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Date: Wed, 29 Jul 2020 08:36:33 +0000
From: David Laight <David.Laight@...LAB.COM>
To: "'Madhavan T. Venkataraman'" <madvenka@...ux.microsoft.com>, "Andy
Lutomirski" <luto@...nel.org>
CC: "kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>, "linux-api@...r.kernel.org"
<linux-api@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>, "linux-fsdevel@...r.kernel.org"
<linux-fsdevel@...r.kernel.org>, "linux-integrity@...r.kernel.org"
<linux-integrity@...r.kernel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "linux-security-module@...r.kernel.org"
<linux-security-module@...r.kernel.org>, "oleg@...hat.com" <oleg@...hat.com>,
"x86@...nel.org" <x86@...nel.org>
Subject: RE: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor
From: Madhavan T. Venkataraman
> Sent: 28 July 2020 19:52
...
> trampfd faults are instruction faults that go through a different code path than
> the one that calls handle_mm_fault(). Perhaps, it is the handle_mm_fault() that
> is time consuming. Could you clarify?
Given that the expectation is a few instructions in userspace
(eg to pick up the original arguments for a nested call)
the (probable) thousands of clocks taken by entering the
kernel (especially with page table separation) is a massive
delta.
If entering the kernel were cheap no one would have added
the DSO functions for getting the time of day.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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