Re: [PATCH v5 20/22] KVM: arm64: vgic-its: Device table save/restore

Christoffer Dall
2017-04-30T20:55:40Z

On Fri, Apr 14, 2017 at 12:15:32PM +0200, Eric Auger wrote:
> This patch saves the device table entries into guest RAM.
> Both flat table and 2 stage tables are supported. DeviceId
> indexing is used.
>
> For each device listed in the device table, we also save
> the translation table using the vgic_its_save/restore_itt
> routines.
>
> On restore, devices are re-allocated and their ite are
> re-built.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
> v4 -> v5:
> - sort the device list by deviceid on device table save
> - use defines for shifts and masks
> - use abi->dte_esz
> - clatify entry sizes for L1 and L2 tables
>
> v3 -> v4:
> - use the new proto for its_alloc_device
> - compute_next_devid_offset, vgic_its_flush/restore_itt
> become static in this patch
> - change in the DTE entry format with the introduction of the
> valid bit and next field width decrease; ittaddr encoded
> on its full range
> - fix handle_l1_entry entry handling
> - correct vgic_its_table_restore error handling
>
> v2 -> v3:
> - fix itt_addr bitmask in vgic_its_restore_dte
> - addition of return 0 in vgic_its_restore_ite moved to
> the ITE related patch
>
> v1 -> v2:
> - use 8 byte format for DTE and ITE
> - support 2 stage format
> - remove kvm parameter
> - ITT flush/restore moved in a separate patch
> - use deviceid indexing
> ---
> virt/kvm/arm/vgic/vgic-its.c | 183 +++++++++++++++++++++++++++++++++++++++++--
> virt/kvm/arm/vgic/vgic.h | 7 ++
> 2 files changed, 185 insertions(+), 5 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index b02fc3f..86dfc6c 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -1682,7 +1682,8 @@ 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)
> +static u32 compute_next_devid_offset(struct list_head *h,
> + struct its_device *dev)
> {
> struct list_head *e = &dev->dev_list;
> struct its_device *next;
> @@ -1858,7 +1859,7 @@ static int vgic_its_ite_cmp(void *priv, struct list_head *a,
> return 1;
> }
>
> -int vgic_its_save_itt(struct vgic_its *its, struct its_device *device)
> +static int vgic_its_save_itt(struct vgic_its *its, struct its_device *device)
> {
> const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> gpa_t base = device->itt_addr;
> @@ -1877,7 +1878,7 @@ int vgic_its_save_itt(struct vgic_its *its, struct its_device *device)
> return 0;
> }
>
> -int vgic_its_restore_itt(struct vgic_its *its, struct its_device *dev)
> +static int vgic_its_restore_itt(struct vgic_its *its, struct its_device *dev)
> {
> const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> gpa_t base = dev->itt_addr;
> @@ -1895,12 +1896,161 @@ int vgic_its_restore_itt(struct vgic_its *its, struct its_device *dev)
> }
>
> /**
> + * vgic_its_save_dte - Save a device table entry at a given GPA
> + *
> + * @its: ITS handle
> + * @dev: ITS device
> + * @ptr: GPA
> + */
> +static int vgic_its_save_dte(struct vgic_its *its, struct its_device *dev,
> + gpa_t ptr, int dte_esz)
> +{
> + struct kvm *kvm = its->dev->kvm;
> + u64 val, itt_addr_field;
> + int ret;
> + u32 next_offset;
> +
> + itt_addr_field = dev->itt_addr >> 8;
> + next_offset = compute_next_devid_offset(&its->device_list, dev);
> + val = (1ULL << KVM_ITS_DTE_VALID_SHIFT |
> + ((u64)next_offset << KVM_ITS_DTE_NEXT_SHIFT) |

I think this implies that the next field in your ABI points to the next
offset, regardless of whether or not this is in a a level 2 or lavel 1
table. See more comments on this below (I reviewed this patch from the
bottom up).

I have a feeling this wasn't tested with 2 level device tables. Could
that be true?

> + (itt_addr_field << KVM_ITS_DTE_ITTADDR_SHIFT) |
> + (dev->nb_eventid_bits - 1));
> + val = cpu_to_le64(val);
> + ret = kvm_write_guest(kvm, ptr, &val, dte_esz);
> + return ret;
> +}
> +
> +/**
> + * vgic_its_restore_dte - restore a device table entry
> + *
> + * @its: its handle
> + * @id: device id the DTE corresponds to
> + * @ptr: kernel VA where the 8 byte DTE is located
> + * @opaque: unused
> + * @next: offset to the next valid device id
> + *
> + * Return: < 0 on error, 0 otherwise
> + */
> +static int vgic_its_restore_dte(struct vgic_its *its, u32 id,
> + void *ptr, void *opaque, u32 *next)
> +{
> + struct its_device *dev;
> + gpa_t itt_addr;
> + u8 nb_eventid_bits;
> + u64 entry = *(u64 *)ptr;
> + bool valid;
> + int ret;
> +
> + entry = le64_to_cpu(entry);
> +
> + valid = entry >> KVM_ITS_DTE_VALID_SHIFT;
> + nb_eventid_bits = (entry & KVM_ITS_DTE_SIZE_MASK) + 1;
> + itt_addr = ((entry & KVM_ITS_DTE_ITTADDR_MASK)
> + >> KVM_ITS_DTE_ITTADDR_SHIFT) << 8;
> + *next = 1;
> +
> + if (!valid)
> + return 0;
> +
> + /* dte entry is valid */
> + *next = (entry & KVM_ITS_DTE_NEXT_MASK) >> KVM_ITS_DTE_NEXT_SHIFT;
> +
> + ret = vgic_its_alloc_device(its, &dev, id,
> + itt_addr, nb_eventid_bits);
> + if (ret)
> + return ret;
> + ret = vgic_its_restore_itt(its, dev);
> +
> + return ret;
> +}
> +
> +static int vgic_its_device_cmp(void *priv, struct list_head *a,
> + struct list_head *b)
> +{
> + struct its_device *deva = container_of(a, struct its_device, dev_list);
> + struct its_device *devb = container_of(b, struct its_device, dev_list);
> +
> + if (deva->device_id < devb->device_id)
> + return -1;
> + else
> + return 1;
> +}
> +
> +/**
> * vgic_its_save_device_tables - Save the device table and all ITT
> * into guest RAM
> + *
> + * L1/L2 handling is hidden by vgic_its_check_id() helper which directly
> + * returns the GPA of the device entry
> */
> static int vgic_its_save_device_tables(struct vgic_its *its)
> {
> - return -ENXIO;
> + const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> + struct its_device *dev;
> + int dte_esz = abi->dte_esz;
> + u64 baser;
> +
> + baser = its->baser_device_table;
> +
> + list_sort(NULL, &its->device_list, vgic_its_device_cmp);
> +
> + list_for_each_entry(dev, &its->device_list, dev_list) {
> + int ret;
> + gpa_t eaddr;
> +
> + if (!vgic_its_check_id(its, baser,
> + dev->device_id, &eaddr))
> + return -EINVAL;
> +
> + ret = vgic_its_save_itt(its, dev);
> + if (ret)
> + return ret;
> +
> + ret = vgic_its_save_dte(its, dev, eaddr, dte_esz);
> + if (ret)
> + return ret;
> + }
> + return 0;
> +}
> +
> +/**
> + * handle_l1_entry - callback used for L1 entries (2 stage case)
> + *
> + * @its: its handle
> + * @id: id

IIUC, this is actually the index of the entry in the L1 table. I think
this should be clarified.

> + * @addr: kernel VA
> + * @opaque: unused
> + * @next_offset: offset to the next L1 entry: 0 if the last element
> + * was found, 1 otherwise
> + */
> +static int handle_l1_entry(struct vgic_its *its, u32 id, void *addr,
> + void *opaque, u32 *next_offset)

nit: shouldn't this be called handle_l1_device_table_entry ?

> +{
> + const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> + int l2_start_id = id * (SZ_64K / GITS_LVL1_ENTRY_SIZE);

Hmmm, is this not actually supposed to be (SZ_64K / abi->dte_esz) ?

> + u64 entry = *(u64 *)addr;
> + int ret, ite_esz = abi->ite_esz;

Should this be ite_esz or dte_esz?

> + gpa_t gpa;

nit: put declarations with initialization on separate lines.

> +
> + entry = le64_to_cpu(entry);
> + *next_offset = 1;

I think you could attach a comment here saying that level 1 tables have
to be scanned entirely.

But this also reminds me. Does that mean that the next field in the DTE
in your documented ABI format points to the next DTE within that level-2
table, or does it point across to different level-2 tables? I think
this needs to be clarified in the ABI unless I'm missing something.

> +
> + if (!(entry & BIT_ULL(63)))
> + return 0;
> +
> + gpa = entry & GENMASK_ULL(51, 16);

Can you define the bit fields for the level-1 entries as well please?

> +
> + ret = lookup_table(its, gpa, SZ_64K, ite_esz,
> + l2_start_id, vgic_its_restore_dte, NULL);
> +
> + if (ret == 1) {
> + /* last entry was found in this L2 table */

maybe you should define these return codes for you table scan function,
and you wouldn't have to have a separate comment and it would be
generally easier to follow the code.

> + *next_offset = 0;
> + ret = 0;
> + }
> +
> + return ret;
> }
>
> /**
> @@ -1909,7 +2059,30 @@ static int vgic_its_save_device_tables(struct vgic_its *its)
> */
> static int vgic_its_restore_device_tables(struct vgic_its *its)
> {
> - return -ENXIO;
> + const struct vgic_its_abi *abi = vgic_its_get_abi(its);
> + u64 baser = its->baser_device_table;
> + int l1_esz, ret, l1_tbl_size = GITS_BASER_NR_PAGES(baser) * SZ_64K;

nit: put this initialization on a separate line.

> + gpa_t l1_gpa;
> +
> + l1_gpa = BASER_ADDRESS(baser);
> + if (!l1_gpa)
> + return 0;

I think you meant to check the valid bit here.

> +
> + if (baser & GITS_BASER_INDIRECT) {
> + l1_esz = 8;
> + ret = lookup_table(its, l1_gpa, l1_tbl_size, l1_esz, 0,
> + handle_l1_entry, NULL);
> + } else {
> + l1_esz = abi->dte_esz;
> + ret = lookup_table(its, l1_gpa, l1_tbl_size, l1_esz, 0,
> + vgic_its_restore_dte, NULL);
> + }
> +
> + if (ret < 0)
> + return ret;
> +
> + /* if last element was not found we have an issue here */

same comment as other patch

> + return ret ? 0 : -EINVAL;
> }
>
> static int vgic_its_save_cte(struct vgic_its *its,
> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
> index ce57fbd..9bc52ef 100644
> --- a/virt/kvm/arm/vgic/vgic.h
> +++ b/virt/kvm/arm/vgic/vgic.h
> @@ -85,6 +85,13 @@
> #define KVM_ITS_ITE_PINTID_SHIFT 16
> #define KVM_ITS_ITE_PINTID_MASK GENMASK_ULL(47, 16)
> #define KVM_ITS_ITE_ICID_MASK GENMASK_ULL(15, 0)
> +#define KVM_ITS_DTE_VALID_SHIFT 63
> +#define KVM_ITS_DTE_VALID_MASK BIT_ULL(63)
> +#define KVM_ITS_DTE_NEXT_SHIFT 49
> +#define KVM_ITS_DTE_NEXT_MASK GENMASK_ULL(62, 49)
> +#define KVM_ITS_DTE_ITTADDR_SHIFT 5
> +#define KVM_ITS_DTE_ITTADDR_MASK GENMASK_ULL(48, 5)
> +#define KVM_ITS_DTE_SIZE_MASK GENMASK_ULL(4, 0)
>
> static inline bool irq_is_pending(struct vgic_irq *irq)
> {
> --
> 2.5.5
>
Thanks,
-Christoffer