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

From: Baolu Lu
Date: Wed Aug 07 2024 - 02:20:12 EST


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@xxxxxxxxxxxxxxx>
---
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