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Message-ID: <5d0d6665-93e4-f61f-d700-008c0fcb4a2f@arm.com>
Date: Mon, 19 Jun 2023 14:33:18 +0100
From: Robin Murphy <robin.murphy@....com>
To: Lu Baolu <baolu.lu@...ux.intel.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Kevin Tian <kevin.tian@...el.com>,
Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
Alex Williamson <alex.williamson@...hat.com>,
Nicolin Chen <nicolinc@...dia.com>
Cc: iommu@...ts.linux.dev, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH 1/2] iommu: Prevent RESV_DIRECT devices from blocking
domains
On 07/06/2023 4:51 am, Lu Baolu wrote:
> The IOMMU_RESV_DIRECT flag indicates that a memory region must be mapped
> 1:1 at all times. This means that the region must always be accessible to
> the device, even if the device is attached to a blocking domain. This is
> equal to saying that IOMMU_RESV_DIRECT flag prevents devices from being
> attached to blocking domains.
>
> This also implies that devices that implement RESV_DIRECT regions will be
> prevented from being assigned to user space since taking the DMA ownership
> immediately switches to a blocking domain.
>
> The rule of preventing devices with the IOMMU_RESV_DIRECT regions from
> being assigned to user space has existed in the Intel IOMMU driver for
> a long time. Now, this rule is being lifted up to a general core rule,
> as other architectures like AMD and ARM also have RMRR-like reserved
> regions. This has been discussed in the community mailing list and refer
> to below link for more details.
>
> Other places using unmanaged domains for kernel DMA must follow the
> iommu_get_resv_regions() and setup IOMMU_RESV_DIRECT - we do not restrict
> them in the core code.
>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Alex Williamson <alex.williamson@...hat.com>
> Cc: Kevin Tian <kevin.tian@...el.com>
> Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> Link: https://lore.kernel.org/linux-iommu/BN9PR11MB5276E84229B5BD952D78E9598C639@BN9PR11MB5276.namprd11.prod.outlook.com
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
> include/linux/iommu.h | 2 ++
> drivers/iommu/iommu.c | 39 +++++++++++++++++++++++++++++----------
> 2 files changed, 31 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index d31642596675..fd18019ac951 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -409,6 +409,7 @@ struct iommu_fault_param {
> * @priv: IOMMU Driver private data
> * @max_pasids: number of PASIDs this device can consume
> * @attach_deferred: the dma domain attachment is deferred
> + * @requires_direct: The driver requested IOMMU_RESV_DIRECT
> *
> * TODO: migrate other per device data pointers under iommu_dev_data, e.g.
> * struct iommu_group *iommu_group;
> @@ -422,6 +423,7 @@ struct dev_iommu {
> void *priv;
> u32 max_pasids;
> u32 attach_deferred:1;
> + u32 requires_direct:1;
> };
>
> int iommu_device_register(struct iommu_device *iommu,
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 9e0228ef612b..e59de7852067 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -959,12 +959,7 @@ static int iommu_create_device_direct_mappings(struct iommu_domain *domain,
> unsigned long pg_size;
> int ret = 0;
>
> - if (!iommu_is_dma_domain(domain))
> - return 0;
> -
> - BUG_ON(!domain->pgsize_bitmap);
> -
> - pg_size = 1UL << __ffs(domain->pgsize_bitmap);
> + pg_size = domain->pgsize_bitmap ? 1UL << __ffs(domain->pgsize_bitmap) : 0;
> INIT_LIST_HEAD(&mappings);
>
> iommu_get_resv_regions(dev, &mappings);
> @@ -974,13 +969,22 @@ static int iommu_create_device_direct_mappings(struct iommu_domain *domain,
> dma_addr_t start, end, addr;
> size_t map_size = 0;
>
> + if (entry->type == IOMMU_RESV_DIRECT)
> + dev->iommu->requires_direct = 1;
> +
> + if ((entry->type != IOMMU_RESV_DIRECT &&
> + entry->type != IOMMU_RESV_DIRECT_RELAXABLE) ||
> + !iommu_is_dma_domain(domain))
> + continue;
> +
> + if (WARN_ON_ONCE(!pg_size)) {
> + ret = -EINVAL;
> + goto out;
> + }
> +
> start = ALIGN(entry->start, pg_size);
> end = ALIGN(entry->start + entry->length, pg_size);
>
> - if (entry->type != IOMMU_RESV_DIRECT &&
> - entry->type != IOMMU_RESV_DIRECT_RELAXABLE)
> - continue;
> -
> for (addr = start; addr <= end; addr += pg_size) {
> phys_addr_t phys_addr;
>
> @@ -2121,6 +2125,21 @@ static int __iommu_device_set_domain(struct iommu_group *group,
> {
> int ret;
>
> + /*
> + * If the driver has requested IOMMU_RESV_DIRECT then we cannot allow
> + * the blocking domain to be attached as it does not contain the
> + * required 1:1 mapping. This test effectively exclusive the device from
> + * being used with iommu_group_claim_dma_owner() which will block vfio
> + * and iommufd as well.
> + */
> + if (dev->iommu->requires_direct &&
> + (new_domain->type == IOMMU_DOMAIN_BLOCKED ||
Given the notion elsewhere that we want to use the blocking domain as a
last resort to handle an attach failure, at face value it looks suspect
that failing to attach to a blocking domain could also be a thing. I
guess technically this is failing at a slightly different level so maybe
it does work out OK, but it's still smelly.
The main thing, though, is that not everything implements the
IOMMU_DOMAIN_BLOCKED optimisation, so a nominal blocking domain could be
IOMMU_DOMAIN_UNMANAGED as well. FWIW I'd prefer to make the RESV_DIRECT
check explicit in __iommu_take_dma_ownership() rather than hide it in an
implementation detail; that's going to be a lot clearer to reason about
as time goes on.
Thanks,
Robin.
> + new_domain == group->blocking_domain)) {
> + dev_warn(dev,
> + "Firmware has requested this device have a 1:1 IOMMU mapping, rejecting configuring the device without a 1:1 mapping. Contact your platform vendor.\n");
> + return -EINVAL;
> + }
> +
> if (dev->iommu->attach_deferred) {
> if (new_domain == group->default_domain)
> return 0;
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