linux-kernel - Re: [PATCH 3/4] x86: disallow running with 32-bit PTEs to work around erratum

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Date:	Wed, 6 Jul 2016 09:02:25 -0700
From:	Dave Hansen <dave@...1.net>
To:	Hillf Danton <hillf.zj@...baba-inc.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH 3/4] x86: disallow running with 32-bit PTEs to work around
 erratum

On 07/03/2016 09:20 PM, Hillf Danton wrote:
...
>> When we have 64-bit PTEs (64-bit mode or 32-bit PAE), we were able
>> to move the swap PTE format around to avoid these troublesome bits.
>> But, 32-bit non-PAE is tight on bits.  So, disallow it from running
>> on this hardware.  I can't imagine anyone wanting to run 32-bit
>> on this hardware, but this is the safe thing to do.
> 
> <jawoff>
> 
> Isn't this work from Mr. Tlb?

I have no idea what you mean.
>> +	if (!err)
>> +		err = check_knl_erratum();
>>
>>  	if (err_flags_ptr)
>>  		*err_flags_ptr = err ? err_flags : NULL;
>> @@ -185,3 +188,32 @@ int check_cpu(int *cpu_level_ptr, int *r
>>
>>  	return (cpu.level < req_level || err) ? -1 : 0;
>>  }
>> +
>> +int check_knl_erratum(void)
> 
> s/knl/xeon_knl/ ?

Nah.  I mean we could say xeon_phi_knl, but I don't think it's worth
worrying too much about a function called in one place and commented
heavily.

>> +	puts("This 32-bit kernel can not run on this processor due\n"
>> +	     "to a processor erratum.  Use a 64-bit kernel, or PAE.\n\n");
> 
> Give processor name to the scared readers please.

Yeah, that's a pretty good idea.  I'll be more explicit.