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

Nylon Chen
2024-03-12T06:40:55Z

Alexandre Ghiti <alexghiti@rivosinc.com> 於 2024年2月5日 週一 下午5:32寫道：
>
> Hi Nylon,
>
> On Fri, Jan 19, 2024 at 10:27 AM Nylon Chen <nylon.chen@sifive.com> wrote:
> >
> > Alexandre Ghiti <alexghiti@rivosinc.com> 於 2024年1月18日 週四 下午9:01寫道：
> > >
> > > Hi Nylon,
> > Hi Alexandre, thanks for your feedback,
> > >
> > > On Thu, Jan 18, 2024 at 9:23 AM Nylon Chen <nylon.chen@sifive.com> wrote:
> > > >
> > > > > 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?
> > >
> > > I guess it will end up in the memory pool and pages from openSBI
> > > region will be allocated, so we should see very quickly bad stuff
> > > happening (either PMP violation or M-mode ecall never
> > > returning/trapping/etc).
> > >
> > > But I don't observe the same thing, I always see the openSBI region
> > > being reserved:
> > >
> > > reserved[0x0] [0x0000000080000000-0x000000008007ffff],
> > > 0x0000000000080000 bytes flags: 0x0
> > >
> > > Can you elaborate a bit more about "When consecutive memblocks are
> > > merged, if the memblock types are different, they will be merged into
> > > memory"? Where/when does this merge happen? Can you give me a config
> > > file and a kernel revision so that I can take a look?
> > Ok, If you want to reproduce the same results you just need to modify OpenSBI
> >
> > [ lib/sbi/sbi_domain.c ]
> > +#define TEST_SIZE 0x200000
> >
> > - (scratch->fw_size - scratch->fw_rw_offset),
> > + (TEST_SIZE - scratch->fw_rw_offset),
> >
> > In addition, you can insert checks in the kernel merged function
> > [ mm/memblock.c ]
> > static void __init_memblock memblock_merge_regions(struct memblock_type *type)
> > while (i < type->cnt - 1) {
> > ...
> > /* move forward from next + 1, index of which is i + 2 */
> > memmove(next, next + 1, (type->cnt - (i + 2)) * sizeof(*next));
> > type->cnt--;
> > }
> > + pr_info("Merged memblock_type: cnt = %lu, max = %lu,
> > total_size = 0x%llx\n",type->cnt, type->max, type->total_size);
> > + for (i = 0; i < type->cnt; i++) {
> > + const char *region_type =
> > memblock_is_memory(type->regions[i].base) ? "memory" : "reserve";
> > + pr_info("Region %d: base = 0x%llx, size = 0x%llx, type
> > = %s\n", i, type->regions[i].base, type->regions[i].size,
> > region_type);
> > + }
> > }
> > This is kernel boot log
> > - before your patch
> > ...
> > [ 0.000000] OF: fdt: Reserving memory: base = 0x80000000, size = 0x200000
> > [ 0.000000] Merged memblock_type: cnt = 4, max = 128, total_size = 0x1628501
> > [ 0.000000] Region 0: base = 0x80000000, size = 0x1600000, type = reserve
> > ...
> >
> > - after your patch
> > ...
> > [ 0.000000] OF: fdt: Reserving memory: base = 0x80000000, size = 0x200000
> > [ 0.000000] Merged memblock_type: cnt = 4, max = 128, total_size = 0x180c42e
> > [ 0.000000] Region 0: base = 0x80000000, size = 0x1800000, type = memory
>
Hi Alex, thanks for your feedback.
> So the openSBI region is marked as memory, and not reserved because
> this region is now described as nomap, and memblock_mark_nomap() does
> not move this region into the reserved memblock list, but keep it in
> the memory list with the nomap flag
> (https://elixir.bootlin.com/linux/latest/source/drivers/of/fdt.c#L479).
> But as stated in the description of memblock_mark_nomap()
> (https://elixir.bootlin.com/linux/latest/source/mm/memblock.c#L969),
> the pages associated with the region will be marked as PageReserved
> and the region will not be covered in the linear mapping.
I traced it via GDB, and indeed, it enters
early_init_dt_reserve_memory() and calls memblock_reserve to reserve
this block of memory.

[before your patch]
[ 0.000000] OF: fdt: check nomap Reserving memory: base =
0x80000000, size = 0x200000
[ 0.000000] --- Reserved memory: Base address: 80000000, Size:
200000---
[ 0.000000] Merged memblock_type: cnt = 4, max = 128, total_size =
0x1e28501
[ 0.000000] Region 0: base = 0x80000000, size = 0x1e00000, type =
reserve
[ 0.000000] Region 1: base = 0xbfe00000, size = 0x6002, type =
memory
....
[ 0.000000] OF: fdt: Reserved memory: reserved region for node
'mmode_resv0@80000000': base 0x0000000080000000, size 2 MiB
[ 0.000000] OF: reserved mem:
0x0000000080000000..0x00000000801fffff (2048 KiB) map non-reusable
mmode_resv0@80000000

[after your patch]
[ 0.000000] OF: fdt: check nomap Reserving memory: base =
0x80000000, size = 0x200000
[ 0.000000] --- Reserved memory: Base address: 80000000, Size: 200000---
[ 0.000000] Merged memblock_type: cnt = 4, max = 128, total_size = 0x1e25501
[ 0.000000] Region 0: base = 0x80000000, size = 0x1e00000, type = memory
[ 0.000000] Region 1: base = 0xbfe00000, size = 0x6002, type = memory
...
[ 0.000000] OF: fdt: Reserved memory: reserved region for node
'mmode_resv0@80000000': base 0x0000000080000000, size 2 MiB
[ 0.000000] OF: reserved mem:
0x0000000080000000..0x00000000801fffff (2048 KiB) map non-reusable
mmode_resv0@80000000

At the moment, it can be confirmed that there is no need to worry
about this block of memory being used.

But I still have a question I'd like to ask, which is why this
location is flagged as 'reserve' instead of 'memory' in the memblock

Thanks,
Nylon
>
> So to me, this is normal and we are safe. Let me know if I made a mistake.
>
> And sorry for the long delay, that slipped my mind!
>
> Thanks,
>
> Alex
>
> > ...
> > [ 0.000000] Failed to add a system RAM resource at 80200000
> > ...
> > >
> > > Thanks,
> > >
> > > Alex
> > >
> > > > >
> > > > > 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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