Re: [PATCH v3 24/25] iommu/dma: Factor out flush queue init

From: Robin Murphy
Date: Mon Aug 09 2021 - 10:47:41 EST


On 2021-08-09 13:52, Will Deacon wrote:
On Wed, Aug 04, 2021 at 06:15:52PM +0100, Robin Murphy wrote:
Factor out flush queue setup from the initial domain init so that we
can potentially trigger it from sysfs later on in a domain's lifetime.

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
Reviewed-by: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
---
drivers/iommu/dma-iommu.c | 30 ++++++++++++++++++++----------
include/linux/dma-iommu.h | 9 ++++++---
2 files changed, 26 insertions(+), 13 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 2e19505dddf9..f51b8dc99ac6 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -310,6 +310,25 @@ static bool dev_is_untrusted(struct device *dev)
return dev_is_pci(dev) && to_pci_dev(dev)->untrusted;
}
+int iommu_dma_init_fq(struct iommu_domain *domain)
+{
+ struct iommu_dma_cookie *cookie = domain->iova_cookie;
+
+ if (domain->type != IOMMU_DOMAIN_DMA_FQ)
+ return -EINVAL;
+ if (cookie->fq_domain)
+ return 0;
+
+ if (init_iova_flush_queue(&cookie->iovad, iommu_dma_flush_iotlb_all,
+ iommu_dma_entry_dtor)) {
+ pr_warn("iova flush queue initialization failed\n");
+ domain->type = IOMMU_DOMAIN_DMA;
+ return -ENODEV;

I do find this a bit odd: we assert that the caller has set domain->type
to IOMMU_DOMAIN_DMA_FQ but then on failure we reset it to IOMMU_DOMAIN_DMA
here. I think it would be less error-prone if the setting of domain->type
was handled in the same function.

On reflection I think I agree. For some reason I settled on the idea of doing this to make the callers simpler, but it turns out that unpicking it to flow logically is in fact a +4/-5 diff essentially just moving all the same statements to different places, and that's before I update comments since that theoretical race between the sysfs and DMA ops paths only exists because of sysfs having to dance around the type check here...

I'll send v4 later today or possibly tomorrow, but not in such a hurry that I skimp on the build-testing this time!

Cheers,
Robin.