Re: [PATCH v6 18/24] KVM: arm64: vgic-its: Add infrastructure for table lookup

Christoffer Dall
2017-05-05T12:16:36Z

On Thu, May 04, 2017 at 01:44:38PM +0200, Eric Auger wrote:
> Add a generic scan_its_table() helper whose role consists in
> scanning a contiguous table located in guest RAM and applying
> a callback on each entry. Entries can be handled as linked lists
> since the callback may return an id offset to the next entry and
> also indicate whether the entry is the last one.
>
> Helper functions also are added to compute the device/event ID
> offset to the next DTE/ITE.
>
> compute_next_devid_offset, compute_next_eventid_offset and
> scan_table will become static in subsequent patches
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
> v5 -> v6:
> - add comments about 2d level table scan as suggested by Christoffer
> - s/lookup_table/scan_its_table
> - scan_table now return 0 if last elt found and +1 if not found
> - use int for id
> - simplify compute_next_devid/eventid_offset
>
> v4 -> v5:
> - use kvm_read_guest
>
> v3 -> v4:
> - remove static to avoid compilation warning
> - correct size computation in looup_table()
> - defines now encode the number of bits used for devid and eventid offsets
> - use BIT() - 1 to encode the max offets
> ---
> virt/kvm/arm/vgic/vgic-its.c | 92 ++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 92 insertions(+)
>
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index ea8eb6a..1db7e38 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -221,6 +221,8 @@ static struct its_ite *find_ite(struct vgic_its *its, u32 device_id,
>
> #define VITS_TYPER_IDBITS 16
> #define VITS_TYPER_DEVBITS 16
> +#define VITS_DTE_MAX_DEVID_OFFSET (BIT(14) - 1)
> +#define VITS_ITE_MAX_EVENTID_OFFSET (BIT(16) - 1)
>
> /*
> * Finds and returns a collection in the ITS collection table.
> @@ -1694,6 +1696,96 @@ int vgic_its_attr_regs_access(struct kvm_device *dev,
> return ret;
> }
>
> +u32 compute_next_devid_offset(struct list_head *h, struct its_device *dev)
> +{
> + struct its_device *next;
> + u32 next_offset;
> +
> + if (list_is_last(&dev->dev_list, h))
> + return 0;
> + next = list_next_entry(dev, dev_list);
> + next_offset = next->device_id - dev->device_id;
> +
> + return min_t(u32, next_offset, VITS_DTE_MAX_DEVID_OFFSET);
> +}
> +
> +u32 compute_next_eventid_offset(struct list_head *h, struct its_ite *ite)
> +{
> + struct its_ite *next;
> + u32 next_offset;
> +
> + if (list_is_last(&ite->ite_list, h))
> + return 0;
> + next = list_next_entry(ite, ite_list);
> + next_offset = next->event_id - ite->event_id;
> +
> + return min_t(u32, next_offset, VITS_ITE_MAX_EVENTID_OFFSET);
> +}
> +
> +/**
> + * entry_fn_t - Callback called on a table entry restore path
> + * @its: its handle
> + * @id: id of the entry
> + * @entry: pointer to the entry
> + * @opaque: pointer to an opaque data
> + *
> + * Return: < 0 on error, 0 if last element was identified, id offset to next
> + * element otherwise
> + */
> +typedef int (*entry_fn_t)(struct vgic_its *its, u32 id, void *entry,
> + void *opaque);
> +
> +/**
> + * scan_its_table - Scan a contiguous table in guest RAM and applies a function
> + * to each entry
> + *
> + * @its: its handle
> + * @base: base gpa of the table
> + * @size: size of the table in bytes
> + * @esz: entry size in bytes
> + * @start_id: the ID of the first entry in the table
> + * (non zero for 2d level tables)
> + * @fn: function to apply on each entry
> + *
> + * Return: < 0 on error, 0 if last element was identified, 1 otherwise
> + * (the last element may not be found on second level tables)
> + */
> +int scan_its_table(struct vgic_its *its, gpa_t base, int size, int esz,
> + int start_id, entry_fn_t fn, void *opaque)
> +{
> + void *entry = kzalloc(esz, GFP_KERNEL);
> + struct kvm *kvm = its->dev->kvm;
> + unsigned long len = size;
> + int id = start_id;
> + gpa_t gpa = base;
> + int ret;
> +
> + while (len > 0) {
> + int next_offset;
> + size_t byte_offset;
> +
> + ret = kvm_read_guest(kvm, gpa, entry, esz);
> + if (ret)
> + goto out;
> +
> + next_offset = fn(its, id, entry, opaque);
> + if (next_offset <= 0) {
> + ret = next_offset;
> + goto out;
> + }
> +
> + byte_offset = next_offset * esz;
> + id += next_offset;
> + gpa += byte_offset;
> + len -= byte_offset;
> + }
> + ret = 1;
> +
> +out:
> + kfree(entry);
> + return ret;
> +}
> +
> /**
> * vgic_its_save_device_tables - Save the device table and all ITT
> * into guest RAM
> --
> 2.5.5
>

This is much more readable than before. Thanks for making these
changes.

Reviewed-by: Christoffer Dall <cdall@linaro.org>