[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v02 1/7] arm: introduce remoteprocessor iommu module
Hi Ian, Sorry for late reply, On Wed, Jul 16, 2014 at 6:19 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote: > On Fri, 2014-07-04 at 14:59 +0100, Stefano Stabellini wrote: >> On Thu, 26 Jun 2014, Andrii Tseglytskyi wrote: >> > This is a fisrst patch from patch series which was >> > developed to handle remote (external) processors >> > memory management units. Remote processors are >> > typically used for graphic rendering (GPUs) and >> > high quality video decoding (IPUs). They are typically >> > installed on such multimedia SoCs as OMAP4 / OMAP5. >> > >> > As soon as remoteprocessor MMU typically works with >> > pagetables filled by physical addresses, which are >> > allocated by domU kernel, it is almost impossible to >> > use them under Xen, intermediate physical addresses >> > allocated by kernel, need to be translated to machine >> > addresses. >> > >> > This patch introduces a simple framework to perform >> > pfn -> mfn translation for external MMUs. >> > It introduces basic data structures and algorithms >> > needed for translation. >> > >> > Typically, when MMU is configured, some it registers >> > are updated by new values. Introduced frameworks >> > uses traps as starting point of remoteproc MMUs >> > pagetables translation. >> > >> > Change-Id: Ia4d311a40289df46a003f5ae8706c150bee1885d >> > Signed-off-by: Andrii Tseglytskyi <andrii.tseglytskyi@xxxxxxxxxxxxxxx> >> >> There is one problem with this patch: you need to find a way to "pin" >> the p2m entries for the pfns and mfns found in the pagetables translated >> by remoteproc_iommu.c. Otherwise Xen might decide to change the pfn to >> mfn mappings for the domain, breaking the pagetables already translated >> by remoteproc_iommu.c. pfn to mfn mappings are not guaranteed to be >> stable. At the moment Xen on ARM wouldn't change pfn to mfn mappings >> under the guest feet, but features like memory sharing or swapping, >> supported on x86, could cause it to happen. > > I've not fully grokked this patch but wouldn't it be easier and better > to have a hook to cause the remoteproc to throw away and rebuild its > mappings when this happens? It could be called from e.g. the TLB flush > associated with the p2m changing, I think. > Yes., you are right. And this series contains a hypercall definition, which is designed to do this. But let me explained a bit: Pagetables are translated in 2 cases: - specific register access - direct hypercall Specific register access trap was designed to hide pagetables translation completely. Kernel won't know anything that addresses were changed. And this works fine for 1 of OMAP remoteprocs - IPU. This is the only reason why hypercall is used together with memory trap algorithm, which is much more complicated than hypercall. Regards, Andrii > Ian. > -- Andrii Tseglytskyi | Embedded Dev GlobalLogic www.globallogic.com _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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