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* [PATCH v3] mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled
@ 2021-08-30  9:42 Li Zhijian
  2021-08-30 10:09 ` Christoph Hellwig
  2021-08-30 12:40 ` Jason Gunthorpe
  0 siblings, 2 replies; 3+ messages in thread
From: Li Zhijian @ 2021-08-30  9:42 UTC (permalink / raw)
  To: linux-mm, linux-rdma, akpm, jglisse, jgg, hch
  Cc: yishaih, linux-kernel, Li Zhijian, stable

Previously, we noticed the one rpma example was failed[1] since 36f30e486d,
where it will use ODP feature to do RDMA WRITE between fsdax files.

After digging into the code, we found hmm_vma_handle_pte() will still
return EFAULT even though all the its requesting flags has been
fulfilled. That's because a DAX page will be marked as
(_PAGE_SPECIAL | PAGE_DEVMAP) by pte_mkdevmap().

[1]: https://github.com/pmem/rpma/issues/1142

CC: stable@vger.kernel.org
Fixes: 405506274922 ("mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling")
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>

---
V3: adjust the checking order
---
 mm/hmm.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index fad6be2bf072..842e26599238 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -295,10 +295,13 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
 		goto fault;
 
 	/*
+	 * Bypass devmap pte such as DAX page when all pfn requested
+	 * flags(pfn_req_flags) are fulfilled.
 	 * Since each architecture defines a struct page for the zero page, just
 	 * fall through and treat it like a normal page.
 	 */
-	if (pte_special(pte) && !is_zero_pfn(pte_pfn(pte))) {
+	if (pte_special(pte) && !pte_devmap(pte) &&
+	    !is_zero_pfn(pte_pfn(pte))) {
 		if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {
 			pte_unmap(ptep);
 			return -EFAULT;
-- 
2.31.1




^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v3] mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled
  2021-08-30  9:42 [PATCH v3] mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled Li Zhijian
@ 2021-08-30 10:09 ` Christoph Hellwig
  2021-08-30 12:40 ` Jason Gunthorpe
  1 sibling, 0 replies; 3+ messages in thread
From: Christoph Hellwig @ 2021-08-30 10:09 UTC (permalink / raw)
  To: Li Zhijian
  Cc: linux-mm, linux-rdma, akpm, jglisse, jgg, hch, yishaih,
	linux-kernel, stable

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH v3] mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled
  2021-08-30  9:42 [PATCH v3] mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled Li Zhijian
  2021-08-30 10:09 ` Christoph Hellwig
@ 2021-08-30 12:40 ` Jason Gunthorpe
  1 sibling, 0 replies; 3+ messages in thread
From: Jason Gunthorpe @ 2021-08-30 12:40 UTC (permalink / raw)
  To: Li Zhijian, akpm
  Cc: linux-mm, linux-rdma, jglisse, hch, yishaih, linux-kernel, stable

On Mon, Aug 30, 2021 at 05:42:32PM +0800, Li Zhijian wrote:
> Previously, we noticed the one rpma example was failed[1] since 36f30e486d,
> where it will use ODP feature to do RDMA WRITE between fsdax files.
> 
> After digging into the code, we found hmm_vma_handle_pte() will still
> return EFAULT even though all the its requesting flags has been
> fulfilled. That's because a DAX page will be marked as
> (_PAGE_SPECIAL | PAGE_DEVMAP) by pte_mkdevmap().
> 
> [1]: https://github.com/pmem/rpma/issues/1142
> 
> CC: stable@vger.kernel.org
> Fixes: 405506274922 ("mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling")
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> 
> ---
> V3: adjust the checking order
> ---
>  mm/hmm.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Andrew, can you grab this please?

Thanks,
Jason

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2021-08-30 12:40 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-08-30  9:42 [PATCH v3] mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled Li Zhijian
2021-08-30 10:09 ` Christoph Hellwig
2021-08-30 12:40 ` Jason Gunthorpe

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