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

[Baolu Lu]

On 2024/8/7 20:09, Jason Gunthorpe wrote:
> On Wed, Aug 07, 2024 at 02:19:57PM +0800, Baolu Lu wrote:
> > 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.
> For something debugging like that just use
>    idr_for_each_entry()
>       count++;

Yeah! It works.

> It is a weird thing to put in sysfs in the first place...

Agreed. But it has been there for years. :-)

Thanks,
baolu