From: Joerg Roedel <jroedel@suse.de>
To: Meelis Roos <mroos@linux.ee>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Linux Kernel list <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, Andrea Arcangeli <aarcange@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: 32-bit PTI with THP = userspace corruption
Date: Tue, 11 Sep 2018 14:12:22 +0200 [thread overview]
Message-ID: <20180911121128.ikwptix6e4slvpt2@suse.de> (raw)
In-Reply-To: <alpine.LRH.2.21.1809111454100.29433@math.ut.ee>
On Tue, Sep 11, 2018 at 02:58:10PM +0300, Meelis Roos wrote:
> The machines where I have PAE off are the ones that have less memory.
> PAE is off just for performance reasons, not lack of PAE. PAE should be
> present on all of my affected machines anyway and current distributions
> seem to mostly assume 686 and PAE anyway for 32-bit systems.
Right, most distributions don't even provide a non-PAE kernel for their
users anymore.
How big is the performance impact of using PAE over legacy paging? It
shouldn't be too big because the top-level of the page-table only has 4
entries and is completly cached in the CPU. This makes %cr3 switches
slower, but the page-walk itself still only needs 2 memory accesses.
The page-table entries are also 8 bytes instead of 4 bytes, so that
there is less locality in page-walks and probably a higher cache-miss
rate.
Regards,
Joerg
next prev parent reply other threads:[~2018-09-11 12:12 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-30 18:09 32-bit PTI with THP = userspace corruption Meelis Roos
2018-08-30 20:55 ` Joerg Roedel
2018-08-31 4:12 ` Meelis Roos
2018-08-31 7:07 ` Joerg Roedel
2018-09-08 10:24 ` Thomas Gleixner
2018-09-11 11:49 ` Joerg Roedel
2018-09-11 11:58 ` Meelis Roos
2018-09-11 12:12 ` Joerg Roedel [this message]
2018-09-18 13:00 ` Alan Cox
2018-10-21 12:37 ` Pavel Machek
2018-10-22 7:56 ` Joerg Roedel
2018-10-22 18:48 ` Alan Cox
2018-10-23 9:11 ` Not-so-old machines without PAE was " Pavel Machek
2018-10-22 20:56 ` Pavel Machek
2018-09-11 18:20 ` Linus Torvalds
2018-08-31 7:10 ` Meelis Roos
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