Re: [Xen-devel] [PATCH] x86_emulate: properly do IP updates and other side effects on success

[Fabio Fantoni <fabio.fantoni@xxxxxxx>]

Il 07/08/2014 10:30, Jan Beulich ha scritto:
> The two MMX/SSE/AVX code blocks failed to update IP properly, and these
> as well as get_reg_refix(), which "manually" updated IP so far, failed
> to do the TF and RF processing needed at the end of successfully
> emulated instructions.
>
> Reported-by: Andrei LUTAS <vlutas@xxxxxxxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Tested-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
Thanks for the patch, I tested it to see if solves also qxl on linux 
domUs problem but with this patch the domU crashes and I cannot get a 
backtrace or specific errors.
xl create is ok, gdb on qemu close on domU's crash without having 
backtrace and in xl dmesg I not saw errors.
Setting preserve always in xl cfg I can only see that crash and do a 
core dump but I not know how to use it to take a backtrace or any other 
useful information.
Someone can explain how to debug the problem for post all useful 
informations please?
In attachment for now I put xl -vvv create and xl dmesg output.

Thanks for any reply and sorry for my bad english.

> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -720,29 +720,26 @@ do{ uint8_t stub[] = { _bytes, 0xc3 };
>       put_fpu(&fic);                                                      \
>   } while (0)
>   
> -static unsigned long __get_rep_prefix(
> -    struct cpu_user_regs *int_regs,
> -    struct cpu_user_regs *ext_regs,
> +static unsigned long _get_rep_prefix(
> +    const struct cpu_user_regs *int_regs,
>       int ad_bytes)
>   {
> -    unsigned long ecx = ((ad_bytes == 2) ? (uint16_t)int_regs->ecx :
> -                         (ad_bytes == 4) ? (uint32_t)int_regs->ecx :
> -                         int_regs->ecx);
> -
> -    /* Skip the instruction if no repetitions are required. */
> -    if ( ecx == 0 )
> -        ext_regs->eip = int_regs->eip;
> -
> -    return ecx;
> +    return (ad_bytes == 2) ? (uint16_t)int_regs->ecx :
> +           (ad_bytes == 4) ? (uint32_t)int_regs->ecx :
> +           int_regs->ecx;
>   }
>   
>   #define get_rep_prefix() ({                                             \
>       unsigned long max_reps = 1;                                         \
>       if ( rep_prefix() )                                                 \
> -        max_reps = __get_rep_prefix(&_regs, ctxt->regs, ad_bytes);      \
> +        max_reps = _get_rep_prefix(&_regs, ad_bytes);                   \
>       if ( max_reps == 0 )                                                \
> -        goto done;                                                      \
> -   max_reps;                                                            \
> +    {                                                                   \
> +        /* Skip the instruction if no repetitions are required. */      \
> +        dst.type = OP_NONE;                                             \
> +        goto writeback;                                                 \
> +    }                                                                   \
> +    max_reps;                                                           \
>   })
>   
>   static void __put_rep_prefix(
> @@ -3921,7 +3918,8 @@ x86_emulate(
>           if ( !rc && (b & 1) && (ea.type == OP_MEM) )
>               rc = ops->write(ea.mem.seg, ea.mem.off, mmvalp,
>                               ea.bytes, ctxt);
> -        goto done;
> +        dst.type = OP_NONE;
> +        break;
>       }
>   
>       case 0x20: /* mov cr,reg */
> @@ -4188,7 +4186,8 @@ x86_emulate(
>           if ( !rc && (b != 0x6f) && (ea.type == OP_MEM) )
>               rc = ops->write(ea.mem.seg, ea.mem.off, mmvalp,
>                               ea.bytes, ctxt);
> -        goto done;
> +        dst.type = OP_NONE;
> +        break;
>       }
>   
>       case 0x80 ... 0x8f: /* jcc (near) */ {

Attachment: xl-vvv-create.txt
Description: Text document

Attachment: xl-dmesg.txt
Description: Text document

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