Re: [PATCH v3 4/6] iommu: Move IOMMU pagesize check to attach_device

Lu Baolu
2021-10-20T05:21:54Z

On 2021/10/20 0:37, Sven Peter via iommu wrote:
> The iova allocator is capable of handling any granularity which is a power
> of two. Remove the much stronger condition that the granularity must be
> smaller or equal to the CPU page size from a BUG_ON there.
> Instead, check this condition during __iommu_attach_device and fail
> gracefully.
>
> Signed-off-by: Sven Peter<sven@svenpeter.dev>
> ---
> drivers/iommu/iommu.c | 35 ++++++++++++++++++++++++++++++++---
> drivers/iommu/iova.c | 7 ++++---
> include/linux/iommu.h | 5 +++++
> 3 files changed, 41 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index dd7863e453a5..28896739964b 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -80,6 +80,8 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
> unsigned type);
> static int __iommu_attach_device(struct iommu_domain *domain,
> struct device *dev);
> +static void __iommu_detach_device(struct iommu_domain *domain,
> + struct device *dev);
> static int __iommu_attach_group(struct iommu_domain *domain,
> struct iommu_group *group);
> static void __iommu_detach_group(struct iommu_domain *domain,
> @@ -1974,6 +1976,19 @@ void iommu_domain_free(struct iommu_domain *domain)
> }
> EXPORT_SYMBOL_GPL(iommu_domain_free);
>
> +static int iommu_check_page_size(struct iommu_domain *domain)
> +{
> + if (!iommu_is_paging_domain(domain))
> + return 0;
> +
> + if (!(domain->pgsize_bitmap & (PAGE_SIZE | (PAGE_SIZE - 1)))) {
> + pr_warn("IOMMU pages cannot exactly represent CPU pages.\n");
> + return -EFAULT;
> + }
> +
> + return 0;
> +}
> +
> static int __iommu_attach_device(struct iommu_domain *domain,
> struct device *dev)
> {
> @@ -1983,9 +1998,23 @@ static int __iommu_attach_device(struct iommu_domain *domain,
> return -ENODEV;
>
> ret = domain->ops->attach_dev(domain, dev);
> - if (!ret)
> - trace_attach_device_to_domain(dev);
> - return ret;
> + if (ret)
> + return ret;
> +
> + /*
> + * Check that CPU pages can be represented by the IOVA granularity.
> + * This has to be done after ops->attach_dev since many IOMMU drivers
> + * only limit domain->pgsize_bitmap after having attached the first
> + * device.
> + */
> + ret = iommu_check_page_size(domain);
> + if (ret) {
> + __iommu_detach_device(domain, dev);
> + return ret;
> + }

It looks odd. __iommu_attach_device() attaches an I/O page table for a
device. How does it relate to CPU pages? Why is it a failure case if CPU
page size is not covered?

Best regards,
baolu