[PATCH v8 0/4] riscv: Use PUD/P4D/PGD pages for the linear mapping

Alexandre Ghiti
2023-03-16T14:31:47Z

This patchset intends to improve tlb utilization by using hugepages for
the linear mapping.

As reported by Anup in v6, when STRICT_KERNEL_RWX is enabled, we must
take care of isolating the kernel text and rodata so that they are not
mapped with a PUD mapping which would then assign wrong permissions to
the whole region: it is achieved by introducing a new memblock API.

Another patch makes use of this new API in arm64 which used some sort of
hack to solve this issue: it was built/boot tested successfully.

base-commit-tag: v6.3-rc1

v8:
- Fix rv32, as reported by Anup
- Do not modify memblock_isolate_range and fixes comment, as suggested by Mike
- Use the new memblock API for crash kernel too in arm64, as suggested by Andrew
- Fix arm64 double mapping (which to me did not work in v7), but ends up not
being pretty at all, will wait for comments from arm64 reviewers, but
this patch can easily be dropped if they do not want it.

v7:
- Fix Anup bug report by introducing memblock_isolate_memory which
allows us to split the memblock mappings and then avoid to map the
the PUD which contains the kernel as read only
- Add a patch to arm64 to use this newly introduced API

v6:
- quiet LLVM warning by casting phys_ram_base into an unsigned long

v5:
- Fix nommu builds by getting rid of riscv_pfn_base in patch 1, thanks
Conor
- Add RB from Andrew

v4:
- Rebase on top of v6.2-rc3, as noted by Conor
- Add Acked-by Rob

v3:
- Change the comment about initrd_start VA conversion so that it fits
ARM64 and RISCV64 (and others in the future if needed), as suggested
by Rob

v2:
- Add a comment on why RISCV64 does not need to set initrd_start/end that
early in the boot process, as asked by Rob

Alexandre Ghiti (4):
riscv: Get rid of riscv_pfn_base variable
mm: Introduce memblock_isolate_memory
arm64: Make use of memblock_isolate_memory for the linear mapping
riscv: Use PUD/P4D/PGD pages for the linear mapping

arch/arm64/mm/mmu.c | 25 +++++++++++------
arch/riscv/include/asm/page.h | 19 +++++++++++--
arch/riscv/mm/init.c | 53 ++++++++++++++++++++++++++++-------
arch/riscv/mm/physaddr.c | 16 +++++++++++
drivers/of/fdt.c | 11 ++++----
include/linux/memblock.h | 1 +
mm/memblock.c | 20 +++++++++++++
7 files changed, 119 insertions(+), 26 deletions(-)

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2.37.2