On Wed, Sep 14, 2022 at 04:51:16PM -0700, Jacob Pan wrote: > Hi Kirill, > > On Wed, 14 Sep 2022 18:45:32 +0300, "Kirill A. Shutemov" > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > > On Wed, Sep 14, 2022 at 08:31:56AM -0700, Ashok Raj wrote: > > > On Wed, Sep 14, 2022 at 06:18:18PM +0300, Kirill A. Shutemov wrote: > > > > > > > > > > > > > > > > The patch below implements something like this. It is PoC, > > > > > > > > build-tested only. > > > > > > > > > > > > > > > > To be honest, I hate it. It is clearly a layering violation. > > > > > > > > It feels dirty. But I don't see any better way as we tie > > > > > > > > orthogonal features together. > > > > > > > > > > > > > > > > Also I have no idea how to make forced PASID allocation if > > > > > > > > LAM enabled. What the API has to look like? > > > > > > > > > > > > > > Jacob, Ashok, any comment on this part? > > > > > > > > > > > > > > I expect in many cases LAM will be enabled very early (like > > > > > > > before malloc is functinal) in process start and it makes PASID > > > > > > > allocation always fail. > > > > > > > > > > > > > > Any way out? > > > > > > > > > > > > We need closure on this to proceed. Any clue? > > > > > > > > > > Failing PASID allocation seems like the right thing to do here. If > > > > > the application is explicitly allocating PASID's it can opt-out > > > > > using the similar mechanism you have for LAM enabling. So user takes > > > > > responsibility for sanitizing pointers. > > > > > > > > > > If some library is using an accelerator without application > > > > > knowledge, that would use the failure as a mechanism to use an > > > > > alternate path if one exists. > > > > > > > > > > I don't know if both LAM and SVM need a separate forced opt-in (or i > > > > > don't have an opinion rather). Is this what you were asking? > > > > > > > > > > + Joerg, JasonG in case they have an opinion. > > > > > > > > My point is that the patch provides a way to override LAM vs. PASID > > > > mutual exclusion, but only if PASID allocated first. If we enabled > > > > LAM before PASID is allcoated there's no way to forcefully allocate > > > > PASID, bypassing LAM check. I think there should be one, no? > > > > > > Yes, we should have one for force enabling SVM too if the application > > > asks for forgiveness. > > > > What is the right API here? > > > It seems very difficult to implement a UAPI for the applications to > override at a runtime. Currently, SVM bind is under the control of > individual drivers. It could be at the time of open or some ioctl. > > Perhaps, this can be a platform policy via some commandline option. e.g. > intel_iommu=sva_lam_coexist. I think it has to be per-process, not a system-wide handle. Maybe a separate arch_prctl() to allow to enable LAM/SVM coexisting? It would cover both sides of the API, relaxing check for both. -- Kiryl Shutsemau / Kirill A. Shutemov
