On 23/03/2022 16:21, Catalin Marinas wrote:
On Wed, Mar 23, 2022 at 11:51:25AM +0000, Steve Capper wrote:
On 22/03/2022 17:56, Catalin Marinas wrote:
At a quick look, we wouldn't have a problem with missing TLB flushing
since huge_ptep_get_and_clear() does this for contiguous PTEs. Not sure
why it needs this though, Steve added it in commit d8bdcff28764. I think
we can defer this flushing to tlb_remove_page_size().
The TLB flush in huge_ptep_get_and_clear() was added because it was called
by hugetlb_change_protection() without any flushing. The concern was that,
without the flush, it would be possible to get to different views of the
same contiguous huge page. (Being contiguous they were not changed en masse
atomically).
Maybe the code paths have been changed since but looking at
hugetlb_change_protection(), we have huge_ptep_modify_prot_start()
calling huge_ptep_get_and_clear() which AFAICT only needs to clear the
ptes. huge_ptep_modify_prot_commit() calls set_huge_pte_at() which does
another pte clearing + TLBI (clear_flush()) before setting the new ptes.
So we do the pte clearing and TLBI twice already.
Thanks, yeah indeed the code has changed and the flush should be removed
from the arm64 huge_ptep_get_and_clear.
Cheers,
--
Steve
