On 02.11.2021 12:03, Roger Pau Monné wrote: > On Tue, Nov 02, 2021 at 11:13:08AM +0100, Jan Beulich wrote: >> On 25.10.2021 12:28, Roger Pau Monné wrote: >>> On Thu, Oct 21, 2021 at 11:59:02AM +0200, Jan Beulich wrote: >>>> The two are really meant to be independent settings; iov_supports_xt() >>>> using || instead of && was simply wrong. The corrected check is, >>>> however, redundant, just like the (correct) one in iov_detect(): These >>>> hook functions are unreachable without acpi_ivrs_init() installing the >>>> iommu_init_ops pointer, which it does only upon success. (Unlike for >>>> VT-d there is no late clearing of iommu_enable due to quirks, and any >>>> possible clearing of iommu_intremap happens only after iov_supports_xt() >>>> has run.) >>>> >>>> Signed-off-by: Jan Beulich <jbeul...@suse.com> >>>> --- >>>> In fact in iov_detect() it could be iommu_enable alone which gets >>>> checked, but this felt overly aggressive to me. Instead I'm getting the >>>> impression that the function may wrongly not get called when "iommu=off" >>>> but interrupt remapping is in use: We'd not get the interrupt handler >>>> installed, and hence interrupt remapping related events would never get >>>> reported. (Same on VT-d, FTAOD.) >>> >>> I've spend a non-trivial amount of time looking into this before >>> reading this note. AFAICT you could set iommu=off and still get x2APIC >>> enabled and relying on interrupt remapping. >> >> Right, contrary to ... >> >>>> For iov_supports_xt() the question is whether, like VT-d's >>>> intel_iommu_supports_eim(), it shouldn't rather check iommu_intremap >>>> alone (in which case it would need to remain a check rather than getting >>>> converted to ASSERT()). >>> >>> Hm, no, I don't think so. I think iommu_enable should take precedence >>> over iommu_intremap, and having iommu_enable == false should force >>> interrupt remapping to be reported as disabled. Note that disabling it >>> in iommu_setup is too late, as the APIC initialization will have >>> already taken place. >>> >>> It's my reading of the command line parameter documentation that >>> setting iommu=off should disable all usage of the IOMMU, and that >>> includes the interrupt remapping support (ie: a user should not need >>> to set iommu=off,no-intremap) >> >> ... that documentation. But I think it's the documentation that >> wants fixing, such that iommu=off really only control DMA remap. > > IMO I think it's confusing to have sub-options that could be enabled > when you set the global one to off. I would expect `iommu=off` to > disable all the iommu related options, and I think it's fair for > people to expect that behavior.
It occurs to me that this reply of yours here contradicts your R-b on patch 1, in particular with its revision log saying: v2: Treat iommu_enable and iommu_intremap as separate options. Even in case I receive a release ack from Ian, I'll try to remember to hold off committing that until this apparent (to me) confusion was sorted. Jan
