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

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

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?

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);
>