Re: [PATCH 2/3] kvm: add SPTE_HOST_WRITEABLE flag to the shadow ptes.

[Izik Eidus <ieidus@redhat.com>]

Marcelo Tosatti wrote:
> On Tue, Mar 31, 2009 at 03:00:03AM +0300, Izik Eidus wrote:
>   
>> this flag notify that the host physical page we are pointing to from
>> the spte is write protected, and therefore we cant change its access
>> to be write unless we run get_user_pages(write = 1).
>>
>> (this is needed for change_pte support in kvm)
>>
>> Signed-off-by: Izik Eidus <ieidus@redhat.com>
>>     
>
>   
>> @@ -547,6 +551,7 @@ static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
>>  static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
>>  {
>>  	int i, offset, nr_present;
>> +        bool reset_host_protection = 1;
>>  
>>  	offset = nr_present = 0;
>>  
>> @@ -584,9 +589,14 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
>>  
>>  		nr_present++;
>>  		pte_access = sp->role.access & FNAME(gpte_access)(vcpu, gpte);
>> +		if (!(sp->spt[i] & SPTE_HOST_WRITEABLE)) {
>> +			pte_access &= ~PT_WRITABLE_MASK;
>> +                        reset_host_protection = 0;
>> +              }
>>     
>
>                  else
>                           reset_host_protection = 1;
>                 
> Otherwise you clear SPTE_HOST_WRITEABLE for all sptes once you find a
> single one thats unset.
>
> Also mind the tabs.
>   
Yes, you are right wont work too effective ;-)


Anyway i will repost it as soon as we decide about PATCH 1/ 3 (the 
#IFDEF thing)

Thank Marcelo :-)