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

Nylon Chen
2024-01-18T08:24:22Z

> On 3/23/23 15:55, Anup Patel wrote:
> > On Thu, Mar 23, 2023 at 6:24 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
> >> Hi Anup,
> >>
> >> On Thu, Mar 23, 2023 at 1:18 PM Anup Patel <apatel@ventanamicro.com> wrote:
> >>> Hi Alex,
> >>>
> >>> On Thu, Mar 16, 2023 at 6:48 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
> >>>> 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
> >>> Kernel boot fine on RV64 but there is a failure which is still not
> >>> addressed. You can see this failure as following message in
> >>> kernel boot log:
> >>> 0.000000] Failed to add a System RAM resource at 80200000
> >> Hmmm I don't get that in any of my test configs, would you mind
> >> sharing yours and your qemu command line?
> > Try alexghiti_test branch at
> > https://github.com/avpatel/linux.git
> >
> > I am building the kernel using defconfig and my rootfs is
> > based on busybox.
> >
> > My QEMU command is:
> > qemu-system-riscv64 -M virt -m 512M -nographic -bios
> > opensbi/build/platform/generic/firmware/fw_dynamic.bin -kernel
> > ./build-riscv64/arch/riscv/boot/Image -append "root=/dev/ram rw
> > console=ttyS0 earlycon" -initrd ./rootfs_riscv64.img -smp 4
>
>
> So splitting memblock.memory is the culprit, it "confuses" the resources
> addition and I can only find hacky ways to fix that...
Hi Alexandre,

We encountered the same error as Anup. After adding your patch
(3335068f87217ea59d08f462187dc856652eea15), we will not encounter the
error again.

What I have observed so far is

- before your patch
When merging consecutive memblocks, if the memblock types are different,
they will be merged into reserved
- after your patch
When consecutive memblocks are merged, if the memblock types are
different, they will be merged into memory.

Such a result will cause the memory location of OpenSBI to be changed
from reserved to memory. Will this have any side effects?
>
> So given that the arm64 patch with the new API is not pretty and that
> the simplest solution is to re-merge the memblock regions afterwards
> (which is done by memblock_clear_nomap), I'll drop the new API and the
> arm64 patch to use the nomap API like arm64: I'll take advantage of that
> to clean setup_vm_final which I have wanted to do for a long time.
>
> @Mike Thanks for you reviews!
>
> @Anup Thanks for all your bug reports on this patchset, I have to
> improve my test flow (it is in the work :)).
>
>
> > Regards,
> > Anup
> >
> >> Thanks
> >>
> >>> Regards,
> >>> Anup
> >>>
> >>>> 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(-)
> >>>>
> >>>> --
> >>>> 2.37.2
> >>>>
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>
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