Re: [uml-devel] Memory corruption/errors?

[Bodo Stroesser <bstroesser@fujitsu-siemens.com>]

peter wrote:
> Bodo?
Hi Peter,

sorry, have been off the net for a while.
The patch *really* was quick and dirty (Was in a hurry cause I wanted to send
it before my Xmas holidays). I even forgot to make it apply with "patch -p1"!
Thus, it must be inserted with "patch -p0", then it should apply.

Sorry for that.

By the way: the patch was created against 2.6.10-rc3-mm1 + Jeff's incrementals,
which was the latest version at that time. But I guess, the patch should apply
to 2.6.9-bb4, too.

Bodo


> 
> Peter wrote:
> 
>> Hi.  Thanks for the patch.
>>
>> I am trying to apply these against 2.6.9 + bb4 (from 
>> http://www.user-mode-linux.org/~blaisorblade/patches/guest/uml-2.6.9-bb4/). 
>>   Your patch is not applying (no such file, HUNKs failing, etc).
>>
>> Do you have a version of your patch that compiles against 2.6.9-bb4? 
>> Ideally I'd like to get this working with 2.6.9-bb4 since that seems 
>> to be the 'stable' 2.6 UML guest kernel.
>>
>> Else, can you let me know what code (links to all component patches 
>> appreciated) your patch is against and I will try that.
>>
>> Regards, Peter
>>
>> Bodo Stroesser wrote:
>>
>>> I'm forwarding this to the list, because I did a "Reply to all"
>>> missing the fact, that the list wasn't CC'ed
>>>
>>> Bodo
>>>
>>> ------------------------------------------------------------------------
>>>
>>> Subject:
>>> Re: [uml-devel] Memory corruption/errors?
>>> From:
>>> Bodo Stroesser <bstroesser@fujitsu-siemens.com>
>>> Date:
>>> Thu, 23 Dec 2004 13:58:18 +0100
>>> To:
>>> Peter <peter.spamcatcher@rimuhosting.com>
>>>
>>> To:
>>> Peter <peter.spamcatcher@rimuhosting.com>
>>> CC:
>>> Jeff Dike <jdike@addtoit.com>
>>>
>>>
>>> Peter wrote:
>>>
>>>>
>>>> I really don't know what fxsr is.  But I think I have it.  My 
>>>> servers are dual proc xeons.  2.6.8.1 with skas3 v7 (mostly).
>>>>
>>>> # cat /proc/cpuinfo  | grep fxsr
>>>> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr 
>>>> pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm 
>>>> pbe cid
>>>> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr 
>>>> pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm 
>>>> pbe cid
>>>> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr 
>>>> pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm 
>>>> pbe cid
>>>> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr 
>>>> pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm 
>>>> pbe cid
>>>
>>>
>>>
>>> Yes. Here the machine tell us, that fxsr is available.
>>>
>>>>
>>>> So you can only reproduce the problem when your use the sighandler?  
>>>> But when you use your patch the problem is not triggered (even with 
>>>> the sighandler)?
>>>>
>>>> I'd be happy to try a patch.  I only have production machines at the 
>>>> moment, so I may not be able to restart one for a week or two until 
>>>> some new ones arrive.
>>>>
>>>> Regards, Peter
>>>>
>>>> Bodo Stroesser wrote:
>>>>
>>>>> Peter wrote:
>>>>>
>>>>>> I don't run TT mode UMLs.  So, no I haven't tried that.
>>>>>>
>>>>>> I don't know about the sighandler.  The program runs as it was 
>>>>>> listed. It is running on a 'regular' server (Debian, and/or WBL3) 
>>>>>> with other processes running.  And the host servers happen to be 
>>>>>> running other UMLs.  I don't know if that information helps.  
>>>>>> (i.e. can a sighandler in another process on the UML or on the 
>>>>>> host cause this problem?)
>>>>>>
>>>>>> I'd be happy to try out a skas patch - preferably if it just 
>>>>>> applied to the guest ;)  To see if it fixes things or not.
>>>>>>
>>>>>> Regards, Peter
>>>>>>
>>>>> I could try to create a patch, just for testing.
>>>>> What machine is your host? It probably has fxsr?
>>>>>
>>>>> Bodo
>>>
>>>
>>>
>>> OK. Here it is! For testing only!
>>>
>>> I've tested the patch on a XEON 2.4GHz, and AFAICS it works.
>>> But no guarantee!
>>>
>>> The errors with memtest2 no longer occur on my system.
>>>
>>> I have no machine without fxsr, thus I couldn't test that.
>>> When the patch is applied, don't forget to do
>>>     "make clean ARCH=um"
>>> before recompiling the kernel.Else you will get an
>>> inconsitent kernel that crashes.
>>>
>>> Bodo
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> From: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
>>>
>>> This patch is for testing only!
>>>
>>> It's a quick and dirty patch to verify, that wrong fp-context
>>> saving and restore really are the cause of errors in "memtest.c"
>>> It fixes the problem by:
>>>  - making have_fpx_regs accessible for other modules instead of
>>>    declaring it "static" in arch/um/os-Linux/sys-i386/registers.c
>>>  - Adding 1 to HOST_FP_SIZE to have room for the "status" (and magic)
>>>    field. Now skas.fp + skas.xfp combined have the size of
>>>    struct _fpstatus
>>>  - in arch/um/sys-i386/signal.c adding some code, that handles
>>>    the _fpstatus in sigcontext differently, depending on have_fpx_regs.
>>>    For (have_fpx_regs == 0), the _fpstatus simply is copied to/from
>>>    user from/to skas.fp. When writing to user, the status field is
>>>    created also.
>>>    For (have_fpx_regs == 1), when writing to user, the full _fpstatus
>>>    is created in skas.fp and skas.xfp, from the data found in skas.xfp.
>>>    Then it is copied to user. When reading, the full _fpstatus is read
>>>    to skas.fp and skas.xfp. Then, skas.xfp is reconstructed from this
>>>    data.
>>>
>>> ---
>>>
>>> --- arch/um/os-Linux/sys-i386/registers.c.orig    2004-12-23 
>>> 00:22:54.000000000 +0100
>>> +++ arch/um/os-Linux/sys-i386/registers.c    2004-12-23 
>>> 00:23:13.016000444 +0100
>>> @@ -17,7 +17,7 @@
>>>  static unsigned long exec_regs[HOST_FRAME_SIZE];
>>>  static unsigned long exec_fp_regs[HOST_FP_SIZE];
>>>  static unsigned long exec_fpx_regs[HOST_XFP_SIZE];
>>> -static int have_fpx_regs = 1;
>>> +int have_fpx_regs = 1;
>>>  
>>>  void init_thread_registers(union uml_pt_regs *to)
>>>  {
>>> --- arch/um/sys-i386/signal.c.orig    2004-12-23 00:17:19.000000000 
>>> +0100
>>> +++ arch/um/sys-i386/signal.c    2004-12-23 11:41:41.928379633 +0100
>>> @@ -19,15 +19,37 @@
>>>  
>>>  #include "skas.h"
>>>  
>>> +
>>> +static inline unsigned short twd_i387_to_fxsr( unsigned short twd )
>>> +{
>>> +    unsigned int tmp; /* to avoid 16 bit prefixes in the code */
>>> +
>>> +    /* Transform each pair of bits into 01 (valid) or 00 (empty) */
>>> +    tmp = ~twd;
>>> +    tmp = (tmp | (tmp>>1)) & 0x5555; /* 0V0V0V0V0V0V0V0V */
>>> +    /* and move the valid bits to the lower byte. */
>>> +    tmp = (tmp | (tmp >> 1)) & 0x3333; /* 00VV00VV00VV00VV */
>>> +    tmp = (tmp | (tmp >> 2)) & 0x0f0f; /* 0000VVVV0000VVVV */
>>> +    tmp = (tmp | (tmp >> 4)) & 0x00ff; /* 00000000VVVVVVVV */
>>> +    return tmp;
>>> +}
>>> +
>>> +#define printk printf
>>> +
>>>  static int copy_sc_from_user_skas(struct pt_regs *regs,
>>>                    struct sigcontext *from)
>>>  {
>>>        struct sigcontext sc;
>>> -    unsigned long fpregs[HOST_FP_SIZE];
>>> -    int err;
>>> +    struct _fpstate * fp = (struct _fpstate *)regs->regs.skas.fp;
>>> +    int size, err, i;
>>> +
>>> +    if (have_fpx_regs)
>>> +        size = sizeof(struct _fpstate);
>>> +    else
>>> +        size = sizeof(regs->regs.skas.fp);
>>>  
>>>      err = copy_from_user(&sc, from, sizeof(sc));
>>> -    err |= copy_from_user(fpregs, sc.fpstate, sizeof(fpregs));
>>> +    err |= copy_from_user(fp, sc.fpstate, size);
>>>      if(err)
>>>          return(err);
>>>  
>>> @@ -48,23 +70,70 @@
>>>      REGS_EFLAGS(regs->regs.skas.regs) = sc.eflags;
>>>      REGS_SS(regs->regs.skas.regs) = sc.ss;
>>>  
>>> -    err = ptrace_setfpregs(userspace_pid[0], fpregs);
>>> -    if(err < 0){
>>> -          printk("copy_sc_from_user_skas - PTRACE_SETFPREGS failed, "
>>> -               "errno = %d\n", err);
>>> -        return(1);
>>> +    if (have_fpx_regs) {
>>> +        *(unsigned short *)fp->_fxsr_env = (unsigned short)(fp->cw & 
>>> 0xffff);
>>> +        *((unsigned short *)fp->_fxsr_env + 1) = (unsigned 
>>> short)(fp->sw & 0xffff);
>>> +        *((unsigned short *)fp->_fxsr_env + 2) = 
>>> twd_i387_to_fxsr(fp->tag & 0xffff);
>>> +        *((unsigned short *)fp->_fxsr_env + 3) = (unsigned 
>>> short)(fp->cssel >> 16);
>>> +        fp->_fxsr_env[2] = fp->ipoff;
>>> +        fp->_fxsr_env[3] = fp->cssel & 0xffff;
>>> +        fp->_fxsr_env[4] = fp->dataoff;
>>> +        fp->_fxsr_env[5] = fp->datasel;
>>> +        for ( i=0; i<8; i++)
>>> +        memcpy(fp->_fxsr_st+i, fp->_st+i, sizeof(struct _fpreg));
>>>      }
>>>  
>>>      return(0);
>>>  }
>>>  
>>> +static inline unsigned long twd_fxsr_to_i387( struct _fpstate *fp)
>>> +{
>>> +    struct _fpxreg *st = fp->_fxsr_st;
>>> +    unsigned long twd = fp->_fxsr_env[1] & 0x0000fffflu;
>>> +    unsigned long tag;
>>> +    unsigned long ret = 0xffff0000lu;
>>> +    int i;
>>> +
>>> +    for ( i = 0 ; i < 8 ; i++, st++ ) {
>>> +    if ( twd & 0x1 ) {
>>> +        switch ( st->exponent & 0x7fff ) {
>>> +        case 0x7fff:
>>> +            tag = 2;
>>> +            break;
>>> +        case 0x0000:
>>> +            if ( !st->significand[0] &&
>>> +                 !st->significand[1] &&
>>> +                 !st->significand[2] &&
>>> +                 !st->significand[3] ) {
>>> +            tag = 1;
>>> +            } else {
>>> +            tag = 2;
>>> +            }
>>> +            break;
>>> +        default:
>>> +            if ( st->significand[3] & 0x8000 ) {
>>> +            tag = 0;
>>> +            } else {
>>> +            tag = 2;
>>> +            }
>>> +            break;
>>> +        }
>>> +    } else {
>>> +        tag = 3;
>>> +    }
>>> +    ret |= (tag << (2 * i));
>>> +    twd = twd >> 1;
>>> +    }
>>> +    return ret;
>>> +}
>>> +
>>>  int copy_sc_to_user_skas(struct sigcontext *to, struct _fpstate *to_fp,
>>>               struct pt_regs *regs)
>>>  {
>>>        struct sigcontext sc;
>>> -    unsigned long fpregs[HOST_FP_SIZE];
>>> +    struct _fpstate * fp = (struct _fpstate *)regs->regs.skas.fp;
>>>      struct faultinfo * fi = &current->thread.arch.faultinfo;
>>> -    int err;
>>> +    int size, i;
>>>  
>>>      sc.gs = REGS_GS(regs->regs.skas.regs);
>>>      sc.fs = REGS_FS(regs->regs.skas.regs);
>>> @@ -87,20 +156,30 @@
>>>      sc.err = fi->error_code;
>>>      sc.trapno = fi->trap_no;
>>>  
>>> -    err = ptrace_getfpregs(userspace_pid[0], fpregs);
>>> -    if(err < 0){
>>> -          printk("copy_sc_to_user_skas - PTRACE_GETFPREGS failed, "
>>> -               "errno = %d\n", err);
>>> -        return(1);
>>> +    if (have_fpx_regs) {
>>> +        fp->cw = (unsigned long)*(unsigned short *)fp->_fxsr_env | 
>>> 0xffff0000ul;
>>> +        fp->sw = (unsigned long)*((unsigned short *)fp->_fxsr_env+1) 
>>> | 0xffff0000ul;
>>> +        fp->tag = twd_fxsr_to_i387(fp);
>>> +        fp->ipoff = fp->_fxsr_env[2];
>>> +        fp->cssel = fp->_fxsr_env[3] |
>>> +            ((unsigned long)*((unsigned short *)fp->_fxsr_env+3) << 
>>> 16);
>>> +        fp->dataoff = fp->_fxsr_env[4];
>>> +        fp->datasel = fp->_fxsr_env[5];
>>> +        fp->status = (unsigned short)(fp->sw & 0xfffful);
>>> +        fp->magic = 0;
>>> +        for ( i=0; i<8; i++)
>>> +        memcpy(fp->_st+i, fp->_fxsr_st+i, sizeof(struct _fpreg));
>>> +        size = sizeof(struct _fpstate);
>>> +    }
>>> +    else {
>>> +        *(unsigned long *)&fp->status = fp->sw;
>>> +        size = sizeof(regs->regs.skas.fp);
>>>      }
>>>      to_fp = (to_fp ? to_fp : (struct _fpstate *) (to + 1));
>>>      sc.fpstate = to_fp;
>>>  
>>> -    if(err)
>>> -          return(err);
>>> -
>>>      return(copy_to_user(to, &sc, sizeof(sc)) ||
>>> -           copy_to_user(to_fp, fpregs, sizeof(fpregs)));
>>> +           copy_to_user(to_fp, fp, size));
>>>  }
>>>  #endif
>>>  
>>> --- arch/um/kernel/skas/util/mk_ptregs-i386.c.orig    2004-12-23 
>>> 10:46:41.143243494 +0100
>>> +++ arch/um/kernel/skas/util/mk_ptregs-i386.c    2004-12-23 
>>> 11:08:01.272251951 +0100
>>> @@ -13,8 +13,9 @@
>>>      printf("#define __SKAS_PT_REGS_\n");
>>>      printf("\n");
>>>      printf("#define HOST_FRAME_SIZE %d\n", FRAME_SIZE);
>>> +    /* This needs to have space for "status", too */
>>>      printf("#define HOST_FP_SIZE %d\n", -           sizeof(struct 
>>> user_i387_struct) / sizeof(unsigned long));
>>> +           sizeof(struct user_i387_struct) / sizeof(unsigned long) + 
>>> 1);
>>>      printf("#define HOST_XFP_SIZE %d\n",             sizeof(struct 
>>> user_fxsr_struct) / sizeof(unsigned long));
>>>  
>>
>>
>>
>>
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