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From: Dan Williams <dan.j.williams@intel.com>
Date: Mon, 4 Jun 2018 10:39:48 -0700
Message-ID: <CAPcyv4g76nv=D2NXrpFLS-aWQR=N0T2n01WhrVY2_KPavkvLCA@mail.gmail.com>
Subject: Re: [PATCH v2 07/11] x86, memory_failure: Introduce {set, clear}_mce_nospec()
To: "Luck, Tony" <tony.luck@intel.com>
Cc: linux-nvdimm <linux-nvdimm@lists.01.org>, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
	linux-edac@vger.kernel.org, X86 ML <x86@kernel.org>, Christoph Hellwig <hch@lst.de>,
	Linux MM <linux-mm@kvack.org>, linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Jan Kara <jack@suse.cz>
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On Mon, Jun 4, 2018 at 10:08 AM, Luck, Tony <tony.luck@intel.com> wrote:
> On Sat, Jun 02, 2018 at 10:23:20PM -0700, Dan Williams wrote:
>> +static inline int set_mce_nospec(unsigned long pfn)
>> +{
>> +     int rc;
>> +
>> +     rc = set_memory_uc((unsigned long) __va(PFN_PHYS(pfn)), 1);
>
> You should really do the decoy_addr thing here that I had in mce_unmap_kpfn().
> Putting the virtual address of the page you mustn't accidentally prefetch
> from into a register is a pretty good way to make sure that the processor
> does do a prefetch.

Maybe I'm misreading, but doesn't that make the page completely
inaccessible? We still want to read pmem through the driver and the
linear mapping with memcpy_mcsafe(). Alternatively I could just drop
this patch and setup a private / alias mapping for the pmem driver to
use. It seems aliased mappings would be the safer option, but I want
to make sure I've comprehended your suggestion correctly?