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

[Baolu Lu]

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