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From: "Elliott, Robert (Persistent Memory)" <elliott@hpe.com>
Subject: RE: [PATCH] mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings of
 poison pages
Date: Fri, 23 Jun 2017 22:19:35 +0000
Message-ID: <AT5PR84MB00823EB30BD7BF0EA3DAFF0BABD80@AT5PR84MB0082.NAMPRD84.PROD.OUTLOOK.COM>
References: <20170616190200.6210-1-tony.luck@intel.com>
 <20170619180147.qolal6mz2wlrjbxk@pd.tnic>
 <20170621174740.npbtg2e4o65tyrss@intel.com>
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To: "Luck, Tony" <tony.luck@intel.com>, Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@intel.com>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, "x86@kernel.org" <x86@kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Yazen Ghannam <yazen.ghannam@amd.com>, "Kani,
 Toshimitsu" <toshi.kani@hpe.com>, "'dan.j.williams@intel.com'" <dan.j.williams@intel.com>, "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>

> > > +	if (set_memory_np(decoy_addr, 1))
> > > +		pr_warn("Could not invalidate pfn=3D0x%lx from 1:1 map \n",

Another concept to consider is mapping the page as UC rather than
completely unmapping it.

The uncorrectable error scope could be smaller than a page size, like:
* memory ECC width (e.g., 8 bytes)
* cache line size (e.g., 64 bytes)
* block device logical block size (e.g., 512 bytes, for persistent memory)

UC preserves the ability to access adjacent data within the page that
hasn't gone bad, and is particularly useful for persistent memory.

---
Robert Elliott, HPE Persistent Memory


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