Messages in this thread | | | Date | Wed, 22 Feb 2023 10:20:48 +0100 | From | Peter Zijlstra <> | Subject | Re: Official documentation from Intel stating that poking INT3 (single-byte) concurrently is OK ? |
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On Tue, Feb 21, 2023 at 01:42:58PM -0500, Mathieu Desnoyers wrote: > On 2023-02-21 12:50, Steven Rostedt wrote: > > On Tue, 21 Feb 2023 11:44:42 -0500 > > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > > > > > Hi Peter, > > > > > > I have emails from you dating from a few years back unofficially stating > > > that it's OK to update the first byte of an instruction with a single-byte > > > int3 concurrently: > > > > > > https://lkml.indiana.edu/hypermail/linux/kernel/1001.1/01530.html > > > > > > It is referred in the original implementation of text_poke_bp(): > > > commit fd4363fff3d9 ("x86: Introduce int3 (breakpoint)-based instruction patching") > > > > > > Olivier Dion is working on the libpatch [1,2] project aiming to use this > > > property for low-latency/low-overhead live code patching in user-space as > > > well, but we cannot find an official statement from Intel that guarantees > > > this breakpoint-bypass technique is indeed OK without stopping the world > > > while patching. > > > > > > Do you know where I could find an official statement of this guarantee ? > > > > > > > The fact that we have been using it for over 10 years without issue should > > be a good guarantee ;-) > > > > I know you probably prefer an official statement, and I thought they > > actually gave one, but can't seem to find it. > > I recall an in-person discussion with Peter Anvin shortly after he got the > official confirmation, but I cannot find any public trace of it. I suspect > Intel may have documented this internally only.
My 2ct, ISTR this also having been vetted by AMD, perhaps they did manage to write it down somewhere.
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