On Fri, Sep 07, 2018 at 12:52:17PM +0200, Thomas Gleixner wrote:
> On Fri, 7 Sep 2018, Feng Tang wrote:
> > On Fri, Aug 31, 2018 at 09:36:59PM +0800, Feng Tang wrote:
> > > Any sugestion? I can only have patch like this:
> >
> > Could you review this patch, as at this time window there is no usable
> > memory
> > block or other memory allocators that I know, so I follow the exisitng
> > static
> > fixmap page table code and add one more.
>
> You really want to add a proper sanity check for this. The static stuff has
> to cover the fixmap. Just making it work for this particular case is sloppy
> at best as the next larger change of the fixmap will just bring the problem
> back.
Yes, agree.
Since the issue happens very early before any serial console, I can only think
of a build time check.
Thanks,
Feng
---
arch/x86/kernel/head_64.S | 6 +++++-
arch/x86/mm/pgtable.c | 13 +++++++++++++
2 files changed, 18 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 15ebc2fc166e..3a1d33b43c29 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -448,11 +448,15 @@ NEXT_PAGE(level2_fixmap_pgt)
.fill 506,8,0
.quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
/* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
- .fill 5,8,0
+ .quad level1_fixmap_pgt1 - __START_KERNEL_map + _PAGE_TABLE_NOENC
+ .fill 4,8,0
NEXT_PAGE(level1_fixmap_pgt)
.fill 512,8,0
+NEXT_PAGE(level1_fixmap_pgt1)
+ .fill 512,8,0
+
#undef PMDS
.data
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index e848a4811785..fc172551048a 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -637,6 +637,19 @@ void __native_set_fixmap(enum fixed_addresses idx, pte_t
pte)
{
unsigned long address = __fix_to_virt(idx);
+#ifdef CONFIG_X86_64
+ /*
+ * In arch/x86/kernel/head_64.S, the static page table
+ * has been setup for 4M space [-12M, -8M]
+ * 0xFFFFFFFFFF400000 ~ 0xFFFFFFFFFF7FFFFF
+ * Add a sanity check whether fixed_address crosses
+ * the boundary.
+ */
+ #define FIXMAP_STATIC_PGTABLE_START 0xFFFFFFFFFF400000
+ BUILD_BUG_ON(__fix_to_virt(__end_of_permanent_fixed_addresses)
+ < FIXMAP_STATIC_PGTABLE_START);
+#endif
+
if (idx >= __end_of_fixed_addresses) {
BUG();
return;
--
2.14.1
>
> Thanks,
>
> tglx
