Re: [PATCH v7 6/8] irqchip/gicv2m: implement msi_doorbell_info callback

[Eric Auger]

Marc,
On 04/20/2016 07:56 PM, Marc Zyngier wrote:
> On Wed, 20 Apr 2016 14:33:17 +0200
> Eric Auger <eric.auger@xxxxxxxxxx> wrote:
> 
>> Marc,
>> On 04/20/2016 11:27 AM, Marc Zyngier wrote:
>>> On 19/04/16 18:13, Eric Auger wrote:
>>>> This patch implements the msi_doorbell_info callback in the
>>>> gicv2m driver.
>>>>
>>>> The driver now is able to return its doorbell characteristics
>>>> (base, size, prot). A single doorbell is exposed.
>>>>
>>>> This will allow the msi layer to iommu_map this doorbell when
>>>> requested.
>>>>
>>>> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
>>>>
>>>> ---
>>>>
>>>> v7: creation
>>>> ---
>>>>  drivers/irqchip/irq-gic-v2m.c | 32 +++++++++++++++++++++++++++++++-
>>>>  1 file changed, 31 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/irqchip/irq-gic-v2m.c b/drivers/irqchip/irq-gic-v2m.c
>>>> index 28f047c..54690b9 100644
>>>> --- a/drivers/irqchip/irq-gic-v2m.c
>>>> +++ b/drivers/irqchip/irq-gic-v2m.c
>>>> @@ -24,6 +24,8 @@
>>>>  #include <linux/of_pci.h>
>>>>  #include <linux/slab.h>
>>>>  #include <linux/spinlock.h>
>>>> +#include <linux/percpu.h>
>>>> +#include <linux/iommu.h>
>>>>  
>>>>  /*
>>>>  * MSI_TYPER:
>>>> @@ -64,6 +66,7 @@ struct v2m_data {
>>>>  	u32 nr_spis;		/* The number of SPIs for MSIs */
>>>>  	unsigned long *bm;	/* MSI vector bitmap */
>>>>  	u32 flags;		/* v2m flags for specific implementation */
>>>> +	struct irq_chip_msi_doorbell_info doorbell_info;
>>>>  };
>>>>  
>>>>  static void gicv2m_mask_msi_irq(struct irq_data *d)
>>>> @@ -105,6 +108,16 @@ static void gicv2m_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
>>>>  		msg->data -= v2m->spi_start;
>>>>  }
>>>>  
>>>> +static const struct irq_chip_msi_doorbell_info *
>>>> +gicv2m_msi_doorbell_info(struct irq_data *data)
>>>> +{
>>>> +	struct v2m_data *v2m = irq_data_get_irq_chip_data(data);
>>>> +
>>>> +	if (!v2m)
>>>> +		return NULL;
>>>
>>> How can this ever be NULL? I think you can drop that test.
>> OK
>>>
>>>> +	return (const struct irq_chip_msi_doorbell_info *)(&v2m->doorbell_info);
>>>
>>> Please don't do that. Use "const" in the functions that are using
>>> irq_chip_msi_doorbell_info, but do not make this "const" here.
>> It definitively compiles without casting so obviously this is not needed
>> but is there any other wrong thing I don't see?
>> we still want this function to return a pointer to a const?
> 
> I don't think we can return a const pointer, because it is obviously
> not (the memory has been kmalloc'ed, and you've written to it, so it is
> not really "read-only").
I see what you are afraid of now and I will remove it; will ask some
compiler guys ;-)

Have a nice evening

Eric

> 
> Maybe I'm being overly zealous, but I've seen compilers taking amazing
> shortcuts when offered a const qualifier...
> 
>>>
>>>> +}
>>>> +
>>>>  static struct irq_chip gicv2m_irq_chip = {
>>>>  	.name			= "GICv2m",
>>>>  	.irq_mask		= irq_chip_mask_parent,
>>>> @@ -112,6 +125,7 @@ static struct irq_chip gicv2m_irq_chip = {
>>>>  	.irq_eoi		= irq_chip_eoi_parent,
>>>>  	.irq_set_affinity	= irq_chip_set_affinity_parent,
>>>>  	.irq_compose_msi_msg	= gicv2m_compose_msi_msg,
>>>> +	.msi_doorbell_info	= gicv2m_msi_doorbell_info,
>>>>  };
>>>>  
>>>>  static int gicv2m_irq_gic_domain_alloc(struct irq_domain *domain,
>>>> @@ -247,6 +261,7 @@ static void gicv2m_teardown(void)
>>>>  
>>>>  	list_for_each_entry_safe(v2m, tmp, &v2m_nodes, entry) {
>>>>  		list_del(&v2m->entry);
>>>> +		free_percpu(v2m->doorbell_info.percpu_doorbells);
>>>>  		kfree(v2m->bm);
>>>>  		iounmap(v2m->base);
>>>>  		of_node_put(to_of_node(v2m->fwnode));
>>>> @@ -299,6 +314,7 @@ static int __init gicv2m_init_one(struct fwnode_handle *fwnode,
>>>>  {
>>>>  	int ret;
>>>>  	struct v2m_data *v2m;
>>>> +	struct irq_chip_msi_doorbell __percpu *doorbell;
>>>>  
>>>>  	v2m = kzalloc(sizeof(struct v2m_data), GFP_KERNEL);
>>>>  	if (!v2m) {
>>>> @@ -311,11 +327,23 @@ static int __init gicv2m_init_one(struct fwnode_handle *fwnode,
>>>>  
>>>>  	memcpy(&v2m->res, res, sizeof(struct resource));
>>>>  
>>>> +	v2m->doorbell_info.percpu_doorbells =
>>>> +		alloc_percpu(struct irq_chip_msi_doorbell);
>>>> +	if (WARN_ON(!v2m->doorbell_info.percpu_doorbells)) {
>>>> +		ret = -ENOMEM;
>>>> +		goto err_free_v2m;
>>>> +	}
>>>> +	doorbell = per_cpu_ptr(v2m->doorbell_info.percpu_doorbells, 0);
>>>> +	doorbell->base = v2m->res.start;
>>>> +	doorbell->size = 4;
>>>> +	doorbell->prot = IOMMU_WRITE;
>>>
>>> You probably need to also have something that says IOMMU_DEVICE or
>>> something similar, because I'm afraid you're getting a memory mapping
>>> here. I've had a quick look at the two other series, but couldn't find
>>> anything that would force the memory attributes.
>> Yes you're right I currently just enforce the direction (which is
>> checked against what VFIO user registered). Do you refer to IOMMU_MMIO,
>> latterly proposed on the ML. In the positive, yes I intend to add it
>> once it gets upstreamed.
> 
> Yeah, Robin's patches should become a dependency here, because there is
> absolutely no guarantee that the device write to the doorbell won't be
> treated a normal cacheable memory, with disastrous effects.
> 
> Thanks,
> 
> 	M.
>