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From: Nylon Chen <nylon.chen@sifive.com>
Date: Tue, 12 Mar 2024 14:48:30 +0800
Message-ID: <CAHh=Yk8cWiX8q7YT3OuqNBP=kgNdZm3cWZCm01+CfVVQcnPy=Q@mail.gmail.com>
Subject: Re: Fwd: [PATCH v8 0/4] riscv: Use PUD/P4D/PGD pages for the linear mapping
To: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: alex@ghiti.fr, apatel@ventanamicro.com, catalin.marinas@arm.com, 
	will@kernel.org, paul.walmsley@sifive.com, palmer@dabbelt.com, 
	aou@eecs.berkeley.edu, robh+dt@kernel.org, frowand.list@gmail.com, 
	rppt@kernel.org, akpm@linux-foundation.org, anup@brainfault.org, 
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, 
	linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, 
	linux-mm@kvack.org, zong.li@sifive.com, nylon7717@gmail.com
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Nylon Chen <nylon.chen@sifive.com> =E6=96=BC 2024=E5=B9=B43=E6=9C=8812=E6=
=97=A5 =E9=80=B1=E4=BA=8C =E4=B8=8B=E5=8D=882:40=E5=AF=AB=E9=81=93=EF=BC=9A
>
> Alexandre Ghiti <alexghiti@rivosinc.com> =E6=96=BC 2024=E5=B9=B42=E6=9C=
=885=E6=97=A5 =E9=80=B1=E4=B8=80 =E4=B8=8B=E5=8D=885:32=E5=AF=AB=E9=81=93=
=EF=BC=9A
> >
> > Hi Nylon,
> >
> > On Fri, Jan 19, 2024 at 10:27=E2=80=AFAM Nylon Chen <nylon.chen@sifive.=
com> wrote:
> > >
> > > Alexandre Ghiti <alexghiti@rivosinc.com> =E6=96=BC 2024=E5=B9=B41=E6=
=9C=8818=E6=97=A5 =E9=80=B1=E5=9B=9B =E4=B8=8B=E5=8D=889:01=E5=AF=AB=E9=81=
=93=EF=BC=9A
> > > >
> > > > Hi Nylon,
> > > Hi Alexandre, thanks for your feedback,
> > > >
> > > > On Thu, Jan 18, 2024 at 9:23=E2=80=AFAM Nylon Chen <nylon.chen@sifi=
ve.com> wrote:
> > > > >
> > > > > > On 3/23/23 15:55, Anup Patel wrote:
> > > > > > > On Thu, Mar 23, 2023 at 6:24=E2=80=AFPM Alexandre Ghiti <alex=
ghiti@rivosinc.com> wrote:
> > > > > > >> Hi Anup,
> > > > > > >>
> > > > > > >> On Thu, Mar 23, 2023 at 1:18=E2=80=AFPM Anup Patel <apatel@v=
entanamicro.com> wrote:
> > > > > > >>> Hi Alex,
> > > > > > >>>
> > > > > > >>> On Thu, Mar 16, 2023 at 6:48=E2=80=AFPM Alexandre Ghiti <al=
exghiti@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 enabl=
ed, 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 pe=
rmissions to
> > > > > > >>>> the whole region: it is achieved by introducing a new memb=
lock API.
> > > > > > >>>>
> > > > > > >>>> Another patch makes use of this new API in arm64 which use=
d some sort of
> > > > > > >>>> hack to solve this issue: it was built/boot tested success=
fully.
> > > > > > >>>>
> > > > > > >>>> 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_memo=
ry 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 unsi=
gned long
> > > > > > >>>>
> > > > > > >>>> v5:
> > > > > > >>>> - Fix nommu builds by getting rid of riscv_pfn_base in pat=
ch 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 t=
hat 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 line=
ar mapping
> > > > > > >>>>    riscv: Use PUD/P4D/PGD pages for the linear mapping
> > > > > > >>> Kernel boot fine on RV64 but there is a failure which is st=
ill not
> > > > > > >>> addressed. You can see this failure as following message in
> > > > > > >>> kernel boot log:
> > > > > > >>>      0.000000] Failed to add a System RAM resource at 80200=
000
> > > > > > >> Hmmm I don't get that in any of my test configs, would you m=
ind
> > > > > > >> 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 -kerne=
l
> > > > > > > ./build-riscv64/arch/riscv/boot/Image -append "root=3D/dev/ra=
m rw
> > > > > > > console=3DttyS0 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 dif=
ferent,
> > > > > 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 cha=
nged
> > > > > 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 in=
to
> > > > memory"? Where/when does this merge happen? Can you give me a confi=
g
> > > > 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_ty=
pe *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)) * sizeo=
f(*next));
> > >                 type->cnt--;
> > >         }
> > > +       pr_info("Merged memblock_type: cnt =3D %lu, max =3D %lu,
> > > total_size =3D 0x%llx\n",type->cnt, type->max, type->total_size);
> > > +       for (i =3D 0; i < type->cnt; i++) {
> > > +               const char *region_type =3D
> > > memblock_is_memory(type->regions[i].base) ? "memory" : "reserve";
> > > +               pr_info("Region %d: base =3D 0x%llx, size =3D 0x%llx,=
 type
> > > =3D %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 =3D 0x80000000, size =
=3D 0x200000
> > > [    0.000000] Merged memblock_type: cnt =3D 4, max =3D 128, total_si=
ze =3D 0x1628501
> > > [    0.000000] Region 0: base =3D 0x80000000, size =3D 0x1600000, typ=
e =3D reserve
> > > ...
> > >
> > > - after your patch
> > > ...
> > > [    0.000000] OF: fdt: Reserving memory: base =3D 0x80000000, size =
=3D 0x200000
> > > [    0.000000] Merged memblock_type: cnt =3D 4, max =3D 128, total_si=
ze =3D 0x180c42e
> > > [    0.000000] Region 0: base =3D 0x80000000, size =3D 0x1800000, typ=
e =3D 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 =3D
> 0x80000000, size =3D 0x200000
> [    0.000000] ---  Reserved memory: Base address: 80000000, Size:
> 200000---
> [    0.000000] Merged memblock_type: cnt =3D 4, max =3D 128, total_size =
=3D
> 0x1e28501
> [    0.000000] Region 0: base =3D 0x80000000, size =3D 0x1e00000, type =
=3D
> reserve
> [    0.000000] Region 1: base =3D 0xbfe00000, size =3D 0x6002, type =3D
> 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 =3D
> 0x80000000, size =3D 0x200000
> [    0.000000] --- Reserved memory: Base address: 80000000, Size: 200000-=
--
> [    0.000000] Merged memblock_type: cnt =3D 4, max =3D 128, total_size =
=3D 0x1e25501
> [    0.000000] Region 0: base =3D 0x80000000, size =3D 0x1e00000, type =
=3D memory
> [    0.000000] Region 1: base =3D 0xbfe00000, size =3D 0x6002, type =3D m=
emory
> ...
> [    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
Sorry, I asked the wrong question.

Why is this location marked as "memory" instead of "reserve" in the membloc=
k?
>
> Thanks,
> Nylon
> >
> > So to me, this is normal and we are safe. Let me know if I made a mista=
ke.
> >
> > 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 an=
d that
> > > > > > the simplest solution is to re-merge the memblock regions after=
wards
> > > > > > (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 advantag=
e of that
> > > > > > to clean setup_vm_final which I have wanted to do for a long ti=
me.
> > > > > >
> > > > > > @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
> > > > > > >>>>
> > > > > > > _______________________________________________
> > > > > > > linux-riscv mailing list
> > > > > > > linux-riscv@lists.infradead.org
> > > > > > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> > > > > >
> > > > > > _______________________________________________
> > > > > > linux-riscv mailing list
> > > > > > linux-riscv@lists.infradead.org
> > > > > > http://lists.infradead.org/mailman/listinfo/linux-riscv