| Message ID | 20230810093241.1181142-1-qi.zheng@linux.dev (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: mm: use ptep_clear() instead of pte_clear() in clear_flush() | expand |
I wrote wrong Kefeng's email address before, correct it now. On 2023/8/10 17:32, Qi Zheng wrote: > From: Qi Zheng <zhengqi.arch@bytedance.com> > > In clear_flush(), the original pte may be a present entry, so we should > use ptep_clear() to let page_table_check track the pte clearing operation, > otherwise it may cause false positive in subsequent set_pte_at(). > > Fixes: 42b2547137f5 ("arm64/mm: enable ARCH_SUPPORTS_PAGE_TABLE_CHECK") > Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com> > --- > arch/arm64/mm/hugetlbpage.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c > index 21716c940682..9c52718ea750 100644 > --- a/arch/arm64/mm/hugetlbpage.c > +++ b/arch/arm64/mm/hugetlbpage.c > @@ -236,7 +236,7 @@ static void clear_flush(struct mm_struct *mm, > unsigned long i, saddr = addr; > > for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) > - pte_clear(mm, addr, ptep); > + ptep_clear(mm, addr, ptep); > > flush_tlb_range(&vma, saddr, addr); > }
On Thu, Aug 10, 2023 at 09:32:41AM +0000, Qi Zheng wrote: > From: Qi Zheng <zhengqi.arch@bytedance.com> > > In clear_flush(), the original pte may be a present entry, so we should > use ptep_clear() to let page_table_check track the pte clearing operation, > otherwise it may cause false positive in subsequent set_pte_at(). Isn't this true for most users of pte_clear()? There are some in the core code, so could they trigger the false positive as well? Will
On Fri, Aug 11, 2023 at 07:16:20PM +0800, Qi Zheng wrote: > Will Deacon <[1]will@kernel.org>于2023年8月11日 周五19:03写道： > > On Thu, Aug 10, 2023 at 09:32:41AM +0000, Qi Zheng wrote: > > From: Qi Zheng <[2]zhengqi.arch@bytedance.com> > > > > In clear_flush(), the original pte may be a present entry, so we > should > > use ptep_clear() to let page_table_check track the pte clearing > operation, > > otherwise it may cause false positive in subsequent set_pte_at(). > > Isn't this true for most users of pte_clear()? There are some in the > core > code, so could they trigger the false positive as well? > > No, the PTE entry in other places where pte_clear() is used is non-present > PTE. > The page_table_check does not does track the pte operation in this case, > so it will not cause false positives. Are you sure? For example, the call from flush_all_zero_pkmaps() in highmem.c really looks like it's clearing a valid entry. Not that arm64 cares about highmem, but still. Will
On Fri, 11 Aug 2023 19:28:41 +0800 Qi Zheng <zhengqi.arch@bytedance.com> wrote: > Will Deacon <will@kernel.org>于2023年8月11日 周五19:21写道： > > > On Fri, Aug 11, 2023 at 07:16:20PM +0800, Qi Zheng wrote: > > > Will Deacon <[1]will@kernel.org>于2023年8月11日 周五19:03写道： > > > > > > On Thu, Aug 10, 2023 at 09:32:41AM +0000, Qi Zheng wrote: > > > > From: Qi Zheng <[2]zhengqi.arch@bytedance.com> > > > > > > > > In clear_flush(), the original pte may be a present entry, so we > > > should > > > > use ptep_clear() to let page_table_check track the pte clearing > > > operation, > > > > otherwise it may cause false positive in subsequent set_pte_at(). > > > > > > Isn't this true for most users of pte_clear()? There are some in the > > > core > > > code, so could they trigger the false positive as well? > > > > > > No, the PTE entry in other places where pte_clear() is used is > > non-present > > > PTE. > > > The page_table_check does not does track the pte operation in this > > case, > > > so it will not cause false positives. > > > > Are you sure? For example, the call from flush_all_zero_pkmaps() in > > highmem.c really looks like it's clearing a valid entry. Not that arm64 > > cares about highmem, but still. > > > Ah, this is init_mm, not user mm, page_table_check does not care about this > case. It's unclear where we stand with this patch. An ack or a nack, please?
On 2023/8/22 04:21, Andrew Morton wrote: > On Fri, 11 Aug 2023 19:28:41 +0800 Qi Zheng <zhengqi.arch@bytedance.com> wrote: > >> Will Deacon <will@kernel.org>于2023年8月11日 周五19:21写道： >> >>> On Fri, Aug 11, 2023 at 07:16:20PM +0800, Qi Zheng wrote: >>>> Will Deacon <[1]will@kernel.org>于2023年8月11日 周五19:03写道： >>>> >>>> On Thu, Aug 10, 2023 at 09:32:41AM +0000, Qi Zheng wrote: >>>> > From: Qi Zheng <[2]zhengqi.arch@bytedance.com> >>>> > >>>> > In clear_flush(), the original pte may be a present entry, so we >>>> should >>>> > use ptep_clear() to let page_table_check track the pte clearing >>>> operation, >>>> > otherwise it may cause false positive in subsequent set_pte_at(). >>>> >>>> Isn't this true for most users of pte_clear()? There are some in the >>>> core >>>> code, so could they trigger the false positive as well? >>>> >>>> No, the PTE entry in other places where pte_clear() is used is >>> non-present >>>> PTE. >>>> The page_table_check does not does track the pte operation in this >>> case, >>>> so it will not cause false positives. >>> >>> Are you sure? For example, the call from flush_all_zero_pkmaps() in >>> highmem.c really looks like it's clearing a valid entry. Not that arm64 >>> cares about highmem, but still. >> >> >> Ah, this is init_mm, not user mm, page_table_check does not care about this >> case. > > It's unclear where we stand with this patch. An ack or a nack, please? Hi all, Any comments or suggestions here? Thanks, Qi
On Mon, Aug 21, 2023 at 01:21:19PM -0700, Andrew Morton wrote: > On Fri, 11 Aug 2023 19:28:41 +0800 Qi Zheng <zhengqi.arch@bytedance.com> wrote: > > > Will Deacon <will@kernel.org>于2023年8月11日 周五19:21写道： > > > > > On Fri, Aug 11, 2023 at 07:16:20PM +0800, Qi Zheng wrote: > > > > Will Deacon <[1]will@kernel.org>于2023年8月11日 周五19:03写道： > > > > > > > > On Thu, Aug 10, 2023 at 09:32:41AM +0000, Qi Zheng wrote: > > > > > From: Qi Zheng <[2]zhengqi.arch@bytedance.com> > > > > > > > > > > In clear_flush(), the original pte may be a present entry, so we > > > > should > > > > > use ptep_clear() to let page_table_check track the pte clearing > > > > operation, > > > > > otherwise it may cause false positive in subsequent set_pte_at(). > > > > > > > > Isn't this true for most users of pte_clear()? There are some in the > > > > core > > > > code, so could they trigger the false positive as well? > > > > > > > > No, the PTE entry in other places where pte_clear() is used is > > > non-present > > > > PTE. > > > > The page_table_check does not does track the pte operation in this > > > case, > > > > so it will not cause false positives. > > > > > > Are you sure? For example, the call from flush_all_zero_pkmaps() in > > > highmem.c really looks like it's clearing a valid entry. Not that arm64 > > > cares about highmem, but still. > > > > > > Ah, this is init_mm, not user mm, page_table_check does not care about this > > case. > > It's unclear where we stand with this patch. An ack or a nack, please? Sorry Andrew, I saw you'd queued it so I marked it as "done" on my list. I think it's fine: Acked-by: Will Deacon <will@kernel.org> Will
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index 21716c940682..9c52718ea750 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -236,7 +236,7 @@ static void clear_flush(struct mm_struct *mm, unsigned long i, saddr = addr; for (i = 0; i < ncontig; i++, addr += pgsize, ptep++) - pte_clear(mm, addr, ptep); + ptep_clear(mm, addr, ptep); flush_tlb_range(&vma, saddr, addr); }