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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)
This commit is contained in:
David Daney 2012-12-03 12:44:26 -08:00 committed by Ralf Baechle
parent 9489e9dcae
commit ac53c4fca4
2 changed files with 15 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/mips/include/asm/hugetlb.h
View File

@ -95,7 +95,17 @@ static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
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)

10
arch/mips/mm/tlb-r4k.c
View File

@ -120,18 +120,11 @@ void local_flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
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);
}
if (size <= current_cpu_data.tlbsize/2) {
int oldpid = read_c0_entryhi();
int newpid = cpu_asid(cpu, mm);
@ -140,9 +133,6 @@ void local_flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
int idx;
write_c0_entryhi(start | newpid);
if (huge)
start += HPAGE_SIZE;
else
start += (PAGE_SIZE << 1);
mtc0_tlbw_hazard();
tlb_probe();