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

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Message-ID: <20240807120913.GC8473@ziepe.ca>
Date: Wed, 7 Aug 2024 09:09:13 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>,
	Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/7] iommu/vt-d: Always reserve a domain ID for
 identity setup

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@...ux.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.

For something debugging like that just use 
  idr_for_each_entry()
     count++;

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

Jason