Re: [Xen-devel] [PATCH v2 4/9] x86/HVM: move NOFLUSH handling out of hvm_set_cr3()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.09.2019 21:31, Andrew Cooper wrote:
> On 17/09/2019 07:15, Jan Beulich wrote:
>> --- a/xen/arch/x86/hvm/hvm.c
>> +++ b/xen/arch/x86/hvm/hvm.c
>> @@ -2282,12 +2287,11 @@ int hvm_set_cr0(unsigned long value, boo
>>      return X86EMUL_OKAY;
>>  }
>>  
>> -int hvm_set_cr3(unsigned long value, bool may_defer)
>> +int hvm_set_cr3(unsigned long value, bool noflush, bool may_defer)
>>  {
>>      struct vcpu *v = current;
>>      struct page_info *page;
>>      unsigned long old = v->arch.hvm.guest_cr[3];
>> -    bool noflush = false;
>>  
>>      if ( may_defer && 
>> unlikely(v->domain->arch.monitor.write_ctrlreg_enabled &
>>                                 monitor_ctrlreg_bitmask(VM_EVENT_X86_CR3)) )
>> @@ -2299,17 +2303,12 @@ int hvm_set_cr3(unsigned long value, boo
>>              /* The actual write will occur in hvm_do_resume(), if 
>> permitted. */
>>              v->arch.vm_event->write_data.do_write.cr3 = 1;
>>              v->arch.vm_event->write_data.cr3 = value;
>> +            v->arch.vm_event->write_data.cr3_noflush = noflush;
> 
> ... this, which I'm pretty sure breaks the reporting of noflush mov to
> cr3's.  The semantics of the VMI hook is "the guest tried to write this
> value to cr3", which should include the noflush bit in its architectural
> position.  I suspect it also breaks a reply with the noflush bit set,
> because I don't see any way that is fed back from the introspecting agent.

hvm_monitor_cr() zaps the bit off the reported value. I wonder
whether the patch here should include removing this zapping, as
being redundant now. I don't think though that the patch alters
behavior in this regard.

> CC'ing the Introspection maintainers for their view.

I'll wait for their feedback anyway, before making any possible
change to the patch.

Jan

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