> -----Original Message----- > From: Jon Nettleton [mailto:jon@xxxxxxxxxxxxx] > Sent: 16 September 2021 08:52 > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx> > Cc: Robin Murphy <robin.murphy@xxxxxxx>; Lorenzo Pieralisi > <lorenzo.pieralisi@xxxxxxx>; Laurentiu Tudor <laurentiu.tudor@xxxxxxx>; > linux-arm-kernel <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; ACPI Devel Maling > List <linux-acpi@xxxxxxxxxxxxxxx>; Linux IOMMU > <iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx>; Joerg Roedel <joro@xxxxxxxxxx>; Will > Deacon <will@xxxxxxxxxx>; wanghuiqiang <wanghuiqiang@xxxxxxxxxx>; > Guohanjun (Hanjun Guo) <guohanjun@xxxxxxxxxx>; Steven Price > <steven.price@xxxxxxx>; Sami Mujawar <Sami.Mujawar@xxxxxxx>; Eric > Auger <eric.auger@xxxxxxxxxx>; yangyicong <yangyicong@xxxxxxxxxx> > Subject: Re: [PATCH v7 2/9] ACPI/IORT: Add support for RMR node parsing > > On Thu, Sep 16, 2021 at 9:26 AM Shameerali Kolothum Thodi > <shameerali.kolothum.thodi@xxxxxxxxxx> wrote: > > > > > > > > > -----Original Message----- > > > From: Jon Nettleton [mailto:jon@xxxxxxxxxxxxx] > > > Sent: 06 September 2021 20:51 > > > To: Robin Murphy <robin.murphy@xxxxxxx> > > > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>; Shameerali > > > Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>; Laurentiu > > > Tudor <laurentiu.tudor@xxxxxxx>; linux-arm-kernel > > > <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; ACPI Devel Maling List > > > <linux-acpi@xxxxxxxxxxxxxxx>; Linux IOMMU > > > <iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx>; Linuxarm <linuxarm@xxxxxxxxxx>; > > > Joerg Roedel <joro@xxxxxxxxxx>; Will Deacon <will@xxxxxxxxxx>; > > > wanghuiqiang <wanghuiqiang@xxxxxxxxxx>; Guohanjun (Hanjun Guo) > > > <guohanjun@xxxxxxxxxx>; Steven Price <steven.price@xxxxxxx>; Sami > > > Mujawar <Sami.Mujawar@xxxxxxx>; Eric Auger > <eric.auger@xxxxxxxxxx>; > > > yangyicong <yangyicong@xxxxxxxxxx> > > > Subject: Re: [PATCH v7 2/9] ACPI/IORT: Add support for RMR node > > > parsing > > > > > [...] > > > > > > > > > > > > On the prot value assignment based on the remapping flag, I'd > > > > > like to hear Robin/Joerg's opinion, I'd avoid being in a > > > > > situation where "normally" this would work but then we have to quirk > it. > > > > > > > > > > Is this a valid assumption _always_ ? > > > > > > > > No. Certainly applying IOMMU_CACHE without reference to the > > > > device's _CCA attribute or how CPUs may be accessing a shared > > > > buffer could lead to a loss of coherency. At worst, applying > > > > IOMMU_MMIO to a device-private buffer *could* cause the device to > > > > lose coherency with itself if the memory underlying the RMR may > > > > have allocated into system caches. Note that the expected use for > > > > non-remappable RMRs is the device holding some sort of long-lived > > > > private data in system RAM - the MSI doorbell trick is far more of a niche > hack really. > > > > > > > > At the very least I think we need to refer to the device's memory > > > > access properties here. > > > > > > > > Jon, Laurentiu - how do RMRs correspond to the EFI memory map on > > > > your firmware? I'm starting to think that as long as the > > > > underlying memory is described appropriately there then we should > > > > be able to infer correct attributes from the EFI memory type and flags. > > > > > > The devices are all cache coherent and marked as _CCA, 1. The > > > Memory regions are in the virt table as > ARM_MEMORY_REGION_ATTRIBUTE_DEVICE. > > > > > > The current chicken and egg problem we have is that during the > > > fsl-mc-bus initialization we call > > > > > > error = acpi_dma_configure_id(&pdev->dev, DEV_DMA_COHERENT, > > > &mc_stream_id); > > > > > > which gets deferred because the SMMU has not been initialized yet. > > > Then we initialize the RMR tables but there is no device reference > > > there to be able to query device properties, only the stream id. > > > After the IORT tables are parsed and the SMMU is setup, on the > > > second device probe we associate everything based on the stream id > > > and the fsl-mc-bus device is able to claim its 1-1 DMA mappings. > > > > Can we solve this order problem by delaying the > > iommu_alloc_resv_region() to the iommu_dma_get_rmr_resv_regions(dev, > > list) ? We could invoke > > device_get_dma_attr() from there which I believe will return the _CCA > attribute. > > > > Or is that still early to invoke that? > > That looks like it should work. Do we then also need to parse through the > VirtualMemoryTable matching the start and end addresses to determine the > other memory attributes like MMIO? Yes. But that looks tricky as I can't find that readily available on Arm, like the efi_mem_attributes(). I will take a look. Please let me know if there is one or any other easy way to retrieve it. Thanks, Shameer > > -Jon > > > > > Thanks, > > Shameer > > > > > cat /sys/kernel/iommu_groups/0/reserved_regions > > > 0x0000000001000000 0x0000000010ffffff direct-relaxable > > > 0x0000000008000000 0x00000000080fffff msi > > > 0x000000080c000000 0x000000081bffffff direct-relaxable > > > 0x0000001c00000000 0x0000001c001fffff direct-relaxable > > > 0x0000002080000000 0x000000209fffffff direct-relaxable > > > > > > -Jon > > > > > > > > > > > Robin.
