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From: Pavel Machek <pavel@ucw.cz>
To: vbabka@suse.cz, mhocko@suse.com, hpa@zytor.com,
	torvalds@linux-foundation.org, ak@linux.intel.com,
	dave.hansen@intel.com, kernel list <linux-kernel@vger.kernel.org>,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de
Subject: l1tf: Kernel suggests I throw away third of my memory. I'd rather not
Date: Wed, 17 Oct 2018 12:56:10 +0200	[thread overview]
Message-ID: <20181017105610.GA4260@amd> (raw)

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Hi!

6a012288 suggests I throw away 1GB on RAM. On 3GB system.. that is not
going to be pleasant.

l1tf.html says:

# The Linux kernel contains a mitigation for this attack vector, PTE
# inversion, which is permanently enabled and has no performance
# impact.

I don't believe it has "no" performance impact, but I guess it is lost
in the noise.

#  The kernel ensures that the address bits of PTEs, which are
# not marked present, never point to cacheable physical memory space.

# A system with an up to date kernel is protected against attacks from
# malicious user space applications.

These are not true.

cat /sys/devices/system/cpu/vulnerabilities/l1tf
Vulnerable
uname -a
Linux amd 4.19.0-rc8-next-20181017autobisect1539371050 #189 SMP Wed
Oct 17 12:04:23 CEST 2018 i686 GNU/Linux

Now question is... can we do better? Kernel stores information about
swapped-out pages there, right? That sounds like a cool hack, but
maybe it is time to get rid of that hack?

As a workaround, can I simply do swapoff -a to be safe for now?

Thanks,
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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             reply	other threads:[~2018-10-17 10:56 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-17 10:56 Pavel Machek [this message]
2018-10-17 11:15 ` l1tf: Kernel suggests I throw away third of my memory. I'd rather not Michal Hocko
2018-10-17 11:32   ` Pavel Machek
2018-10-17 12:17     ` Michal Hocko
2018-10-17 22:21     ` Dave Hansen
2018-10-18  7:10       ` Vlastimil Babka
2018-10-17 14:08 ` Andi Kleen
2018-10-17 14:13   ` Vlastimil Babka

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