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Date:   Fri, 10 Mar 2023 16:17:39 -0800
From:   Nicolin Chen <nicolinc@nvidia.com>
To:     Eric Auger <eric.auger@redhat.com>
CC:     <jgg@nvidia.com>, <robin.murphy@arm.com>, <will@kernel.org>,
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        <jean-philippe@linaro.org>, <linux-arm-kernel@lists.infradead.org>,
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Subject: Re: [PATCH v1 03/14] iommufd/device: Setup MSI on kernel-managed
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On Fri, Mar 10, 2023 at 05:45:20PM +0100, Eric Auger wrote:
> External email: Use caution opening links or attachments
> 
> 
> Hi Nicolin,
> 
> On 3/9/23 11:53, Nicolin Chen wrote:
> > The IOMMU_RESV_SW_MSI is a kernel-managed domain thing. So, it should be
> > only setup on a kernel-managed domain only. If the attaching domain is a
> > user-managed domain, redirect the hwpt to hwpt->parent to do it correctly.
> >
> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> > ---
> >  drivers/iommu/iommufd/device.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> > index f95b558f5e95..a3e7d2889164 100644
> > --- a/drivers/iommu/iommufd/device.c
> > +++ b/drivers/iommu/iommufd/device.c
> > @@ -350,7 +350,8 @@ static int iommufd_group_setup_msi(struct iommufd_group *igroup,
> >        * call iommu_get_msi_cookie() on its behalf. This is necessary to setup
> >        * the MSI window so iommu_dma_prepare_msi() can install pages into our
> >        * domain after request_irq(). If it is not done interrupts will not
> > -      * work on this domain.
> > +      * work on this domain. And the msi_cookie should be always set into the
> s/And the/The/

OK.

> > +      * kernel-managed (parent) domain.
> >        *
> >        * FIXME: This is conceptually broken for iommufd since we want to allow
> >        * userspace to change the domains, eg switch from an identity IOAS to a
> > @@ -358,6 +359,8 @@ static int iommufd_group_setup_msi(struct iommufd_group *igroup,
> >        * matches what the IRQ layer actually expects in a newly created
> >        * domain.
> >        */
> > +     if (hwpt->parent)
> > +             hwpt = hwpt->parent;
> I guess there is a garantee the parent hwpt is necessarily a
> kernel-managed domain?

Yes. It must be.

> Is it that part of the spec that enforces it?

The hwpt_alloc() function has a sanity to enforce that.

> IOMMU_HWPT_ALLOC doc says:
> " * A user-managed HWPT will be created from a given parent HWPT via
> @pt_id, in
>  * which the parent HWPT must be allocated previously via the same ioctl
> from a
>  * given IOAS.
> "
> Maybe precise that in the commit msg?

There is a paragraph just above that, for kernel-managed HWPT:

455  * A normal HWPT will be created with the mappings from the given IOAS.
456  * The @data_type for its allocation can be set to IOMMU_HWPT_TYPE_DEFAULT, or
457  * another type (being listed below) to specialize a kernel-managed HWPT.

Perhaps we could rephrase "normal HWPT" with "kernel-managed
HWPT", to make it more clear.

Thanks
Nic