linux-kernel - Re: [GIT PULL] Please pull HMM changes

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Date:   Mon, 30 Mar 2020 12:54:03 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Jason Gunthorpe <jgg@...lanox.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Subject: Re: [GIT PULL] Please pull HMM changes

On Mon, Mar 30, 2020 at 02:57:48PM -0300, Jason Gunthorpe wrote:
> Hi Linus,
> 
> This series arose from a review of hmm_range_fault() by Christoph, Ralph and
> myself. Several bug fixes and some general clarity.
> 
> hmm_range_fault() is being used by these 'SVM' style drivers to
> non-destructively read the page tables. It is very similar to get_user_pages()
> except that the output is an array of PFNs and per-pfn flags, and it has
> various modes of reading.
> 
> This is necessary before RDMA ODP can be converted, as we don't want to have
> weird corner case regressions, which is still a looking forward item. Ralph
> has a nice tester for this routine, but it is waiting for feedback from the
> selftests maintainers.
> 
> Regards,
> Jason
> 
> The following changes since commit f8788d86ab28f61f7b46eb6be375f8a726783636:
> 
>   Linux 5.6-rc3 (2020-02-23 16:17:42 -0800)
> 
> are available in the Git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git tags/for-linus-hmm
> 
> for you to fetch changes up to 9cee0e8c6f1eb4b5e56d3eb7f5d47b05637bab4f:
> 
>   mm/hmm: return error for non-vma snapshots (2020-03-27 20:19:25 -0300)
> 
> ----------------------------------------------------------------
> hmm related patches for 5.7
> 
> This series focuses on corner case bug fixes and general clarity
> improvements to hmm_range_fault().
> 
> - 9 bug fixes
> 
> - Allow pgmap to track the 'owner' of a DEVICE_PRIVATE - in this case the
>   owner tells the driver if it can understand the DEVICE_PRIVATE page or
>   not. Use this to resolve a bug in nouveau where it could touch
>   DEVICE_PRIVATE pages from other drivers.
> 
> - Remove a bunch of dead, redundant or unused code and flags
> 
> - Clarity improvements to hmm_range_fault()
> 
> ----------------------------------------------------------------
> Christoph Hellwig (9):
>       mm/hmm: don't provide a stub for hmm_range_fault()
>       mm/hmm: remove the unused HMM_FAULT_ALLOW_RETRY flag
>       mm/hmm: simplify hmm_vma_walk_hugetlb_entry()
>       mm/hmm: don't handle the non-fault case in hmm_vma_walk_hole_()
>       mm: merge hmm_vma_do_fault into into hmm_vma_walk_hole_
>       memremap: add an owner field to struct dev_pagemap
>       mm: handle multiple owners of device private pages in migrate_vma
>       mm: simplify device private page handling in hmm_range_fault
>       mm/hmm: check the device private page owner in hmm_range_fault()
> 
> Jason Gunthorpe (17):
>       mm/hmm: add missing unmaps of the ptep during hmm_vma_handle_pte()
>       mm/hmm: do not call hmm_vma_walk_hole() while holding a spinlock
>       mm/hmm: add missing pfns set to hmm_vma_walk_pmd()
>       mm/hmm: add missing call to hmm_range_need_fault() before returning EFAULT
>       mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()
>       mm/hmm: return -EFAULT when setting HMM_PFN_ERROR on requested valid pages
>       mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling
>       mm/hmm: do not check pmd_protnone twice in hmm_vma_handle_pmd()
>       mm/hmm: remove pgmap checking for devmap pages
>       mm/hmm: return the fault type from hmm_pte_need_fault()
>       mm/hmm: remove unused code and tidy comments
>       mm/hmm: remove HMM_FAULT_SNAPSHOT
>       mm/hmm: remove the CONFIG_TRANSPARENT_HUGEPAGE #ifdef

This patch causes an error on arm32 all{mod,yes}config because pmd_pfn
is only defined when CONFIG_ARM_LPAE is set, which is a dependency of
CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE and CONFIG_TRANSPARENT_HUGEPAGE.

$ make -j$(nproc) -s ARCH=arm CC=clang CROSS_COMPILE=arm-linux-gnueabi- O=out/arm32 distclean allyesconfig mm/hmm.o
mm/hmm.c:207:8: error: implicit declaration of function 'pmd_pfn'
[-Werror,-Wimplicit-function-declaration]
        pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
                      ^
1 error generated.

https://elixir.bootlin.com/linux/v5.6/source/arch/arm/include/asm/pgtable-3level.h#L236
https://elixir.bootlin.com/linux/v5.6/source/arch/arm/include/asm/pgtable.h#L29
https://elixir.bootlin.com/linux/v5.6/source/arch/arm/Kconfig#L1579

No idea how to rectify that but thought I would let you know.

Cheers,
Nathan