Re: [PATCH 0/5] Share sva domains with all devices bound to a mm

[Tina Zhang]

Hi,

On 8/10/23 15:49, Tian, Kevin wrote:
> > From: Zhang, Tina <tina.zhang@xxxxxxxxx>
> > Sent: Thursday, August 10, 2023 9:32 AM
> >
> > Hi,
> >
> > On 8/9/23 17:41, Tian, Kevin wrote:
> > > > From: Zhang, Tina <tina.zhang@xxxxxxxxx>
> > > > Sent: Tuesday, August 8, 2023 3:50 PM
> > > >
> > > > A sva domain's lifetime begins with binding a device to a mm and ends
> > > > by releasing all the bound devices from that sva domain. Technically,
> > > > there could be more than one sva domain identified by the mm PASID for
> > > > the use of bound devices issuing DMA transactions.
> > >
> > > Could you elaborate it with some concrete examples which motivate
> > > this change?
> > The motivation is to remove the superfluous IOTLB invalidation in
> > current VT-d driver.
> >
> > Currently, in VT-d driver, due to lacking shared sva domain info, in
> > intel_flush_svm_range(), both iotlb and dev-tlb invalidation operations
> > are performed per-device. However, difference devices could be behind
> > one IOMMU (e.g., four devices are behind one IOMMU) and invoking iotlb
> > per-device gives us more iotlb invalidation than necessary (4 iotlb
> > invalidation instead of 1). This issue may give more performance impact
> > when in a virtual machine guest, as currently we have one virtual VT-d
> > for in front of those virtual devices.
> >
> >
> > This patch fixes this issue by attaching shared sva domain information
> > to mm, so that it can be utilized in the mm_notifier_ops callbacks.
>
> that is one of the motivations. e.g. another one as Jason suggested
> is to cleanup to decouple the common sva logic from enqcmd. Both
> should be mentioned in next version cover letter.
Right.

Regards,
-Tina