Date: Tue, 21 Jan 1997 20:13:45 +1000 (EST) From: Stephen McKay <syssgm@devetir.qld.gov.au> To: Mark Murray <mark@grondar.za> Cc: freebsd-current@freebsd.org, syssgm@devetir.qld.gov.au Subject: Re: VM bogon? Was: Re: NIS breakage Message-ID: <199701211013.UAA13869@ogre.devetir.qld.gov.au>
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Stephen McKay <syssgm@devetir.qld.gov.au> wrote:
>Hmm. I've just been looking at copyout(). If the target pages are not
>present, then their page table page might not be present either. In this
>case, won't the attempt to check the target pages' writability cause a
>fault? This fault would then be translated to EFAULT (Bad address) by
>copyout_fault.
In fact, I'm now so keen on my hypothesis that I've written some code.
Unfortunately, I have no -current box to test it on. Thus, if Mr Murry
wishes to risk all, the following patch may help.
** WARNING ** I have done no testing at all on this patch. ** WARNING **
--- support.s Tue Jan 21 11:48:00 1997
+++ support.s.new Tue Jan 21 19:43:35 1997
@@ -675,12 +675,17 @@
andb $0xfc,%dl
1: /* check PTE for each page */
+ leal _PTmap(%edx),%eax
+ shrl $IDXSHIFT,%eax
+ andb $0xfc,%al
+ testb $0x01,_PTmap(%eax) /* PTE Page must be VALID */
+ je 4f
movb _PTmap(%edx),%al
andb $0x07,%al /* Pages must be VALID + USERACC + WRITABLE */
cmpb $0x07,%al
je 2f
- /* simulate a trap */
+4: /* simulate a trap */
pushl %edx
pushl %ecx
shll $IDXSHIFT,%edx
There is also some harmless cruft in trap.c left over from the days before
page tables were automatically handled by the pmap routines:
--- trap.c Tue Jan 21 11:48:03 1997
+++ trap.c.new Tue Jan 21 19:50:40 1997
@@ -781,7 +781,7 @@
unsigned addr;
{
struct proc *p;
- vm_offset_t va, v;
+ vm_offset_t va;
struct vmspace *vm;
int rv;
@@ -804,8 +804,6 @@
return (1);
}
}
-
- v = trunc_page(vtopte(va));
/*
* fault the data page
Good luck!
Stephen.
help
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