Messages in this thread | | | Date | Wed, 15 Feb 2023 15:28:23 +0800 | Subject | Re: [PATCH 2/4] iommu: Use group ownership to avoid driver attachment | From | Baolu Lu <> |
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On 2023/2/15 14:56, Tian, Kevin wrote: >> From: Baolu Lu<baolu.lu@linux.intel.com> >> Sent: Wednesday, February 15, 2023 1:51 PM >> >> On 2/13/23 10:19 PM, Jason Gunthorpe wrote: >>> On Mon, Feb 13, 2023 at 03:49:39PM +0800, Lu Baolu wrote: >>>> @@ -2992,6 +2987,14 @@ static ssize_t iommu_group_store_type(struct >> iommu_group *group, >>>> else >>>> return -EINVAL; >>>> >>>> + if (req_type != IOMMU_DOMAIN_DMA_FQ || >>>> + group->default_domain->type != IOMMU_DOMAIN_DMA) { >>>> + ret = iommu_group_claim_dma_owner(group, (void *)buf); >>>> + if (ret) >>>> + return ret; >>>> + group_owner_claimed = true; >>>> + } >>> I don't get it, this should be done unconditionally. If we couldn't >>> take ownership then we simply can't progress. >> The existing code allows the user to switch the default domain from >> strict to lazy invalidation mode. The default domain is not changed, >> hence it should be seamless and transparent to the device driver. > Is there real usage relying on this transition for a bound device? > > In concept strict->lazy transition implies relaxed DMA security. It's hard > to think of a motivation of doing so while the device might be doing > in-fly DMAs. > > Presumably such perf/security tradeoff should be planned way before > binding device/driver together. > > btw if strict->lazy is allowed why lazy->strict is prohibited? >
We all know, strict vs. lazy is a tradeoff between performance and security.
strict -> lazy: driver works in secure mode. This transition trades off security for better performance.
lazy->strict: The driver is already working in non-safety mode. This transition only results in worse performance. It makes no sense. If user want to put the driver in a secure mode, they need to unbind the driver, reset the device and do the lazy->strict transition.
Robin might have better insights.
Best regards, baolu
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