Message-ID: <7578a14b360542159ee360482e7cc579@EXMBX066.cuchost.com>
Date:   Tue, 16 May 2023 11:27:10 +0000
From:   JeeHeng Sia <jeeheng.sia@...rfivetech.com>
To:     Alexandre Ghiti <alexghiti@...osinc.com>
CC:     Song Shuai <suagrfillet@...il.com>,
        "robh@...nel.org" <robh@...nel.org>,
        Andrew Jones <ajones@...tanamicro.com>,
        "anup@...infault.org" <anup@...infault.org>,
        "palmer@...osinc.com" <palmer@...osinc.com>,
        "Leyfoon Tan" <leyfoon.tan@...rfivetech.com>,
        Mason Huo <mason.huo@...rfivetech.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Guo Ren <guoren@...nel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: Bug report: kernel paniced when system hibernates



> -----Original Message-----
> From: Alexandre Ghiti <alexghiti@...osinc.com>
> Sent: Tuesday, May 16, 2023 7:15 PM
> To: JeeHeng Sia <jeeheng.sia@...rfivetech.com>
> Cc: Song Shuai <suagrfillet@...il.com>; robh@...nel.org; Andrew Jones <ajones@...tanamicro.com>; anup@...infault.org;
> palmer@...osinc.com; Leyfoon Tan <leyfoon.tan@...rfivetech.com>; Mason Huo <mason.huo@...rfivetech.com>; Paul Walmsley
> <paul.walmsley@...ive.com>; Conor Dooley <conor.dooley@...rochip.com>; Guo Ren <guoren@...nel.org>; linux-
> riscv@...ts.infradead.org; linux-kernel@...r.kernel.org
> Subject: Re: Bug report: kernel paniced when system hibernates
> 
> Hi JeeHeng,
> 
> On Tue, May 16, 2023 at 11:55 AM JeeHeng Sia
> <jeeheng.sia@...rfivetech.com> wrote:
> >
> > Hi Song,
> >
> > Thanks for the investigation. Indeed, the exposure of the PMP reserved region to the kernel page table is causing the problem.
> > Here is the similar report: https://groups.google.com/u/0/a/groups.riscv.org/g/sw-dev/c/ITXwaKfA6z8
> 
> IMO, we should discuss the kernel related stuff on the linux riscv ML,
> I'm not subscribed to the group above and you did not answer my last
> direct emails regarding this problem either.
Hi Alex, it's strange that I haven't received a reply from you. Seems like I have forgot to update to the mailing list.
By the way, the reason hibernation failed with the recent page table is because during the initiation of the hibernation process, the hibernation core accesses the page table to check if the page can be saved. Since the page is reserved and is available to the page table, the kernel tries to access the PMP region, which causes a kernel panic. The code can be found under:
/kernel/power/snapshot.c/ line #1340
if (PageReserved(page) && (!kernel_page_present(page) || pfn_is_nosave(pfn)))
If the virtual memory is mapped to the kernel page table, then hibernation core will try to access the page.

> Thanks,
> 
> Alex
> 
> >
> > Thanks
> > Regards
> > Jee Heng
> >
> > > -----Original Message-----
> > > From: Song Shuai <suagrfillet@...il.com>
> > > Sent: Tuesday, May 16, 2023 5:24 PM
> > > To: alexghiti@...osinc.com; robh@...nel.org; Andrew Jones <ajones@...tanamicro.com>; anup@...infault.org;
> > > palmer@...osinc.com; JeeHeng Sia <jeeheng.sia@...rfivetech.com>; Leyfoon Tan <leyfoon.tan@...rfivetech.com>; Mason Huo
> > > <mason.huo@...rfivetech.com>; Paul Walmsley <paul.walmsley@...ive.com>; Conor Dooley <conor.dooley@...rochip.com>;
> Guo
> > > Ren <guoren@...nel.org>
> > > Cc: linux-riscv@...ts.infradead.org; linux-kernel@...r.kernel.org
> > > Subject: Bug report: kernel paniced when system hibernates
> > >
> > > Description of problem:
> > >
> > > The latest hibernation support[1] of RISC-V Linux produced a kernel panic.
> > > The entire log has been posted at this link: https://termbin.com/sphl .
> > >
> > > How reproducible:
> > >
> > > You can reproduce it with the following step :
> > >
> > > 1. prepare the environment with
> > > - Qemu-virt v8.0.0 (with OpenSbi v1.2)
> > > - Linux v6.4-rc1
> > >
> > > 2. start the Qemu virt
> > > ```sh
> > > $ cat ~/8_riscv/start_latest.sh
> > > #!/bin/bash
> > > /home/song/8_riscv/3_acpi/qemu/ooo/usr/local/bin/qemu-system-riscv64 \
> > > -smp 2 -m 4G -nographic -machine virt \
> > > -kernel /home/song/9_linux/linux/00_rv_test/arch/riscv/boot/Image \
> > > -append "root=/dev/vda ro eaylycon=uart8250,mmio,0x10000000
> > > early_ioremap_debug console=ttyS0 loglevel=8 memblock=debug
> > > no_console_suspend audit=0 3" \
> > > -drive file=/home/song/8_riscv/fedora/stage4-disk.img,format=raw,id=hd0 \
> > > -device virtio-blk-device,drive=hd0 \
> > > -drive file=/home/song/8_riscv/fedora/adisk.qcow2,format=qcow2,id=hd1 \
> > > -device virtio-blk-device,drive=hd1 \
> > > -gdb tcp::1236 #-S
> > > ```
> > > 3. execute hibernation
> > >
> > > ```sh
> > > swapon /dev/vdb2 # this is my swap disk
> > >
> > > echo disk > /sys/power/state
> > > ```
> > >
> > > 4. Then you will encounter the kernel panic logged in the above link
> > >
> > >
> > > Other Information:
> > >
> > > After my initial and incomplete dig-up, the commit (3335068f8721
> > > "riscv: Use PUD/P4D/PGD pages for the linear mapping")[2]
> > > is closely related to this panic. This commit uses re-defined
> > > `MIN_MEMBLOCK_ADDR` to discover the entire system memory
> > > and extends the `va_pa_offset` from `kernel_map.phys_addr` to
> > > `phys_ram_base` for linear memory mapping.
> > >
> > > If the firmware delivered the firmware memory region (like: a PMP
> > > protected region in OpenSbi) without "no-map" propriety,
> > > this commit will result in firmware memory being directly mapped by
> > > `create_linear_mapping_page_table()`.
> > >
> > > We can see the mapping via ptdump :
> > > ```c
> > > ---[ Linear mapping ]---
> > > 0xff60000000000000-0xff60000000200000 0x0000000080000000 2M PMD D A G
> > > . . W R V ------------- the firmware memory
> > > 0xff60000000200000-0xff60000000c00000 0x0000000080200000 10M PMD D A G . . . R V
> > > 0xff60000000c00000-0xff60000001000000 0x0000000080c00000 4M PMD D A G . . W R V
> > > 0xff60000001000000-0xff60000001600000 0x0000000081000000 6M PMD D A G . . . R V
> > > 0xff60000001600000-0xff60000040000000 0x0000000081600000 1002M PMD D A
> > > G . . W R V
> > > 0xff60000040000000-0xff60000100000000 0x00000000c0000000 3G PUD D A G . . W R V
> > > ---[ Modules/BPF mapping ]---
> > > ---[ Kernel mapping ]---
> > > 0xffffffff80000000-0xffffffff80a00000 0x0000000080200000 10M PMD D A G . X . R V
> > > 0xffffffff80a00000-0xffffffff80c00000 0x0000000080c00000 2M PMD D A G . . . R V
> > > 0xffffffff80c00000-0xffffffff80e00000 0x0000000080e00000 2M PMD D A G . . W R V
> > > 0xffffffff80e00000-0xffffffff81400000 0x0000000081000000 6M PMD D A G . . . R V
> > > 0xffffffff81400000-0xffffffff81800000 0x0000000081600000 4M PMD
> > > ```
> > >
> > > In the hibernation process, `swsusp_save()` calls
> > > `copy_data_pages(&copy_bm, &orig_bm)` to copy these two memory
> > > bitmaps,
> > > the Oops(load access fault) occurred while copying the page of
> > > PAGE_OFFSET (which maps the firmware memory).
> > >
> > > I also did two other tests:
> > > Test1:
> > >
> > > The hibernation works well in the kernel with the commit 3335068f8721
> > > reverted at least in the current environment.
> > >
> > > Test2:
> > >
> > > I built a simple kernel module to simulate the access of the value of
> > > `PAGE_OFFSET` address, and the same panic occurred with the load
> > > access fault.
> > > So hibernation seems not the only case to trigger this panic.
> > >
> > > Finally, should we always leave the firmware memory with
> > > `MEMBLOCK_NOMAP` flag by some efforts from Linux or OpenSbi (at least
> > > in the current environment) or any other suggestions?
> > >
> > > Please correct me if I'm wrong.
> > >
> > > [1]: https://lore.kernel.org/r/20230330064321.1008373-5-jeeheng.sia@starfivetech.com
> > > [2]: https://lore.kernel.org/r/20230324155421.271544-4-alexghiti@rivosinc.com
> > >
> > > --
> > > Thanks,
> > > Song

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