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

[Brian Gerst]

On Fri, Mar 19, 2010 at 6:33 PM, H. Peter Anvin <hpa@xxxxxxxxx> 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)
>> +{
>> + Â Â conditional_sti(regs);
>> +
>> + Â Â /*
>> + Â Â Â* Handle strange cache flush from user space exception.
>> + Â Â Â* This is undocumented behaviour.
>> + Â Â Â*/
>> + Â Â if (regs->flags & X86_VM_MASK) {
>> + Â Â Â Â Â Â handle_vm86_fault((struct kernel_vm86_regs *)regs, error_code);
>> + Â Â Â Â Â Â return;
>> + Â Â }
>> + Â Â current->thread.trap_no = 19;
>> + Â Â current->thread.error_code = error_code;
>> + Â Â die_if_kernel("cache flush denied", regs, error_code);
>> + Â Â force_sig(SIGSEGV, current);
>> +}
>> +#endif
>
> Does anyone have *any idea* what processor this applies to? ÂI'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
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