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

[peter <peter@randomwebstuff.com>]

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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