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From: Jason Gunthorpe <jgg@ziepe.ca>
To: "lizhijian@fujitsu.com" <lizhijian@fujitsu.com>
Cc: "nvdimm@lists.linux.dev" <nvdimm@lists.linux.dev>,
	Yishai Hadas <yishaih@nvidia.com>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"yangx.jy@fujitsu.com" <yangx.jy@fujitsu.com>
Subject: Re: RDMA/rpma + fsdax(ext4) was broken since 36f30e486d
Date: Fri, 27 Aug 2021 09:10:34 -0300	[thread overview]
Message-ID: <20210827121034.GG1200268@ziepe.ca> (raw)
In-Reply-To: <10c4bead-c778-8794-f916-80bf7ba3a56b@fujitsu.com>

On Fri, Aug 27, 2021 at 08:15:40AM +0000, lizhijian@fujitsu.com wrote:
> i looked over the change-log of hmm_vma_handle_pte(), and found that before
> 4055062 ("mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling")
> 
> hmm_vma_handle_pte() will not check pte_special(pte) if pte_devmap(pte) is true.
> 
> when we reached
> "if (pte_special(pte) && !is_zero_pfn(pte_pfn(pte))) {"
> the pte have already presented and its pte's flag already fulfilled the request flags.
> 
> 
> My question is that
> Per https://01.org/blogs/dave/2020/linux-consumption-x86-page-table-bits,
> pte_devmap(pte) and pte_special(pte) could be both true in fsdax user case, right ?

How? what code creates that?

I see:

insert_pfn():
	/* Ok, finally just insert the thing.. */
	if (pfn_t_devmap(pfn))
		entry = pte_mkdevmap(pfn_t_pte(pfn, prot));
	else
		entry = pte_mkspecial(pfn_t_pte(pfn, prot));

So what code path ends up setting both bits?

Jason

  reply	other threads:[~2021-08-27 12:10 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <8b2514bb-1d4b-48bb-a666-85e6804fbac0@cn.fujitsu.com>
2021-08-04  8:06 ` Li, Zhijian/李 智坚
2021-08-06  1:45   ` Jason Gunthorpe
2021-08-06  3:20     ` Li, Zhijian/李 智坚
2021-08-27  8:15       ` lizhijian
2021-08-27 12:10         ` Jason Gunthorpe [this message]
2021-08-27 13:05           ` Li, Zhijian
2021-08-27 13:16             ` Jason Gunthorpe
2021-08-27 13:38               ` Li, Zhijian
2021-08-27 16:42             ` Dan Williams
2021-08-27 16:52               ` Jason Gunthorpe

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