linux-kernel - RE: [PATCH v5 13/29] iommufd/viommu: Introduce IOMMUFD_OBJ_HW

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Message-ID: <BN9PR11MB52767BB0CA36643D957BD2CC8C67A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Wed, 28 May 2025 08:12:41 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>
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Subject: RE: [PATCH v5 13/29] iommufd/viommu: Introduce IOMMUFD_OBJ_HW_QUEUE
 and its related struct

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Saturday, May 24, 2025 5:46 AM
> 
> On Fri, May 23, 2025 at 07:55:18AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@...dia.com>
> > > Sent: Sunday, May 18, 2025 11:22 AM
> > >
> > > +
> > > +enum iommufd_viommu_flags {
> > > +	/*
> > > +	 * The HW does not go through an address translation table but
> > > reads the
> > > +	 * physical address space directly: iommufd core should pin the
> > > physical
> > > +	 * pages backing the queue memory that's allocated for the HW
> > > QUEUE, and
> > > +	 * ensure those physical pages are contiguous in the physical space.
> > > +	 */
> > > +	IOMMUFD_VIOMMU_FLAG_HW_QUEUE_READS_PA = 1 << 0,
> > > +};
> >
> > The queue itself doesn't read an address.
> >
> > What about 'QUEUE_BASE_PA'?
> 
> But the HW queue object represents the HW feature, not the guest
> queue memory. So, it is accurate to say that it reads an address?
> 
> We have this in doc:
> - IOMMUFD_OBJ_HW_QUEUE, representing a hardware accelerated queue,
> as a subset
>   of IOMMU's virtualization features, for the IOMMU HW to directly read or
> write
>   the virtual queue memory owned by a guest OS. This HW-acceleration
> feature can
>   ...
> 

Okay. Then ACCESS_PA means both read/write?