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

Alexandre Ghiti
2023-03-24T10:00:28Z

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...

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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