (__pgt_buf_end == __last_pgt_set_rw)
+ return;
+
+ addr = PFN_PHYS(__pgt_buf_end);
+
+ /* set as RW the rest */
+ printk(KERN_DEBUG "xen: setting RW the range %llx - %llx\n",
+ PFN_PHYS(__pgt_buf_end), PFN_PHYS(__pgt_buf_top));
+
+ while (addr < PFN_PHYS(__pgt_buf_top)) {
+ make_lowmem_page_readwrite(__va(addr));
+ addr += PAGE_SIZE;
+ }
+ /* And update everything so that we are ready for the next
+ * pagetable (the one created for regions past 4GB) */
+ __last_pgt_set_rw = __pgt_buf_end;
+ __pgt_buf_start = pgt_buf_start;
+ __pgt_buf_end = pgt_buf_end;
+ __pgt_buf_top = pgt_buf_top;
+ }
+ return;
+}
+#endif
static void xen_pgd_free(struct mm_struct *mm, pgd_t *pgd)
{
#ifdef CONFIG_X86_64
@@ -1488,6 +1597,7 @@ static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
{
unsigned long pfn = pte_pfn(pte);
+ mark_rw_past_pgt(pfn);
/*
* If the new pfn is within the range of the newly allocated
* kernel pagetable, and it isn't being mapped into an
@@ -1495,7 +1605,7 @@ static __init pte_t mask_rw_pte(pte_t *ptep, pte_t pte)
* it is RO.
*/
if (((!is_early_ioremap_ptep(ptep) &&
- pfn >= pgt_buf_start && pfn < pgt_buf_end)) ||
+ pfn >= pgt_buf_start && pfn < pgt_buf_top)) ||
(is_early_ioremap_ptep(ptep) && pfn != (pgt_buf_end -
1)))
pte = pte_wrprotect(pte);
@@ -1997,6 +2107,8 @@ __init void xen_ident_map_ISA(void)
static __init void xen_post_allocator_init(void)
{
+ mark_rw_past_pgt(1);
+
#ifdef CONFIG_XEN_DEBUG
pv_mmu_ops.make_pte = PV_CALLEE_SAVE(xen_make_pte_debug);
#endif
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