Re: [PATCH 0/7] RISC-V: Sparsmem, Memory Hotplug and pte_devmap for P2P

[Palmer Dabbelt]

On Wed, 27 Mar 2019 14:36:36 PDT (-0700), logang@xxxxxxxxxxxx wrote:
> Hi,
>
> This patchset enables P2P on the RISC-V architecture. To do this on the
> current kernel, we only need to be able to back IO memory with struct
> pages using devm_memremap_pages(). This requires ARCH_HAS_ZONE_DEVICE,
> ARCH_ENABLE_MEMORY_HOTPLUG, and ARCH_ENABLE_MEMORY_HOTREMOVE; which in
> turn requires ARCH_SPARSEMEM_ENABLE. We also need to ensure that the
> IO memory regions in hardware can be covered by the linear region
> so that there is a linear relation ship between the virtual address and
> the struct page address in the vmemmap region.
>
> While our reason to do this work is for P2P, these features are all
> useful, more generally, and also enable other kernel features.
>
> The first patch in the series implements sparse mem. It was already
> submitted and reviewed last cycle, only forgotten. It has been rebased
> onto v5.1-rc2.
>
> Patches 2 through 4 rework the architecture's virtual address space
> mapping trying to get as much of the IO regions covered by the linear
> mapping. With Sv39, we do not have enough address space to cover all the
> typical hardware regions but we can get the majority of it.
>
> Patch 5 and 6 implement memory hotplug and remove. These are relatively
> straight forward additions similar to other arches.
>
> Patch 7 implements pte_devmap which allows us to set
> ARCH_HAS_ZONE_DEVICE.
>
> The patchset was tested in QEMU and on a HiFive Unleashed board.
> However, we were unable to actually test P2P transactions with this
> exact set because we have been unable to get PCI working with v5.1-rc2.
> We were able to get it running on a 4.19 era kernel (with a bunch of
> out-of-tree patches for PCI on a Microsemi PolarFire board).
>
> This series is based on v5.1-rc2 and a git tree is available here:
>
> https://github.com/sbates130272/linux-p2pmem riscv-p2p-v1

Looks like these don't build on rv32 when applied on top of 5.1-rc6.  We now
have rv32_defconfig, which should make it easier to tests these sorts of
things.