MIPS: Avoid mcheck by flushing page range in huge_ptep_set_access_flags()
Problem:
1) Huge page mapping of anonymous memory is initially invalid. Will be
faulted in by copy-on-write mechanism.
2) Userspace attempts store at the end of the huge mapping.
3) TLB Refill exception handler fill TLB with a normal (4K sized)
invalid page at the end of the huge mapping virtual address range.
4) Userspace restarted, and re-attempts the store at the end of the
huge mapping.
5) Page from #3 is invalid, we get a fault and go to the hugepage
fault handler. This tries to map a huge page and calls
huge_ptep_set_access_flags() to install the mapping.
6) We just call the generic ptep_set_access_flags() to set up the page
tables, but the flush there assumes a normal (4K sized) page and
only tries to flush the first part of the huge page virtual address
out of the TLB, since the existing entry from step #3 doesn't
conflict, nothing is flushed.
7) We attempt to load the mapping into the TLB, but because it
conflicts with the entry from step #3, we get a Machine Check
exception.
The fix: Flush the entire rage covered by the huge page in
huge_ptep_set_access_flags(), and remove the optimization in
local_flush_tlb_range() so that the flush actually does the correct
thing.
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: Hillf Danton <dhillf@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/4661/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
(cherry picked from commit dd617f258cc39d36be26afee9912624a2d23112c)
diff --git a/arch/mips/include/asm/hugetlb.h b/arch/mips/include/asm/hugetlb.h
index bd94946..ef99db9 100644
--- a/arch/mips/include/asm/hugetlb.h
+++ b/arch/mips/include/asm/hugetlb.h
@@ -95,7 +95,17 @@
pte_t *ptep, pte_t pte,
int dirty)
{
- return ptep_set_access_flags(vma, addr, ptep, pte, dirty);
+ int changed = !pte_same(*ptep, pte);
+
+ if (changed) {
+ set_pte_at(vma->vm_mm, addr, ptep, pte);
+ /*
+ * There could be some standard sized pages in there,
+ * get them all.
+ */
+ flush_tlb_range(vma, addr, addr + HPAGE_SIZE);
+ }
+ return changed;
}
static inline pte_t huge_ptep_get(pte_t *ptep)
diff --git a/arch/mips/mm/tlb-r4k.c b/arch/mips/mm/tlb-r4k.c
index 4b9b935..88e79ad 100644
--- a/arch/mips/mm/tlb-r4k.c
+++ b/arch/mips/mm/tlb-r4k.c
@@ -120,18 +120,11 @@
if (cpu_context(cpu, mm) != 0) {
unsigned long size, flags;
- int huge = is_vm_hugetlb_page(vma);
ENTER_CRITICAL(flags);
- if (huge) {
- start = round_down(start, HPAGE_SIZE);
- end = round_up(end, HPAGE_SIZE);
- size = (end - start) >> HPAGE_SHIFT;
- } else {
- start = round_down(start, PAGE_SIZE << 1);
- end = round_up(end, PAGE_SIZE << 1);
- size = (end - start) >> (PAGE_SHIFT + 1);
- }
+ start = round_down(start, PAGE_SIZE << 1);
+ end = round_up(end, PAGE_SIZE << 1);
+ size = (end - start) >> (PAGE_SHIFT + 1);
if (size <= current_cpu_data.tlbsize/2) {
int oldpid = read_c0_entryhi();
int newpid = cpu_asid(cpu, mm);
@@ -140,10 +133,7 @@
int idx;
write_c0_entryhi(start | newpid);
- if (huge)
- start += HPAGE_SIZE;
- else
- start += (PAGE_SIZE << 1);
+ start += (PAGE_SIZE << 1);
mtc0_tlbw_hazard();
tlb_probe();
tlb_probe_hazard();