linux-kernel - Re: [PATCH v1 03/14] iommufd/device: Setup MSI on kernel-managed domains

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Message-ID: <919e32d5-26ef-7327-e25f-565967c94e6a@redhat.com>
Date:   Fri, 10 Mar 2023 17:45:20 +0100
From:   Eric Auger <eric.auger@...hat.com>
To:     Nicolin Chen <nicolinc@...dia.com>, jgg@...dia.com,
        robin.murphy@....com, will@...nel.org
Cc:     kevin.tian@...el.com, baolu.lu@...ux.intel.com, joro@...tes.org,
        shameerali.kolothum.thodi@...wei.com, jean-philippe@...aro.org,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 03/14] iommufd/device: Setup MSI on kernel-managed
 domains

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@...dia.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/
> +	 * 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?
Is it that part of the spec that enforces it?
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?

Thanks

Eric
>  	if (sw_msi_start != PHYS_ADDR_MAX && !hwpt->msi_cookie) {
>  		rc = iommu_get_msi_cookie(hwpt->domain, sw_msi_start);
>  		if (rc)