[uml-devel] Re: Hostfs and Humfs

[BlaisorBlade <blaisorblade_spam@yahoo.it>]

Alle 20:40, lunedì 5 aprile 2004, hai scritto:
> BTW, if you do IRC, you will have a better idea of what exactly I'm doing
> if you hang on the UML IRC channel - #uml on oftc.net.  I'm there quite
> often, and I tend to mumble about what I'm working on at the moment.
>
> Also, would you be interested in being able to put downloads on the UML
> site rather than having them on user-linux-linux.org, which isn't as
> visible?

Sorry for answering so late, but I've been away for a week, for theoretical 
studies in computer science. For now I must decrease my UML activity since 
I'll have to solve a very hard test soon; and I cannot do that myself.

However, especially for the second question, the answer is "yes".

At least for the 2.4.25 and 2.6.4 Skas patches, which are VERY important for 
users. Especially because there are 3 bugs in most SKAS patches floating 
around:
- the SMP bug we discussed about some time ago, fixed in my last release;
- this change (the one in the 2nd one) from Ingo Molnar that everyone else 
missed:

-static int write_ldt(void __user * ptr, unsigned long bytecount, int oldmode)
+static int write_ldt(struct mm_struct * mm, void __user * ptr, unsigned long 
bytecount, int oldmode)
 {
-       struct mm_struct * mm = current->mm;
        __u32 entry_1, entry_2, *lp;
        int error;
        struct user_desc ldt_info;
@@ -195,7 +197,7 @@

        down(&mm->context.sem);
        if (ldt_info.entry_number >= mm->context.size) {
///// ---------------> NO ONE NOTICED this!
-               error = alloc_ldt(&current->mm->context,  
ldt_info.entry_number+1, 1);
+               error = alloc_ldt(&mm->context, ldt_info.entry_number+1, 1);
                if (error < 0)
                        goto out_unlock;
        }

- and finally this bug he fixed in  ldt.c

-       if (reload) {
+       if (reload && (&current->active_mm->context == pc)) {


They are perfectly, with only one issue: since there is CONFIG_PROC_MM in the 
headers, which is created by make oldconfig, but you don't have a 
user-visible option, user often miscompile the kernel (which then creates a 
"Checking for Skas3 patch ... yes Checking for /proc/mm ... no").

Also, I see no reason for which the bug with switch_mm() that involved the 
Skas patch in 2.6 should not happen also in 2.4; in 2.4.25 we have this 
check, which has never been triggered (include/asm-i386/mmu_context.h):

                if(cpu_tlbstate[cpu].active_mm != next)
                        out_of_line_bug();

So, maybe the 2.4 Skas patch could need the same change the 2.6 has in 
include/asm-i386/mmu_context.h.

However, please review and upload them by yourself. I'm actually busy at the 
moment - VERY busy.

Bye
-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729



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