RE: [PATCH] mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings of poison pages

["Elliott, Robert (Persistent Memory)" <elliott@hpe.com>]

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> owner@vger.kernel.org] On Behalf Of Luck, Tony
> Sent: Wednesday, June 21, 2017 12:54 PM
> To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Borislav Petkov <bp@suse.de>; Dave Hansen <dave.hansen@intel.com>;
> x86@kernel.org; linux-mm@kvack.org; linux-kernel@vger.kernel.org

(adding linux-nvdimm list in this reply)

> Subject: Re: [PATCH] mm/hwpoison: Clear PRESENT bit for kernel 1:1
> mappings of poison pages
> 
> On Wed, Jun 21, 2017 at 02:12:27AM +0000, Naoya Horiguchi wrote:
> 
> > We had better have a reverse operation of this to cancel the unmapping
> > when unpoisoning?
> 
> When we have unpoisoning, we can add something.  We don't seem to have
> an inverse function for "set_memory_np" to just flip the _PRESENT bit
> back on again. But it would be trivial to write a set_memory_pp().
> 
> Since we'd be doing this after the poison has been cleared, we wouldn't
> need to play games with the address.  We'd just use:
> 
> 	set_memory_pp((unsigned long)pfn_to_kaddr(pfn), 1);
> 
> -Tony

Persistent memory does have unpoisoning and would require this inverse
operation - see drivers/nvdimm/pmem.c pmem_clear_poison() and core.c
nvdimm_clear_poison().

---
Robert Elliott, HPE Persistent Memory