[PATCH] PCI/ASPM: Reject sysfs attempts to enable states that are not covered by policy

[PATCH] PCI/ASPM: Reject sysfs attempts to enable states that are not covered by policy

[Heiner Kallweit]

When trying to enable a state that is not covered by the policy,
then the change request will be silently ignored. That's not too
nice to the user, therefore reject such attempts explicitly.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 drivers/pci/pcie/aspm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index b17e5ffd3..cd0f30ca9 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1224,11 +1224,16 @@ static ssize_t aspm_attr_store_common(struct device *dev,
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
+	u32 policy_state = policy_to_aspm_state(link);
 	bool state_enable;
 
 	if (strtobool(buf, &state_enable) < 0)
 		return -EINVAL;
 
+	/* reject attempts to enable states not covered by policy */
+	if (state_enable && state & ~policy_state)
+		return -EPERM;
+
 	down_read(&pci_bus_sem);
 	mutex_lock(&aspm_lock);
 
@@ -1241,7 +1246,7 @@ static ssize_t aspm_attr_store_common(struct device *dev,
 		link->aspm_disable |= state;
 	}
 
-	pcie_config_aspm_link(link, policy_to_aspm_state(link));
+	pcie_config_aspm_link(link, policy_state);
 
 	mutex_unlock(&aspm_lock);
 	up_read(&pci_bus_sem);
-- 
2.27.0

Re: [PATCH] PCI/ASPM: Reject sysfs attempts to enable states that are not covered by policy

[Bjorn Helgaas]

On Mon, Jul 20, 2020 at 08:08:59AM +0200, Heiner Kallweit wrote:
> When trying to enable a state that is not covered by the policy,
> then the change request will be silently ignored. That's not too
> nice to the user, therefore reject such attempts explicitly.
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
> ---
>  drivers/pci/pcie/aspm.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index b17e5ffd3..cd0f30ca9 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -1224,11 +1224,16 @@ static ssize_t aspm_attr_store_common(struct device *dev,
>  {
>  	struct pci_dev *pdev = to_pci_dev(dev);
>  	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
> +	u32 policy_state = policy_to_aspm_state(link);
>  	bool state_enable;
>  
>  	if (strtobool(buf, &state_enable) < 0)
>  		return -EINVAL;
>  
> +	/* reject attempts to enable states not covered by policy */
> +	if (state_enable && state & ~policy_state)
> +		return -EPERM;

I really like the sentiment of this patch, but I don't like the fact
that this test for states being covered by the policy is here by
itself.

There must be some place in the pcie_config_aspm_link() path that does
a similar test and silently ignores things not covered by the policy?
If we could take advantage of *that* test, we won't have to worry
about things getting out of sync if we change that test in the future.

Maybe pcie_config_aspm_link() could return -EPERM if the policy
doesn't allow the requested state, and we could just notice that here?

>  	down_read(&pci_bus_sem);
>  	mutex_lock(&aspm_lock);
>  
> @@ -1241,7 +1246,7 @@ static ssize_t aspm_attr_store_common(struct device *dev,
>  		link->aspm_disable |= state;
>  	}
>  
> -	pcie_config_aspm_link(link, policy_to_aspm_state(link));
> +	pcie_config_aspm_link(link, policy_state);
>  
>  	mutex_unlock(&aspm_lock);
>  	up_read(&pci_bus_sem);
> -- 
> 2.27.0
> 

Re: [PATCH] PCI/ASPM: Reject sysfs attempts to enable states that are not covered by policy

[Heiner Kallweit]

Am 09.09.2020 um 20:28 schrieb Bjorn Helgaas:
> On Mon, Jul 20, 2020 at 08:08:59AM +0200, Heiner Kallweit wrote:
>> When trying to enable a state that is not covered by the policy,
>> then the change request will be silently ignored. That's not too
>> nice to the user, therefore reject such attempts explicitly.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
>> ---
>>  drivers/pci/pcie/aspm.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
>> index b17e5ffd3..cd0f30ca9 100644
>> --- a/drivers/pci/pcie/aspm.c
>> +++ b/drivers/pci/pcie/aspm.c
>> @@ -1224,11 +1224,16 @@ static ssize_t aspm_attr_store_common(struct device *dev,
>>  {
>>  	struct pci_dev *pdev = to_pci_dev(dev);
>>  	struct pcie_link_state *link = pcie_aspm_get_link(pdev);
>> +	u32 policy_state = policy_to_aspm_state(link);
>>  	bool state_enable;
>>  
>>  	if (strtobool(buf, &state_enable) < 0)
>>  		return -EINVAL;
>>  
>> +	/* reject attempts to enable states not covered by policy */
>> +	if (state_enable && state & ~policy_state)
>> +		return -EPERM;
> 
> I really like the sentiment of this patch, but I don't like the fact
> that this test for states being covered by the policy is here by
> itself.
> 
> There must be some place in the pcie_config_aspm_link() path that does
> a similar test and silently ignores things not covered by the policy?
> If we could take advantage of *that* test, we won't have to worry
> about things getting out of sync if we change that test in the future.
> 
> Maybe pcie_config_aspm_link() could return -EPERM if the policy
> doesn't allow the requested state, and we could just notice that here?
> 
Oh, I just see that I missed to follow-up on this topic.

Currently pcie_config_aspm_link() is called in two versions:
1. with state argument 0
2. with state argument policy_to_aspm_state(link)

Therefore pcie_config_aspm_link() doesn't check for states not covered
by the policy. We could add a policy check, but the only use case where
this check would be needed is the call from aspm_attr_store_common().
Is this worth it? Ot better go with the check in
aspm_attr_store_common() as proposed?

In addition, based on the two types of calls to pcie_config_aspm_link(),
we could simplify usage of this function and replace the state argument
with a bool enable flag. If set, then pcie_config_aspm_link() would
internally select policy_to_aspm_state() as requested state.

>>  	down_read(&pci_bus_sem);
>>  	mutex_lock(&aspm_lock);
>>  
>> @@ -1241,7 +1246,7 @@ static ssize_t aspm_attr_store_common(struct device *dev,
>>  		link->aspm_disable |= state;
>>  	}
>>  
>> -	pcie_config_aspm_link(link, policy_to_aspm_state(link));
>> +	pcie_config_aspm_link(link, policy_state);
>>  
>>  	mutex_unlock(&aspm_lock);
>>  	up_read(&pci_bus_sem);
>> -- 
>> 2.27.0
>>