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f87e0434a3
In a798f091113e ("x86/entry/32: Change INT80 to be an interrupt gate")
Andy broke lguest. This is because lguest had special code to allow
the 0x80 trap gate go straight into the guest itself; interrupts gates
(without more work, as mentioned in the file's comments) bounce via
the hypervisor.
His change made them go via the hypervisor, but as it's in the range of
normal hardware interrupts, they were not directed through to the guest
at all. Turns out the guest userspace isn't very effective if syscalls
are all noops.
I haven't ripped out all the now-useless trap-direct-to-guest-kernel
code yet, since it will still be needed if someone decides to update
this optimization.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Weisbecker <fweisbec@gmail.com>
Cc: x86\@kernel.org
Link: http://lkml.kernel.org/r/87fuv685kl.fsf@rustcorp.com.au
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Welcome, friend reader, to lguest. Lguest is an adventure, with you, the reader, as Hero. I can't think of many 5000-line projects which offer both such capability and glimpses of future potential; it is an exciting time to be delving into the source! But be warned; this is an arduous journey of several hours or more! And as we know, all true Heroes are driven by a Noble Goal. Thus I offer a Beer (or equivalent) to anyone I meet who has completed this documentation. So get comfortable and keep your wits about you (both quick and humorous). Along your way to the Noble Goal, you will also gain masterly insight into lguest, and hypervisors and x86 virtualization in general. Our Quest is in seven parts: (best read with C highlighting turned on) I) Preparation - In which our potential hero is flown quickly over the landscape for a taste of its scope. Suitable for the armchair coders and other such persons of faint constitution. II) Guest - Where we encounter the first tantalising wisps of code, and come to understand the details of the life of a Guest kernel. III) Drivers - Whereby the Guest finds its voice and become useful, and our understanding of the Guest is completed. IV) Launcher - Where we trace back to the creation of the Guest, and thus begin our understanding of the Host. V) Host - Where we master the Host code, through a long and tortuous journey. Indeed, it is here that our hero is tested in the Bit of Despair. VI) Switcher - Where our understanding of the intertwined nature of Guests and Hosts is completed. VII) Mastery - Where our fully fledged hero grapples with the Great Question: "What next?" make Preparation! Rusty Russell.