Re: [PATCH 1/5] x86-32: Split cache flush handler from simd handler

[Brian Gerst <brgerst@gmail.com>]

On Fri, Mar 19, 2010 at 6:33 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 03/18/2010 11:20 AM, Brian Gerst wrote:
>> Make the cache flush handler a seperate function, and use
>> an alternative to call the appropriate handler.
>>
>> +#ifdef CONFIG_X86_32
>> +dotraplinkage void
>> +do_cache_flush_error(struct pt_regs *regs, long error_code)
>> +{
>> +     conditional_sti(regs);
>> +
>> +     /*
>> +      * Handle strange cache flush from user space exception.
>> +      * This is undocumented behaviour.
>> +      */
>> +     if (regs->flags & X86_VM_MASK) {
>> +             handle_vm86_fault((struct kernel_vm86_regs *)regs, error_code);
>> +             return;
>> +     }
>> +     current->thread.trap_no = 19;
>> +     current->thread.error_code = error_code;
>> +     die_if_kernel("cache flush denied", regs, error_code);
>> +     force_sig(SIGSEGV, current);
>> +}
>> +#endif
>
> Does anyone have *any idea* what processor this applies to?  I've
> tracked the code back all the way to the original inclusion in the
> kernel, and there isn't even the slightest hint.
>
> The comment, of course, is a great example on how *not* to write
> comments... it should have mentioned the CPU in question.

This thread appears to describe the problem:
http://marc.info/?t=104960872800014&r=1&w=2

And the initial patch:
http://marc.info/?l=linux-kernel&m=104960870106838&w=2

It looks like to me, that an AMD 486 clone has an erratum where the
invd instruction from userspace generates exception 19 (13 hex)
instead of #GP (13 dec).

--
Brian Gerst