Messages in this thread | | | Date | Tue, 18 Sep 2018 18:10:13 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v7 4/6] iommu: Add bootup option "iommu.non_strict" |
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On Fri, Sep 14, 2018 at 03:30:22PM +0100, Robin Murphy wrote: > From: Zhen Lei <thunder.leizhen@huawei.com> > > Add a bootup option to make the system manager can choose which mode to > be used. The default mode is strict. > > Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> > [rm: move handling out of SMMUv3 driver] > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > .../admin-guide/kernel-parameters.txt | 13 ++++++++++ > drivers/iommu/iommu.c | 26 +++++++++++++++++++ > 2 files changed, 39 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 9871e649ffef..406b91759b62 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -1749,6 +1749,19 @@ > nobypass [PPC/POWERNV] > Disable IOMMU bypass, using IOMMU for PCI devices. > > + iommu.non_strict= [ARM64] > + Format: { "0" | "1" } > + 0 - strict mode, default. > + Release IOVAs after the related TLBs are invalid > + completely. > + 1 - non-strict mode. > + Put off TLBs invalidation and release memory first. > + It's good for scatter-gather performance but lacks > + full isolation, an untrusted device can access the > + reused memory because the TLBs may still valid. > + Please take full consideration before choosing this > + mode. Note that, VFIO will always use strict mode.
This text needs help. How about something like:
0 - strict mode, default. Invalidate the TLB of the IOMMU hardware as part of every unmap() operation. 1 - lazy mode. Defer TLB invalidation so that the TLB of the IOMMU hardware is invalidated periodically, rather than as part of every unmap() operation.
(generally, I think I'd s/non strict/lazy/ in this patch to avoid the double negatives)
> + > iommu.passthrough= > [ARM64] Configure DMA to bypass the IOMMU by default. > Format: { "0" | "1" } > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 8c15c5980299..2cabd0c0a4f3 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -41,6 +41,7 @@ static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_IDENTITY; > #else > static unsigned int iommu_def_domain_type = IOMMU_DOMAIN_DMA; > #endif > +static bool iommu_dma_non_strict __read_mostly; > > struct iommu_callback_data { > const struct iommu_ops *ops; > @@ -131,6 +132,24 @@ static int __init iommu_set_def_domain_type(char *str) > } > early_param("iommu.passthrough", iommu_set_def_domain_type); > > +static int __init iommu_dma_setup(char *str) > +{ > + int ret; > + > + ret = kstrtobool(str, &iommu_dma_non_strict); > + if (ret) > + return ret; > + > + if (iommu_dma_non_strict) { > + pr_warn("WARNING: iommu non-strict mode is chosen.\n" > + "It's good for scatter-gather performance but lacks full isolation\n");
Hmm, not sure about this message either and tainting is probably over the top. Maybe drop the taint and just pr_info something like "IOMMU DMA ops using lazy TLB invalidation: unable to protect against malicious devices"
> + add_taint(TAINT_WARN, LOCKDEP_STILL_OK); > + } > + > + return 0; > +} > +early_param("iommu.non_strict", iommu_dma_setup); > + > static ssize_t iommu_group_attr_show(struct kobject *kobj, > struct attribute *__attr, char *buf) > { > @@ -1072,6 +1091,13 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev) > group->default_domain = dom; > if (!group->domain) > group->domain = dom; > + > + if (dom && iommu_dma_non_strict) { > + int attr = 1; > + iommu_domain_set_attr(dom, > + DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE, > + &attr); > + }
Hmm, I don't think we can guarantee that we're working with the DMA domain here. Does this all fall out in the wash for the identity domain?
Will
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