On 5/9/19 3:54 AM, Peter Zijlstra wrote:
On Thu, May 09, 2019 at 12:38:13PM +0200, Peter Zijlstra wrote:
That's tlb->cleared_p*, and yes agreed. That is, right until some
architecture has level dependent TLBI instructions, at which point we'll
need to have them all set instead of cleared.
Anyway; am I correct in understanding that the actual problem is that
we've cleared freed_tables and the ARM64 tlb_flush() will then not
invalidate the cache and badness happens?
Because so far nobody has actually provided a coherent description of
the actual problem we're trying to solve. But I'm thinking something
like the below ought to do.
There's another 'fun' issue I think. For architectures like ARM that
have range invalidation and care about VM_EXEC for I$ invalidation, the
below doesn't quite work right either.
I suspect we also have to force: tlb->vma_exec = 1.
Isn't the below code in tlb_flush enough to guarantee this?
...
} else if (tlb->end) {
struct vm_area_struct vma = {
.vm_mm = tlb->mm,
.vm_flags = (tlb->vma_exec ? VM_EXEC : 0) |
(tlb->vma_huge ? VM_HUGETLB : 0),
};
...
And I don't think there's an architecture that cares, but depending on
details I can construct cases where any setting of tlb->vm_hugetlb is
wrong, so that is _awesome_. But I suspect the sane thing for now is to
force it 0.
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
index 99740e1dd273..fe768f8d612e 100644
--- a/mm/mmu_gather.c
+++ b/mm/mmu_gather.c
@@ -244,15 +244,20 @@ void tlb_finish_mmu(struct mmu_gather *tlb,
unsigned long start, unsigned long end)
{
/*
- * If there are parallel threads are doing PTE changes on same range
- * under non-exclusive lock(e.g., mmap_sem read-side) but defer TLB
- * flush by batching, a thread has stable TLB entry can fail to flush
- * the TLB by observing pte_none|!pte_dirty, for example so flush TLB
- * forcefully if we detect parallel PTE batching threads.
+ * Sensible comment goes here..
*/
- if (mm_tlb_flush_nested(tlb->mm)) {
- __tlb_reset_range(tlb);
- __tlb_adjust_range(tlb, start, end - start);
+ if (mm_tlb_flush_nested(tlb->mm) && !tlb->full_mm) {
+ /*
+ * Since we're can't tell what we actually should have
+ * flushed flush everything in the given range.
+ */
+ tlb->start = start;
+ tlb->end = end;
+ tlb->freed_tables = 1;
+ tlb->cleared_ptes = 1;
+ tlb->cleared_pmds = 1;
+ tlb->cleared_puds = 1;
+ tlb->cleared_p4ds = 1;
}
tlb_flush_mmu(tlb);
