SKAS mode not working, x86_64 SMP host, x86_64 guest, problems with noprocmm

Hello everybody,
I've been trying to get x86_64 guest UMLs working on SMP x86_64 host machine for quite long time, during today and yesterday I've also checked 2.6.18 (+ both skas & skas-fremap v9pre9), but it's still not working as good as 32bit/32bit was working for me for last few years ;). Soo, do You somebody know what could I be doing wrong? Running full SKAS kernel segfaults with following error:

Kernel panic - not syncing: map_stub_pages : /proc/mm map for code 

failed, err = 22
(full trace listing below)
I've noticed on some other discussions that SKAS mode is still not fully working on x86_64, so I'd like to ask, what are remaining issues, and maybe could I somehow try helping in fixing them? I wonder why /proc/mm is used, what's /proc/mm64? shouldn't it be used instead? Running noprocmm or skas0 mode is a bit better, guest system seems to be working quite OK (at least with 2.6.18, older kernels had some networking issues), but when I try to shutdown guest, it hangs at last stage, remaining uml process cycling:
--- SIGVTALRM (Virtual timer expired) @ 0 (0) --- rt_sigprocmask(SIG_UNBLOCK, [USR1], [USR1 ALRM VTALRM WINCH IO], 8) = 0 gettimeofday({1159632583, 625562}, NULL) = 0 gettimeofday({1159632583, 625582}, NULL) = 0 gettimeofday({1159632583, 625603}, NULL) = 0
rt_sigreturn(0x1) = 2266636588
forever, consuming all CPU time and waiting to be shot by 9mm signal.. Any ideas?
thanks in advance
NiK.

and promised SKAS mode segfault trace:

[42949373.810000] Kernel panic - not syncing: map_stub_pages : /proc/mm 
map for code failed, err = 22
[42949373.810000]
[42949373.810000]
[42949373.810000] Modules linked in:
[42949373.810000] Pid: 1, comm: swapper Not tainted 2.6.18lb2.00_01_PRE01
[42949373.810000] RIP: 0033:[<00000000601ceb99>]
[42949373.810000] RSP: 00002b07c6a7afd0  EFLAGS: 00000246
[42949373.810000] RAX: 0000000000000000 RBX: 0000000000002969 RCX: 
ffffffffffffffff
[42949373.810000] RDX: 0000000000000000 RSI: 0000000000000013 RDI: 
0000000000002969
[42949373.810000] RBP: 0000000000002966 R08: 0000000000000001 R09: 
0000000000000000
[42949373.810000] R10: 0000000000000000 R11: 0000000000000246 R12: 
00002b07c6a7a000
[42949373.810000] R13: 00007fffe402d328 R14: 00007fffe402d7b8 R15: 
00007fffe402d7e8
[42949373.810000] Call Trace:
[42949373.810000] 60ecb968:  [<60018d0a>] panic_exit+0x2a/0x50
[42949373.810000] 60ecb978:  [<6005dba0>] notifier_call_chain+0x20/0x40
[42949373.810000] 60ecb998:  [<60049bdf>] panic+0xcf/0x170
[42949373.810000] 60ecb9e0:  [<60014f40>] copy_to_user_proc+0x0/0x30
[42949373.810000] 60ecb9f8:  [<600838e6>] prep_new_page+0x126/0x200
[42949373.810000] 60ecba18:  [<601fa139>] __syscall_error_1+0x6/0x1d
[42949373.810000] 60ecba28:  [<60038ba5>] file_io+0x35/0x110
[42949373.810000] 60ecba38:  [<60014f40>] copy_to_user_proc+0x0/0x30
[42949373.810000] 60ecba78:  [<6003f83a>] map_stub_pages+0x13a/0x280
[42949373.810000] 60ecbac8:  [<60084079>] __alloc_pages+0x59/0x2e0
[42949373.810000] 60ecbb78:  [<6001c5d1>] new_mm+0x61/0x80
[42949373.810000] 60ecbb98:  [<6001bfd7>] init_new_context_skas+0x117/0x1e0
[42949373.810000] 60ecbba8:  [<60013b67>] pgd_alloc+0x67/0x70
[42949373.810000] 60ecbbe8:  [<600ad808>] do_execve+0x278/0x290
[42949373.810000] 60ecbc10:  [<600121b0>] init+0x0/0x170
[42949373.810000] 60ecbc38:  [<60012a74>] execve1+0x24/0x80
[42949373.810000] 60ecbc68:  [<60012ada>] um_execve+0xa/0x50
[42949373.810000] 60ecbc78:  [<600b53f9>] dupfd+0x79/0xb0
[42949373.810000] 60ecbc88:  [<60012179>] run_init_process+0x49/0x80
[42949373.810000] 60ecbc98:  [<600121b0>] init+0x0/0x170
[42949373.810000] 60ecbcb8:  [<6001227f>] init+0xcf/0x170
[42949373.810000] 60ecbcd8:  [<6003aeee>] run_kernel_thread+0x4e/0x60
[42949373.810000] 60ecbcf8:  [<600121b0>] init+0x0/0x170
[42949373.810000] 60ecbd08:  [<600121b0>] init+0x0/0x170
[42949373.810000] 60ecbd38:  [<6003aecb>] run_kernel_thread+0x2b/0x60
[42949373.810000] 60ecbd88:  [<60044e52>] schedule_tail+0x32/0x1b0
[42949373.810000] 60ecbdd8:  [<6001c2ed>] new_thread_handler+0xdd/0x140
[42949373.810000] 60ecbe38:  [<601ce6b0>] __restore_rt+0x0/0x10
[42949373.810000] 60ecbee8:  [<601ceb99>] __kill+0x9/0x20

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skas0 works fine (as well as on i386) afaik.

Putting a stock kernel on the host or "noprocmm" on the UML command line will put you in skas0 mode.

Well, the -EINVAL return from writing /proc/mm would be a good place to start looking to fix things :-)

Jeff

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Hi Jeff,
thanks for reply!
yup, skas0 seems to be working quite OK, but do You have an idea where could be problem with shutting down? (this Virtual timer expired cycling?) and regarding /proc/mm, shouldn't this mm64 file be used? or what's it used for?
nik

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Oops, missed that in your previous message.

Where in the shutdown process is this? There have been some previous reports of hangs during swapoff which I have been unable to reproduce. I spent part of a day last week pushing UMLs deeply into swap and shutting them down, always successfully.

The SIGVTALRM is normal - that's just the timer. That strace you sent looks like the idle loop, so as far as the kernel is concerned, everything is fine.

/proc/mm64? What would it do that /proc/mm doesn't?

Jeff

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it always hangs executing /sbin/halt

it's consuming all available host CPU time, it's certainly cycling as fast as possible

well, I must admit I don't know what's difference between two at all, I was just guessing. Is there some documentation about it? I wasn't able to find nothing which would explain it...

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hmm, I've also noticed another strange thing (maybe bug?) when I run this UML using noprocmm, arch is incorrectly reported as i686, while if I run it using skas0, it's (correctly) reported as x86_64...
n.
PS: You don't need to CC me, I'm reading this list

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oops, so difference is not in mode, problems seems to be in NPTL usage, arch is correctly reported only when I set LD_ASSUME_KERNEL to 2.4.1 sorry about confusion...

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Jeff,
I'm terribly sorry, please ignore previous two emails. Problem was not in UML itself, but in my scripts, as it happened that I was running it with setarch i386, which caused guest uml report i386 architecture, and it made quite a mess when I was testing it...
once again I'm sorry, I guess I really should rather have some sleep :( n.
PS: but anyways, I wonder, is this behavior bug or feature? that running x86_64 uml using setarch i386 then causes guest UML report i686 arch? (even it's still x86_64)

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It is a bug. Under setarch i386, uname returns i686; however, UML should correct this. A 32bit UML says i686 on a 64bit host. Patch attached (compile-tested).
Please report whether it works or not.

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade

Index: linux-2.6.git/arch/um/os-Linux/util.c
===================================================================
@@ -81,11 +81,18 @@ void setup_machinename(char *machine_out
 	struct utsname host;
 
 	uname(&host);
-#if defined(UML_CONFIG_UML_X86) && !defined(UML_CONFIG_64BIT)
+#ifdef UML_CONFIG_UML_X86
+# ifndef UML_CONFIG_64BIT
 	if (!strcmp(host.machine, "x86_64")) {
 		strcpy(machine_out, "i686");
 		return;
 	}
+# else
+	if (!strcmp(host.machine, "i686")) {
+		strcpy(machine_out, "x86_64");
+		return;
+	}
+# endif
 #endif
 	strcpy(machine_out, host.machine);
 }

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Well, I'll explain everything (even to Jeff, since I never documented anything of this).

The SKAS patch V8 supports well i386 host and i386 guest. That's all. SKAS patch V9-preX tries to support x86_64 host, with both 32 and 64 bit guests:

* 32 bit guests: a bug prevents using full SKAS3, you must pass noprocmm and you'll get most performance advantages (because faultinfo works). When I worked on the SKAS port to x86_64 I did not discover that something worked, and I never tested support for 64bit guests.
I latter discovered the bug is in a different portion of code - Bodo Stroesser unveiled it, and I think this is the same bug that hit even Jeff's 1st attempt to write SKAS4 (all I know can be found in
http://user-mode-linux.sourceforge.net/diary.html -> grep skas4 and you'll find what I'm talking about on 23 Sep 2004).

* 64bit guests: they do not support SKAS3, but the host patch gives the needed support - to do that, the 1st thing to do would be to use /proc/mm64 as you point out (and it could even suffice, even if I doubt that), but guest kernels still try to use /proc/mm and it does not work. So you must pass skas0 on the cmdline (I do not remember whether noprocmm works for this case).

-EINVAL is given on purpose: the request struct UML writes on /proc/mm has a different layout for 32 and 64bit requests, or better a different size since pointers are larger (and there's an explicit check for that - IIRC it has always been there). I chose to have a separate /proc/mm64, I did not think to try autodetection. And frankly my first impression is that I'd still do it this way.

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
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Hi Paolo and others,
thanks a lot for explanation. I'll just add some things I've noticed (and also few another questions ;):
My setup is dualcore opteron machine, running SMP 2.6.18, patched with skasv9-pre9 with fremap support.
guests:
vanilla 2.6.18-x86_64 SKAS
- crashes trying to access /proc/mm
vanilla 2.6.18-x86_64 noprocmm OR skas0
- works equally well, even performance is pretty much the same
(measured on kernel compilation), there's just this problem with /sbin/halt hang
vanilla 2.6.18-x86 - doesn't matter which arguments are passed
- hangs, strace shows following:
old_mmap(NULL, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xfffffffff7f40000

        mmap2(NULL, 4096, PROT_READ|PROT_WRITE|PROT_EXEC, 
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xfffffffff7f3f000
        clone(child_stack=0xf7f3ffd4, flags=|SIGCHLD) = 8120
        waitpid(8120, [{WIFSIGNALED(s) && WTERMSIG(s) == SIGKILL}], 

WSTOPPED) = 8120
--- SIGCHLD (Child exited) @ 0 (0) ---
and child process dies this way:
getppid() = 8119
rt_sigprocmask(SIG_BLOCK, [WINCH], [], 8) = 0
ptrace(PTRACE_TRACEME, 0, 0, 0) = -1 EPERM (Operation
not permitted)
dup(2) = 4
fcntl64(4, F_GETFL) = 0x8002 (flags
O_RDWR|O_LARGEFILE)

        fstat64(0x4, 0xf7f3fa44)                = 0
        old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, 

MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xfffffffff7f3e000
_llseek(4, 0, 0xf7f3faa4, SEEK_CUR) = -1 ESPIPE (Illegal seek)
write(4, "ptrace: Operation not permitted\n", 32) = 32
close(4) = 0
munmap(0xf7f3e000, 4096) = 0
kill(8120, SIGKILL) = 0
+++ killed by SIGKILL +++

2.6.18-x86_64 with bb1 patch
- SKAS crashes as expected
- noprocmm or skas0 is weird:
if run, panics with:
[42949373.500000] VFS: Mounted root (ext2 filesystem) readonly.
Usage: init 0123456SsQqAaBbCcUu
[42949373.500000] Kernel panic - not syncing: Attempted to
kill init!
- aparentrly init is being executed in some strange way?
- given init=/bin/sh hangs, tracing shows following loop:
--- SIGCHLD (Child exited) @ 0 (0) ---
wait4(1381, [{WIFSTOPPED(s) && WSTOPSIG(s) == SIGSEGV}],
WSTOPPED, NULL) = 1381

        ptrace(PTRACE_GETREGS, 1381, 0, 0x60aec330) = 0
        ptrace(PTRACE_GETFPREGS, 1381, 0, 0x60aec408) = 0
        ptrace(PTRACE_CONT, 1381, 0, SIGSEGV)   = 0
    - round and round

I hope it helps in some way.
I'm going to try mm patches now, to see if something behaves different (better if possible :)
nik.
PS: your setarch patch works, thanks!

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OK, so I've tested 2.6.18-mm2, results are:
pcap network transport seems to be broken, and doesn't compile, I had to disable it
apart from that, all of behavior described before remains the same, nothing behaves neither better, nor worse...
n.

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Attached patch should fix it (it's against git head but should be the same thing).

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade

uml: make pcap driver compile again
From: Paolo 'Blaisorblade' Giarrusso <[email protected]>

Fix this error:
arch/um/drivers/pcap_user.c:124: error: conflicting type qualifiers for ‘pcap_user_info’ arch/um/drivers/pcap_user.h:18: error: previous declaration of ‘pcap_user_info’ was here

the definition recently became const.

Index: linux-2.6.git/arch/um/drivers/pcap_user.h
===================================================================
@@ -15,7 +15,7 @@ struct pcap_data {
 	void *dev;
 };
 
-extern struct net_user_info pcap_user_info;
+extern const struct net_user_info pcap_user_info;
 
 extern int pcap_user_read(int fd, void *buf, int len, struct pcap_data *pri);
 

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Since you've said that that patch does not fix pcap compilation, post the compilation error (both with and without the patch) so I know what happens there. Assuming that pcap compiles on your system for stable kernels (i.e. libpcap.a is installed), as you imply in your report.

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
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Hello Paolo,
I've spent half a day today trying all variants, and well, I'm no longer able to reproduce the problem :(
In fact now APPLYING your patch seems to cause the problem, which is of course weird.
So please consider this false bugreport until I'm able to find out how the hell did I manage to do it.
If I'm reading my confusing posts to this list, I'm starting to feel a bit stupid, sorry for them :-/
I'll certainly have to track all my attempts and compilations, as I'm having quite a mess in it then...
n.

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The patch will cause the problem if applied without another certain patch, so it means that 2.6.18-mm2 does not contain it. I can't be sure without the compilation error but I can guess it is the problem.

Do not worry, it happens - you've falsified your bugreport, normally someone else must do it (in one occasion I've received configuration files from the wrong machine, i.e. "this is my host config" while it was the guest one, wondered a bit and then pointed kindly this possibility to the poster, who recognized promptly his error).

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
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That's it!
-mm3 kernel is causing this problem, and Your patch indeed fixes it! I completely forgot that I was also trying mm patches and I certainly mixed them with Your patches :-/
at least I'm glad that I now know where the problem was...

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Fine!
Next time, however, you'll save your time if you cut'n'paste the gcc output and do "head Makefile" (brighter variations are possible, but that should work if you don't use git) to get the exact version string. I don't want to criticize, just to give you a tip :-) !

Bye

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
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Hi,
thanks for tips! actually I'm really glad for them as I'd like to help in any way and later even join development if I'll be able to do sth ;). Actually there are two questions regarding to this I have:
1) You mentioned GIT, do You use it? or Jeff? I haven't noticed any UML git branch...
2) I'm still worried about this halt problem on amd64, can You give me some tips I could track it down?? I't only thing which is preventing me from migrating users on new machine, otherwise it seems to be working great (but of course I'm still really looking forward for full SKAS ;)) thanks a lot for Your patience with me...
nik

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I use it, I was thinking about the Linus' git branch. If you use that, head Makefile won't tell you the whole truth (it won't tell you which commit you are on).

Right, we queue our patches with quilt and send them through -mm. Jeff publishes his *development* quilt tree on UML homepage.

A 100%-cpu loop without messages is difficult to diagnose - the first answer is "check if SMP is enabled on that UML binary, disable SMP, and see if it disappears". SMP does not work; when Jeff will announce "SMP support ready" then it will be possible to start using it again.

Otherwise, if you enable debug info and recompile it, try attaching gdb to the process using 100% cpu (type gdb $vmlinux_binary $pid) and then type bt at the prompt. While recompiling, under "Kernel hacking" try enabling every debug option (excluding "kobject debugging" and a few others) - this is what I have on testing kernels, for reference (comes from a GIT head kernel):

CONFIG_PRINTK_TIME=y
CONFIG_ENABLE_MUST_CHECK=y
# CONFIG_UNUSED_SYMBOLS is not set
CONFIG_DEBUG_KERNEL=y
CONFIG_LOG_BUF_SHIFT=15
CONFIG_DETECT_SOFTLOCKUP=y
CONFIG_SCHEDSTATS=y
CONFIG_DEBUG_SLAB=y
CONFIG_DEBUG_SLAB_LEAK=y
CONFIG_DEBUG_RT_MUTEXES=y
CONFIG_DEBUG_PI_LIST=y
CONFIG_RT_MUTEX_TESTER=y
CONFIG_DEBUG_SPINLOCK=y
CONFIG_DEBUG_MUTEXES=y
CONFIG_DEBUG_RWSEMS=y
CONFIG_DEBUG_SPINLOCK_SLEEP=y
CONFIG_DEBUG_LOCKING_API_SELFTESTS=y
# CONFIG_DEBUG_KOBJECT is not set
CONFIG_DEBUG_INFO=y
# CONFIG_DEBUG_FS is not set
CONFIG_DEBUG_VM=y
CONFIG_DEBUG_LIST=y
CONFIG_FRAME_POINTER=y
CONFIG_UNWIND_INFO=y
# CONFIG_FORCED_INLINING is not set
CONFIG_RCU_TORTURE_TEST=m
# CONFIG_CMDLINE_ON_HOST is not set
# CONFIG_PT_PROXY is not set
# CONFIG_GCOV is not set

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
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I don't. I use quilt, although I occasionally construct a git tree when there's something in -linux that I need to look at.

The hang happens at the very end of the shutdown sequence, after all services have been turned off?

IIRC, you said that stracing UML shows a VTALRM-handling loop and that the UML is consuming all available CPU. Those two statements are not consistent, AFIAK, since there should be no busy loops in UML (although I can imagine bugs which could induce one) and the VTALRM loop is the sign of the idle loop, which isn't busy.

So, could you confirm all this, and also get a stack trace from the hang?

Jeff

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You really changed long to int? In this case, you may only have introduced a bigger overflow.
Jeff, I remember vaguely a recent (>=2.6.17) patch about udelay fixing a misbehaviour, would you please complete my recollection and verify the interaction with this?

Also, since we take __const_udelay and __udelay() from asm/arch/delay.h:
(for i386):

#define udelay(n) (__builtin_constant_p(n) ? \
        ((n) > 20000 ? __bad_udelay() : __const_udelay((n) * 0x10c6ul)) : \
        __udelay(n))

#define ndelay(n) (__builtin_constant_p(n) ? \
       ((n) > 20000 ? __bad_ndelay() : __const_udelay((n) * 5ul)) : \
       __ndelay(n))

We then do _not_ take these definitions:
arch/i386/lib/delay.c:

void __udelay(unsigned long usecs)

{
        __const_udelay(usecs * 0x000010c7); /* 2**32 / 1000000 (rounded up) */
}

void __ndelay(unsigned long nsecs)

{
        __const_udelay(nsecs * 0x00005); /* 2**32 / 1000000000 (rounded up) */
}

instead for us __udelay and __const_udelay match, which is not likely to help at all. Their code is correct because the asm "mull" call divides the obtained product by 2^32 by throwing away the 32 low bits (i.e. EAX, since the mull result is in EDX:EAX), and the meaning of this is to do the division only at the very end (to improve accuracy).

This bug is here at least since 2.6.16.
Suggested solution:
1) have _our own_ delay.h, to avoid depending on subarchs' changes
2) first avoid playing so complex tricks, then maybe copy their implementation (note it is slightly different already among x86 and x86_64).

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
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Yes, I'm aware of that, I just wanted to try how i386 variant behaves. btw I just tried gdb to find out why i386 UML on x86_64 host hangs just at the beginning, and it turned out to be same problem with __const_udelay. well, it's not a big surprise now I guess. So if You need further testing, please feel free to post patches etc ;) regards
nik.

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There were two problems.

One was that the declaration and definition of most arch __const_udelay were mismatched. It was simply a name mismatch, would not cause miscompilation, but did cause conceptual problems:

arch/i386/lib/delay.c:
inline void __const_udelay(unsigned long xloops)

include/asm-i386/delay.h:

	extern void __const_udelay(unsigned long usecs);

I'm also somewhat interested in how something that's defined inline in a C file will be accessible to other files such that an extern declaration would be needed.

The second problem (IIRC) was the mismatch you noted, although I can't find that part of the patch any more. I didn't understand the magic constants in asm-i386/delay.h, and didn't see the comments in arch/i386/lib/delay.c, which might have helped.

This sounds reasonable.

Jeff

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Argh... I thought I marked that as "for developers" (there was a single release for 2.6.18-rc4, but separate ones for 2.6.18...) - that patch (fremap) is IMHO very stable, but I've been its only tester till now.

When 64bit guests try using /proc/mm they'll crash, as explained, so you can skip testing/reporting this case.

...

Ok, you are the second user reporting this problem. Some option is not being parsed correctly by UML, so it is passed to init.

So you obtain this as a regression in -bb1... try unapplying patches/tls/x86-64-support.diff (you find separate patches in the broken-out folder in the archive).

Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade

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Yes, You're right, reverting this particular patch fixed the problem, so it boots now...
All other problems (halt problem with x86_64 guest and hang trying to run i386 guest) persist
Is there something else I could try to fix those or find where the problem is?
thanks in advance!
nik.

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