Re: [PATCH v3 18/19] KVM: arm64: ITS: Device table save/restore

[Auger Eric <eric.auger@redhat.com>]

Hi Andre,

On 24/03/2017 11:38, Auger Eric wrote:
> Hi Andre,
> 
> On 22/03/2017 15:39, Andre Przywara wrote:
>> Hi,
>>
>> On 06/03/17 11:34, Eric Auger wrote:
>>> This patch flushes 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 flush
>>> the translation table using the vgic_its_flush/restore_itt
>>> routines.
>>>
>>> On restore, devices are re-allocated and their itte are
>>> re-built.
>>
>> Some minor things below.
>> In general I had quite some trouble to understand what's going on here,
>> though I convinced myself that this is correct. So could you add a bit
>> more comments here? For instance to explain that we have to explicitly
>> handle the L1 table on restore, but not on flush.
> 
> On flush vgic_its_check_id does the 2 stage handling and computes the
> entry address from the devid:
> 
> 		if (!vgic_its_check_id(its, baser,
> 				       dev->device_id, &eaddr))
> 
> Then you simply flush the entry at that address
> 
> On restore, you need to scan the level1 and level2 tables for valid entries.
>>
>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>>
>>> ---
>>> 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 | 144 ++++++++++++++++++++++++++++++++++++++++++-
>>>  1 file changed, 142 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>>> index a216849..27ebabd 100644
>>> --- a/virt/kvm/arm/vgic/vgic-its.c
>>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>>> @@ -1849,12 +1849,137 @@ static int vgic_its_restore_itt(struct vgic_its *its,
>>>  }
>>>  
>>>  /**
>>> + * vgic_its_flush_dte - Flush a device table entry at a given GPA
>>> + *
>>> + * @its: ITS handle
>>> + * @dev: ITS device
>>> + * @ptr: GPA
>>> + */
>>> +static int vgic_its_flush_dte(struct vgic_its *its,
>>> +			      struct its_device *dev, gpa_t ptr)
>>> +{
>>> +	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 = (((u64)next_offset << 45) | (itt_addr_field << 5) |
>>
>> So this gives you 19 bits for next_offset, but the value of
>> VITS_DTE_MAX_DEVID_OFFSET suggests 20 bits. It should become more
>> obvious what's happening here if use "BITS(x) - 1" at the definition as
>> suggested before.
> Yes this should be 19 bits
>>
>> Also you limit itt_addr here to 40 bits, where the actual limit seems to
>> be 44 bits (52 - 8). Is that limited by KVM somewhere else?
> 
> Those 40 bits match [47:8] of the itt_addr. I limited to 48 since I
> found a comment saying
> /*
>  * We only implement 48 bits of PA at the moment, although the ITS
>  * supports more. Let's be restrictive here.
>  */
> 
> 
> On the other hand there is
> #define its_cmd_get_ittaddr(cmd) its_cmd_mask_field(cmd, 2,  8, 44)
> To me this is wrong. I would have expected its_cmd_mask_field(cmd, 2,
> 8, 47) instead as the other *_ADDRESS()
Forget that. That's my own code which is wrong!

Cheers

Eric
> 
> If confirmed I will send a fix.
> 
> 
> 
>> Even if it is, I think we should make sure that itt_addr_field doesn't
>> spill over into next_offset.
>>
>>> +		(dev->nb_eventid_bits - 1));
>>
>> Mmmh, here nb_eventid_bits seems to be the real bit number again. Puzzled.
> corrected
>>
>>> +	val = cpu_to_le64(val);
>>> +	ret = kvm_write_guest(kvm, ptr, &val, 8);
>>> +	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;
>>> +	size_t size;
>>> +	u64 val, *p = (u64 *)ptr;
>>> +	int ret;
>>> +
>>> +	val = *p;
>>> +	val = le64_to_cpu(val);
>>> +
>>> +	size = val & GENMASK_ULL(4, 0);
>>> +	itt_addr = (val & GENMASK_ULL(44, 5)) >> 5;
>>> +	*next = 1;
>>> +
>>> +	if (!itt_addr)
>>> +		return 0;
>>> +
>>> +	/* dte entry is valid */
>>> +	*next = (val & GENMASK_ULL(63, 45)) >> 45;
>>
>> No need for GENMASK, just shift by 45.
> yes
>>
>>> +
>>> +	ret = vgic_its_alloc_device(its, &dev, id,
>>> +				    itt_addr, size);
>>> +	if (ret)
>>> +		return ret;
>>> +	ret = vgic_its_restore_itt(its, dev);
>>> +
>>> +	return ret;
>>> +}
>>> +
>>> +/**
>>>   * vgic_its_flush_device_tables - flush the device table and all ITT
>>>   * into guest RAM
>>>   */
>>>  static int vgic_its_flush_device_tables(struct vgic_its *its)
>>>  {
>>> -	return -ENXIO;
>>> +	struct its_device *dev;
>>> +	u64 baser;
>>> +
>>> +	baser = its->baser_device_table;
>>> +
>>> +	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_flush_itt(its, dev);
>>> +		if (ret)
>>> +			return ret;
>>> +
>>> +		ret = vgic_its_flush_dte(its, dev, eaddr);
>>> +		if (ret)
>>> +			return ret;
>>> +		}
>>
>> whitespace ?
> OK
>>
>>> +	return 0;
>>> +}
>>> +
>>> +/**
>>> + * handle_l1_entry - callback used for L1 entries (2 stage case)
>>> + *
>>> + * @its: its handle
>>> + * @id: id
>>> + * @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)
>>> +{
>>> +	u64 *pe = addr;
>>> +	gpa_t gpa;
>>> +	int l2_start_id = id * (SZ_64K / 8);
>>
>> I think we can use GITS_LVL1_ENTRY_SIZE here, which I suppose is what
>> the 8 stands for.
> yes
>>
>>> +	int ret;
>>> +
>>> +	*pe = le64_to_cpu(*pe);
>>
>> Is it correct to _update_ the entry here? I think that breaks BE, right?
>> Beside I believe the ITS is not supposed to tinker with the L1 table
>> entries, isn't it?
>>
>> So should it be instead:
>> 	u64 pe = *(u64 *)addr;
>> 	
>> 	pe = le64_to_cpu(pe);
>>
>> instead?
>> And what "pe" stand for anyway? Maybe "entry" instead?
> correct. I fixed that.
>>
>>> +	*next_offset = 1;
>>> +
>>> +	if (!(*pe & BIT_ULL(63)))
>>> +		return 0;
>>> +
>>> +	gpa = *pe & GENMASK_ULL(51, 16);
>>> +
>>> +	ret = lookup_table(its, gpa, SZ_64K, 8,
>>> +			    l2_start_id, vgic_its_restore_dte, NULL);
>>> +
>>> +	if (ret == 1) {
>>> +		/* last entry was found in this L2 table */
>>> +		*next_offset = 0;
>>> +		ret = 0;
>>> +	}
>>> +
>>> +	return ret;
>>>  }
>>>  
>>>  /**
>>> @@ -1863,7 +1988,22 @@ static int vgic_its_flush_device_tables(struct vgic_its *its)
>>>   */
>>>  static int vgic_its_restore_device_tables(struct vgic_its *its)
>>>  {
>>> -	return -ENXIO;
>>> +	u64 baser = its->baser_device_table;
>>> +	int l1_tbl_size = GITS_BASER_NR_PAGES(baser) * SZ_64K;
>>> +	int l1_esz = GITS_BASER_ENTRY_SIZE(baser);
>>> +	gpa_t l1_gpa;
>>> +
>>> +	l1_gpa = BASER_ADDRESS(baser);
>>> +	if (!l1_gpa)
>>> +		return 0;
>>> +
>>> +	if (!(baser & GITS_BASER_INDIRECT))
>>> +		return lookup_table(its, l1_gpa, l1_tbl_size, l1_esz,
>>> +				    0, vgic_its_restore_dte, NULL);
>>> +
>>> +	/* two stage table */
>>> +	return lookup_table(its, l1_gpa, l1_tbl_size, 8, 0,
>>> +			    handle_l1_entry, NULL);
>>
>> That usage of lookup_table with the callback is pretty neat!
> thanks a lot for your time and the numerous bugs you found!
> 
> Cheers
> 
> Eric
>>
>> Cheers,
>> Andre.
>>
>>>  }
>>>  
>>>  static int vgic_its_flush_cte(struct vgic_its *its,
>>>
>>
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