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

[Christoffer Dall <cdall@linaro.org>]

On Wed, May 03, 2017 at 04:07:45PM +0200, Auger Eric wrote:
> Hi Christoffer,
> On 30/04/2017 22:55, Christoffer Dall wrote:
> > 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).
> Not sure I understand your comment.
> 
> Doc says:
>  - next: equals to 0 if this entry is the last one; otherwise it
>    corresponds to the deviceid offset to the next DTE, capped by
>    2^14 -1.
> 
> This is independent on 1 or 2 levels as we sort the devices by
> deviceid's and compute the delta between those id.

see below.

> > 
> > I have a feeling this wasn't tested with 2 level device tables.  Could
> > that be true?
> No this was tested with 1 & and 2 levels (I hacked the guest to force 2
> levels). 1 test hole I have though is all my dte's currently belong to
> the same 2d level page, ie. my deviceid are not scattered enough.
> > 
> >> +	       (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.
> yep
> > 
> >> + * @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 ?
> renamed into handle_l1_dte
> > 
> >> +{
> >> +	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) ?
> no because 1st level entries have a fixed size of GITS_LVL1_ENTRY_SIZE bytes

yes, but the ID you calculate is a result of how many IDs each 64K 2nd
level table can hold, which depends on the size of each entry in the 2nd
level table, right?  Or am I misunderstanding how this works completely.

> > 
> >> +	u64 entry = *(u64 *)addr;
> >> +	int ret, ite_esz = abi->ite_esz;
> > 
> > Should this be ite_esz or dte_esz?
> 
> you're correct. dte_esz should be used.
> > 
> >> +	gpa_t gpa;
> > 
> > nit: put declarations with initialization on separate lines.
> OK
> > 
> >> +
> >> +	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.
> added. note we exit as soon as the last element is found when scanning
> l2 tables.
> > 
> > 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.
> see above comment on next_index semantic. In the doc I talk about
> deviceid offset and not of table index.
> 

ok, I see, I was misled by the definition of lookup_table saying that it
returns 1 if the last element is identified, which is only true when you
actually find an element that is valid and where the next field is zero.
I understood it to mean if it found the last item in the table it was
scanning.  So it is implied that lookup table can be called in two
levels and the return value indicates if the element was the last from
the point of view of the highest level, not in the context the last
instance was called.

Note that it's further confusing that the handler function has the
return value the other way around, where 0 means it's the last element.
Perhaps you could make this much more readable by introducing a define
for the return values.

Thanks,
-Christoffer