Re: [Xen-devel] [PATCH v2 1/6] x86/xpti: avoid copying L4 page table contents when possible

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.03.18 at 08:01, <jgross@xxxxxxxx> wrote:
> On 05/03/18 17:43, Jan Beulich wrote:
>>>>> On 02.03.18 at 09:13, <jgross@xxxxxxxx> wrote:
>>> --- a/xen/arch/x86/mm.c
>>> +++ b/xen/arch/x86/mm.c
>>> @@ -509,6 +509,8 @@ void make_cr3(struct vcpu *v, mfn_t mfn)
>>>  
>>>  void write_ptbase(struct vcpu *v)
>>>  {
>>> +    get_cpu_info()->root_pgt_changed = this_cpu(root_pgt) && is_pv_vcpu(v) 
>>> &&
>>> +                                       !is_pv_32bit_vcpu(v);
>> 
>> Why is_pv_vcpu() when you already check is_pv_32bit_vcpu()?
> 
> I check !is_pv_32bit_vcpu() to catch 64-bit pv-domains only.

Oh, I'm sorry - For whatever reason I've ignored the ! there.

>> And don't you need to disallow updating L4s of running guests now
>> (which is a bad idea anyway)?
> 
> Yes, I should do that.

But please do this as a separate change, as strictly speaking this is
a behavioral change that we can't allow. But I think we simply need
to accept this (and perhaps uniformly for all page table levels).

Jan


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