linux-kernel - Re: [PATCH v3 16/23] Documentation: userspace-api: iommufd: Update vQUEUE

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Message-ID: <aBR0wWzQablOklyW@archie.me>
Date: Fri, 2 May 2025 14:31:13 +0700
From: Bagas Sanjaya <bagasdotme@...il.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, kevin.tian@...el.com, corbet@....net, will@...nel.org,
	robin.murphy@....com, joro@...tes.org, thierry.reding@...il.com,
	vdumpa@...dia.com, jonathanh@...dia.com, shuah@...nel.org,
	jsnitsel@...hat.com, nathan@...nel.org, peterz@...radead.org,
	yi.l.liu@...el.com, mshavit@...gle.com, praan@...gle.com,
	zhangzekun11@...wei.com, iommu@...ts.linux.dev,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kselftest@...r.kernel.org, patches@...ts.linux.dev,
	mochs@...dia.com, alok.a.tiwari@...cle.com, vasant.hegde@....com
Subject: Re: [PATCH v3 16/23] Documentation: userspace-api: iommufd: Update
 vQUEUE

On Thu, May 01, 2025 at 10:29:58PM -0700, Nicolin Chen wrote:
> On Fri, May 02, 2025 at 10:50:07AM +0700, Bagas Sanjaya wrote:
> > On Thu, May 01, 2025 at 04:01:22PM -0700, Nicolin Chen wrote:
> > > +- IOMMUFD_OBJ_VQUEUE, representing a hardware accelerated virtual 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
> > > +  allows VM to work with the IOMMU HW directly without a VM Exit, i.e. reducing
> > > +  overhead from the hypercalls. Along with this vQUEUE object, iommufd provides
> > > +  user space an mmap interface for VMM to mmap a physical MMIO region from the
> > > +  host physical address space to the guest physical address space, allowing the
> > > +  guest OS to control the allocated vQUEUE HW. Thus, when allocating a vQUEUE,
> > > +  the VMM must request a pair of VMA info (vm_pgoff/size) for an mmap syscall.
> > > +  The length argument of an mmap syscall can be smaller than the given size for
> > > +  a partial mmap, but the addr argument of the mmap syscall should never offset
> > > +  from the returned vm_pgoff, which implies that an mmap will always start from
> > 
> > Did you mean never be offset from returned vm_pgoff?
> 
> Yes. Will fix this.
> 
> > > +  the beginning of the physical MMIO region.
> > > +
> > 
> > Confused...
> 
> Meaning that VMM should just use the given vm_pgoff as is, without
> adding any offset to the vm_pgoff.

Understood, thanks!
 
-- 
An old man doll... just what I always wanted! - Clara

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