Re: [v2] KVM: VMX: Fix commit which broke PML

[Kai Huang <kai.huang@linux.intel.com>]

Hi Paolo,

Thanks for applying! I am really sorry that I forgot to delete the line 
that clears SECONDARY_EXEC_ENABLE_PML bit in vmx_disable_pml, which is 
renamed to vmx_destroy_pml_buffer now.
It won't impact functionality but to make the function consistent, would 
you also do below? Sorry for such negligence!

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 89f4fa2..ef4ca76 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -7826,8 +7826,6 @@ static void vmx_destroy_pml_buffer(struct vcpu_vmx 
*vmx)
         ASSERT(vmx->pml_pg);
         __free_page(vmx->pml_pg);
         vmx->pml_pg = NULL;
-
-       vmcs_clear_bits(SECONDARY_VM_EXEC_CONTROL, 
SECONDARY_EXEC_ENABLE_PML);
  }

Thanks,
-Kai

On 11/04/2015 08:00 PM, Paolo Bonzini wrote:
>
> On 04/11/2015 06:46, Kai Huang wrote:
>> I found PML was broken since below commit:
>>
>> 	commit feda805fe7c4ed9cf78158e73b1218752e3b4314
>> 	Author: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>> 	Date:   Wed Sep 9 14:05:55 2015 +0800
>>
>> 	KVM: VMX: unify SECONDARY_VM_EXEC_CONTROL update
>>
>> 	Unify the update in vmx_cpuid_update()
>>
>> 	Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
>> 	[Rewrite to use vmcs_set_secondary_exec_control. - Paolo]
>> 	Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>>
>> The reason is in above commit vmx_cpuid_update calls vmx_secondary_exec_control,
>> in which currently SECONDARY_EXEC_ENABLE_PML bit is cleared unconditionally (as
>> PML is enabled in creating vcpu). Therefore if vcpu_cpuid_update is called after
>> vcpu is created, PML will be disabled unexpectedly while log-dirty code still
>> thinks PML is used.
>>
>> Fix this by clearing SECONDARY_EXEC_ENABLE_PML in vmx_secondary_exec_control
>> only when PML is not supported or not enabled (!enable_pml). This is more
>> reasonable as PML is currently either always enabled or disabled. With this
>> explicit updating SECONDARY_EXEC_ENABLE_PML in vmx_enable{disable}_pml is not
>> needed so also rename vmx_enable{disable}_pml to vmx_create{destroy}_pml_buffer.
>>
>> Signed-off-by: Kai Huang <kai.huang@linux.intel.com>
>>
>> ---
>>
>> v1->v2: Fix this by following Paolo's suggestion. It's better to not to clear
>> SECONDARY_EXEC_ENABLE_PML in vmx_secondary_exec_control unconditionally but only
>> clear it when PML is not supported or enabled.
>>
>> ---
>>   arch/x86/kvm/vmx.c | 15 +++++++--------
>>   1 file changed, 7 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 2ac11641..89f4fa2 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -4718,8 +4718,9 @@ static u32 vmx_secondary_exec_control(struct vcpu_vmx *vmx)
>>   	   a current VMCS12
>>   	*/
>>   	exec_control &= ~SECONDARY_EXEC_SHADOW_VMCS;
>> -	/* PML is enabled/disabled in creating/destorying vcpu */
>> -	exec_control &= ~SECONDARY_EXEC_ENABLE_PML;
>> +
>> +	if (!enable_pml)
>> +		exec_control &= ~SECONDARY_EXEC_ENABLE_PML;
>>   
>>   	/* Currently, we allow L1 guest to directly run pcommit instruction. */
>>   	exec_control &= ~SECONDARY_EXEC_PCOMMIT;
>> @@ -7804,7 +7805,7 @@ static void vmx_get_exit_info(struct kvm_vcpu *vcpu, u64 *info1, u64 *info2)
>>   	*info2 = vmcs_read32(VM_EXIT_INTR_INFO);
>>   }
>>   
>> -static int vmx_enable_pml(struct vcpu_vmx *vmx)
>> +static int vmx_create_pml_buffer(struct vcpu_vmx *vmx)
>>   {
>>   	struct page *pml_pg;
>>   
>> @@ -7817,12 +7818,10 @@ static int vmx_enable_pml(struct vcpu_vmx *vmx)
>>   	vmcs_write64(PML_ADDRESS, page_to_phys(vmx->pml_pg));
>>   	vmcs_write16(GUEST_PML_INDEX, PML_ENTITY_NUM - 1);
>>   
>> -	vmcs_set_bits(SECONDARY_VM_EXEC_CONTROL, SECONDARY_EXEC_ENABLE_PML);
>> -
>>   	return 0;
>>   }
>>   
>> -static void vmx_disable_pml(struct vcpu_vmx *vmx)
>> +static void vmx_destroy_pml_buffer(struct vcpu_vmx *vmx)
>>   {
>>   	ASSERT(vmx->pml_pg);
>>   	__free_page(vmx->pml_pg);
>> @@ -8706,7 +8705,7 @@ static void vmx_free_vcpu(struct kvm_vcpu *vcpu)
>>   	struct vcpu_vmx *vmx = to_vmx(vcpu);
>>   
>>   	if (enable_pml)
>> -		vmx_disable_pml(vmx);
>> +		vmx_destroy_pml_buffer(vmx);
>>   	free_vpid(vmx->vpid);
>>   	leave_guest_mode(vcpu);
>>   	vmx_load_vmcs01(vcpu);
>> @@ -8790,7 +8789,7 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>>   	 * for the guest, etc.
>>   	 */
>>   	if (enable_pml) {
>> -		err = vmx_enable_pml(vmx);
>> +		err = vmx_create_pml_buffer(vmx);
>>   		if (err)
>>   			goto free_vmcs;
>>   	}
>>
>
> Applied, thanks!
>
> Paolo
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