Re: [Xen-devel] [PATCH] x86: Meltdown band-aid against malicious 64-bit PV guests

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.01.18 at 18:02, <roger.pau@xxxxxxxxxx> wrote:
> On Fri, Jan 12, 2018 at 03:19:38AM -0700, Jan Beulich wrote:
>> @@ -799,6 +982,10 @@ void __init smp_prepare_cpus(unsigned in
>>  
>>      stack_base[0] = stack_start;
>>  
>> +    if ( !setup_cpu_root_pgt(0) )
>> +        panic("No memory for root page table\n");
>> +    get_cpu_info()->pv_cr3 = __pa(per_cpu(root_pgt, 0));
> 
> Wouldn't it be helpful to have a command line option to decide whether
> to enable this feature or not?

Well, that would be an option, but falling into the optimization
category. Once the basic concept has been proven by a 2nd
party to have no obvious flaws, along with backporting some
of the improvements would be my goal to work on, but the
latter behind looking at the Spectre patches (i.e. I first want
to get all fixes sorted, and then deal with improvements).

Jan


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