Re: [PATCH v2 12/15] KVM: arm64: sync LPI configuration and pending tables

[Andre Przywara <andre.przywara@arm.com>]

Hi Eric,

On 14/08/15 13:35, Eric Auger wrote:
> On 08/14/2015 01:58 PM, Eric Auger wrote:
>> On 07/10/2015 04:21 PM, Andre Przywara wrote:
>>> The LPI configuration and pending tables of the GICv3 LPIs are held
>>> in tables in (guest) memory. To achieve reasonable performance, we
>>> cache this data in our own data structures, so we need to sync those
>>> two views from time to time. This behaviour is well described in the
>>> GICv3 spec and is also exercised by hardware, so the sync points are
>>> well known.
>>>
>>> Provide functions that read the guest memory and store the
>>> information from the configuration and pending tables in the kernel.
>>>
>>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>>> ---
>> would help to have change log between v1 -> v2 (valid for the whole series)
>>>  include/kvm/arm_vgic.h  |   2 +
>>>  virt/kvm/arm/its-emul.c | 124 ++++++++++++++++++++++++++++++++++++++++++++++++
>>>  virt/kvm/arm/its-emul.h |   3 ++
>>>  3 files changed, 129 insertions(+)
>>>
>>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>>> index 2a67a10..323c33a 100644
>>> --- a/include/kvm/arm_vgic.h
>>> +++ b/include/kvm/arm_vgic.h
>>> @@ -167,6 +167,8 @@ struct vgic_its {
>>>  	int			cwriter;
>>>  	struct list_head	device_list;
>>>  	struct list_head	collection_list;
>>> +	/* memory used for buffering guest's memory */
>>> +	void			*buffer_page;
>>>  };
>>>  
>>>  struct vgic_dist {
>>> diff --git a/virt/kvm/arm/its-emul.c b/virt/kvm/arm/its-emul.c
>>> index b9c40d7..05245cb 100644
>>> --- a/virt/kvm/arm/its-emul.c
>>> +++ b/virt/kvm/arm/its-emul.c
>>> @@ -50,6 +50,7 @@ struct its_itte {
>>>  	struct its_collection *collection;
>>>  	u32 lpi;
>>>  	u32 event_id;
>>> +	u8 priority;
>>>  	bool enabled;
>>>  	unsigned long *pending;
>>>  };
>>> @@ -70,8 +71,124 @@ static struct its_itte *find_itte_by_lpi(struct kvm *kvm, int lpi)
>>>  	return NULL;
>>>  }
>>>  
>>> +#define LPI_PROP_ENABLE_BIT(p)	((p) & LPI_PROP_ENABLED)
>>> +#define LPI_PROP_PRIORITY(p)	((p) & 0xfc)
>>> +
>>> +/* stores the priority and enable bit for a given LPI */
>>> +static void update_lpi_config(struct kvm *kvm, struct its_itte *itte, u8 prop)
>>> +{
>>> +	itte->priority = LPI_PROP_PRIORITY(prop);
>>> +	itte->enabled  = LPI_PROP_ENABLE_BIT(prop);
>>> +}
>>> +
>>> +#define GIC_LPI_OFFSET 8192
>>> +
>>> +/* We scan the table in chunks the size of the smallest page size */
>> 4kB chunks?
>>> +#define CHUNK_SIZE 4096U
>>> +
>>>  #define BASER_BASE_ADDRESS(x) ((x) & 0xfffffffff000ULL)
>>>  
>>> +static int nr_idbits_propbase(u64 propbaser)
>>> +{
>>> +	int nr_idbits = (1U << (propbaser & 0x1f)) + 1;
>>> +
>>> +	return max(nr_idbits, INTERRUPT_ID_BITS_ITS);
>>> +}
>>> +
>>> +/*
>>> + * Scan the whole LPI configuration table and put the LPI configuration
>>> + * data in our own data structures. This relies on the LPI being
>>> + * mapped before.
>>> + */
>>> +static bool its_update_lpis_configuration(struct kvm *kvm)
>>> +{
>>> +	struct vgic_dist *dist = &kvm->arch.vgic;
>>> +	u8 *prop = dist->its.buffer_page;
>>> +	u32 tsize;
>>> +	gpa_t propbase;
>>> +	int lpi = GIC_LPI_OFFSET;
>>> +	struct its_itte *itte;
>>> +	struct its_device *device;
>>> +	int ret;
>>> +
>>> +	propbase = BASER_BASE_ADDRESS(dist->propbaser);
>>> +	tsize = nr_idbits_propbase(dist->propbaser);
>>> +
>>> +	while (tsize > 0) {
>>> +		int chunksize = min(tsize, CHUNK_SIZE);
>>> +
>>> +		ret = kvm_read_guest(kvm, propbase, prop, chunksize);
>> I think you still have the spin_lock issue  since if my understanding is
>> correct this is called from
>> vgic_handle_mmio_access/vcall_range_handler/gic_enable_lpis
>> where vgic_handle_mmio_access. Or does it take another path?
>>
>> Shouldn't we create a new kvm_io_device to avoid holding the dist lock?
> 
> Sorry I forgot it was the case already. But currently we always register
> the same io ops (registration entry point being
> vgic_register_kvm_io_dev) and maybe we should have separate dispatcher
> function for dist, redit and its?

What would be the idea behind it? To have separate locks for each? I
don't think that will work, as some ITS functions are called from GICv3
register handler functions which manipulate members of the distributor
structure. So I am more in favour of dropping the dist lock in these
cases before handing off execution to ITS specific functions.

Cheers,
Andre.