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

[Eric Auger <eric.auger@linaro.org>]

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?

Eric
> 
> Eric
>> +		if (ret)
>> +			return false;
>> +
>> +		spin_lock(&dist->its.lock);
>> +		/*
>> +		 * Updating the status for all allocated LPIs. We catch
>> +		 * those LPIs that get disabled. We really don't care
>> +		 * about unmapped LPIs, as they need to be updated
>> +		 * later manually anyway once they get mapped.
>> +		 */
>> +		for_each_lpi(device, itte, kvm) {
>> +			if (itte->lpi < lpi || itte->lpi >= lpi + chunksize)
>> +				continue;
>> +
>> +			update_lpi_config(kvm, itte, prop[itte->lpi - lpi]);
>> +		}
>> +		spin_unlock(&dist->its.lock);
>> +		tsize -= chunksize;
>> +		lpi += chunksize;
>> +		propbase += chunksize;
>> +	}
>> +
>> +	return true;
>> +}
>> +
>> +/*
>> + * Scan the whole LPI pending table and sync the pending bit in there
>> + * with our own data structures. This relies on the LPI being
>> + * mapped before.
>> + */
>> +static bool its_sync_lpi_pending_table(struct kvm_vcpu *vcpu)
>> +{
>> +	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
>> +	unsigned long *pendmask = dist->its.buffer_page;
>> +	u32 nr_lpis = VITS_NR_LPIS;
>> +	gpa_t pendbase;
>> +	int lpi = 0;
>> +	struct its_itte *itte;
>> +	struct its_device *device;
>> +	int ret;
>> +	int lpi_bit, nr_bits;
>> +
>> +	pendbase = BASER_BASE_ADDRESS(dist->pendbaser[vcpu->vcpu_id]);
>> +
>> +	while (nr_lpis > 0) {
>> +		nr_bits = min(nr_lpis, CHUNK_SIZE * 8);
>> +
>> +		ret = kvm_read_guest(vcpu->kvm, pendbase, pendmask,
>> +				     nr_bits / 8);
>> +		if (ret)
>> +			return false;
>> +
>> +		spin_lock(&dist->its.lock);
>> +		for_each_lpi(device, itte, vcpu->kvm) {
>> +			lpi_bit = itte->lpi - lpi;
>> +			if (lpi_bit < 0 || lpi_bit >= nr_bits)
>> +				continue;
>> +			if (test_bit(lpi_bit, pendmask))
>> +				__set_bit(vcpu->vcpu_id, itte->pending);
>> +			else
>> +				__clear_bit(vcpu->vcpu_id, itte->pending);
>> +		}
>> +		spin_unlock(&dist->its.lock);
>> +		nr_lpis -= nr_bits;
>> +		lpi += nr_bits;
>> +		pendbase += nr_bits / 8;
>> +	}
>> +
>> +	return true;
>> +}
>> +
>>  /* The distributor lock is held by the VGIC MMIO handler. */
>>  static bool handle_mmio_misc_gits(struct kvm_vcpu *vcpu,
>>  				  struct kvm_exit_mmio *mmio,
>> @@ -389,6 +506,8 @@ static const struct vgic_io_range vgicv3_its_ranges[] = {
>>  /* This is called on setting the LPI enable bit in the redistributor. */
>>  void vgic_enable_lpis(struct kvm_vcpu *vcpu)
>>  {
>> +	its_update_lpis_configuration(vcpu->kvm);
>> +	its_sync_lpi_pending_table(vcpu);
>>  }
>>  
>>  int vits_init(struct kvm *kvm)
>> @@ -400,6 +519,10 @@ int vits_init(struct kvm *kvm)
>>  	if (!dist->pendbaser)
>>  		return -ENOMEM;
>>  
>> +	its->buffer_page = kmalloc(CHUNK_SIZE, GFP_KERNEL);
>> +	if (!its->buffer_page)
>> +		return -ENOMEM;
>> +
>>  	spin_lock_init(&its->lock);
>>  
>>  	INIT_LIST_HEAD(&its->device_list);
>> @@ -442,6 +565,7 @@ void vits_destroy(struct kvm *kvm)
>>  		kfree(container_of(cur, struct its_collection, coll_list));
>>  	}
>>  
>> +	kfree(its->buffer_page);
>>  	kfree(dist->pendbaser);
>>  
>>  	its->enabled = false;
>> diff --git a/virt/kvm/arm/its-emul.h b/virt/kvm/arm/its-emul.h
>> index cc5d5ff..cbc3877 100644
>> --- a/virt/kvm/arm/its-emul.h
>> +++ b/virt/kvm/arm/its-emul.h
>> @@ -29,6 +29,9 @@
>>  
>>  #include "vgic.h"
>>  
>> +#define INTERRUPT_ID_BITS_ITS 16
>> +#define VITS_NR_LPIS (1U << INTERRUPT_ID_BITS_ITS)
>> +
>>  void vgic_enable_lpis(struct kvm_vcpu *vcpu);
>>  int vits_init(struct kvm *kvm);
>>  void vits_destroy(struct kvm *kvm);
>>
>