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

[Paolo Bonzini <pbonzini@redhat.com>]

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