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 20:19:34 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Elliott, Robert (Persistent Memory)" <elliott@....com>,
        Borislav Petkov <bp@...e.de>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.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>,
        Yazen Ghannam <yazen.ghannam@....com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Kani, Toshimitsu" <toshi.kani@....com>,
        "Vaden, Tom (HPE Server OS Architecture)" <tom.vaden@....com>
Subject: RE: [PATCH] mm/hwpoison: Clear PRESENT bit for kernel 1:1 mappings
 of poison pages

>> +if (set_memory_np(decoy_addr, 1))
>> +pr_warn("Could not invalidate pfn=0x%lx from 1:1 map \n", pfn);
>
> Does this patch handle breaking up 512 GiB, 1 GiB or 2 MiB page mappings
> if it's just trying to mark a 4 KiB page as bad?

Yes.  The 1:1 mappings start out using the largest supported page size.  This
call will break up huge/large pages so that only 4KB is mapped out.
[This will affect performance because of the extra levels of TLB walks]

> Although the kernel doesn't use MTRRs itself anymore, what if the system
> BIOS still uses them for some memory regions, and the bad address falls in
> an MTRR region?

This code is called after mm/memory-failure.c:memory_failure() has already
checked that the page is one managed by the kernel.  In general machine checks
from other regions are going to be called out as fatal before we get here.

-Tony