linux/drivers/lguest
Rusty Russell 4357bd9453 lguest: Revert 1ce70c4fac, fix real problem.
Ahmed managed to crash the Host in release_pgd(), which cannot be a Guest
bug, and indeed it wasn't.

The bug was that handing a 0 as the address of the toplevel page table
being manipulated can cause the lookup code in find_pgdir() to return
an uninitialized cache entry (we shadow up to 4 top level page tables
for each Guest).

Commit 37cc8d7f96 introduced this
behaviour in the Guest, uncovering the bug.

The patch which he submitted (which removed the /4 from the index
calculation) simply ensured that these high-indexed entries hit the
early exit path of guest_set_pmd().  But you get lots of segfaults in
guest userspace as the PMDs aren't being updated.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2008-03-11 09:35:58 +11:00
..
x86 lguest: fix mis-merge against hpa's TSS renaming 2008-01-31 19:59:44 +11:00
core.c lguest: fix __get_vm_area usage. 2008-03-11 09:35:56 +11:00
hypercalls.c lguest: Use explicit includes rateher than indirect 2008-01-30 22:50:19 +11:00
interrupts_and_traps.c lguest: get rid of lg variable assignments 2008-01-30 22:50:18 +11:00
Kconfig Remove bogus duplicate CONFIG_LGUEST_GUEST entry. 2008-01-19 21:29:39 -08:00
lg.h lguest: Use explicit includes rateher than indirect 2008-01-30 22:50:19 +11:00
lguest_device.c Fix container_of() usage 2008-02-08 09:22:32 -08:00
lguest_user.c lguest: make sure cpu is initialized before accessing it 2008-03-11 09:35:56 +11:00
Makefile Lguest support for Virtio 2007-10-23 15:49:56 +10:00
page_tables.c lguest: Revert 1ce70c4fac, fix real problem. 2008-03-11 09:35:58 +11:00
README lguest: documentation I: Preparation 2007-07-26 11:35:16 -07:00
segments.c lguest: get rid of lg variable assignments 2008-01-30 22:50:18 +11:00

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.