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

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Date:   Wed, 21 Jun 2017 10:54:03 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:     Borislav Petkov <bp@...e.de>, Dave Hansen <dave.hansen@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
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