On 03.11.2021 16:06, Roger Pau Monné wrote: > On Wed, Nov 03, 2021 at 10:46:40AM +0100, Jan Beulich wrote: >> 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. > > Right, I see. patch 1 uses > > if ( !iommu_enable && !iommu_intremap ) > return; > > Which I think should be: > > if ( !iommu_enable ) > return; > > Sorry I didn't realize in that context. I think we need to decide > whether we want to fix the documentation to match the code, or whether > we should fix the code to match the documentation.
Except that adjusting the conditional(s) in patch 1 would then be a functional change that's not really the purpose of that patch - it really only folds acpi_ivrs_init()'s and acpi_parse_dmar()'s into a vendor-independent instance in acpi_iommu_init(). Alternatively we could adjust the conditional here (in patch 3), but that would feel unrelated once again, as this change is supposed to be AMD-specific. > My preference would be for the latter, because I think the resulting > interface would be clearer. That will require introducing a new > dmaremap iommu suboption, but again I think this will result in a > better interface overall. I guess we could do with a 3rd opinion: Paul, any chance? In any event I hope that we can agree that patches 1 and 2 are okay for 4.16 in their present shape, and patch 3 (plus whichever further ones) would better wait for post-4.16? Jan
