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

From: Logan Gunthorpe
Date: Fri Apr 26 2019 - 12:37:27 EST

On 2019-04-24 5:23 p.m., Palmer Dabbelt wrote:
On Wed, 27 Mar 2019 14:36:36 PDT (-0700), logang@xxxxxxxxxxxx wrote:

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,
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

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: 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

Thanks for the note. I've queued up the fixes for this. However, I'm still a bit stuck on the memory hot remove stuff. I'm waiting for the similar work in arm64 to be done so I can reuse some of it[1].

The first patch of this series that implements sparsemem builds on rv32 and was generally accepted in previous cycles; so I'd appreciate if you can pick that one up for v5.2.