Re: [PATCH v3 3/7] iommu/vt-d: Always reserve a domain ID for identity setup

Baolu Lu
2024-08-07T06:20:01Z

On 2024/8/7 1:06, Jason Gunthorpe wrote:
> On Tue, Aug 06, 2024 at 10:39:37AM +0800, Lu Baolu wrote:
>> We will use a global static identity domain. Reserve a static domain ID
>> for it.
>>
>> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>
>> ---
>> drivers/iommu/intel/iommu.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index 723ea9f3f501..c019fb3b3e78 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -1440,10 +1440,10 @@ static int iommu_init_domains(struct intel_iommu *iommu)
>> * entry for first-level or pass-through translation modes should
>> * be programmed with a domain id different from those used for
>> * second-level or nested translation. We reserve a domain id for
>> - * this purpose.
>> + * this purpose. This domain id is also used for identity domain
>> + * in legacy mode.
>> */
>> - if (sm_supported(iommu))
>> - set_bit(FLPT_DEFAULT_DID, iommu->domain_ids);
>> + set_bit(FLPT_DEFAULT_DID, iommu->domain_ids);
> That should probablyturn into an IDA someday, it would likely be more
> memory efficient than bitmap_zalloc()

I have tried to. But I failed to find a suitable ida interface to
calculate the count of allocated domain IDs to replace bitmap_weight()
in below code.

static ssize_t domains_used_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct intel_iommu *iommu = dev_to_intel_iommu(dev);
return sysfs_emit(buf, "%d\n",
bitmap_weight(iommu->domain_ids,
cap_ndoms(iommu->cap)));
}
static DEVICE_ATTR_RO(domains_used);

Thanks,
baolu