Messages in this thread | | | Date | Sat, 20 May 2023 22:22:36 -0500 | From | Samuel Holland <> | Subject | Re: riscv: boot failure for 3335068f8721 ("riscv: Use PUD/P4D/PGD pages for the linear mapping") |
| |
Hi Drew,
On 5/20/23 21:05, Drew Fustini wrote: > Hello, I tested 6.4-rc1 on an internal RISC-V SoC and observed a boot > failure on a Store/AMO access fault (exception code 7) in __memset(). > stval (e.g. badaddr) was set to 0xffffaf8000000000. This SoC is RV64GC > with Sv48 so it seems that address is the start of the "direct mapping > of all physical memory" [1]. > > The 6.3 release boots okay and the system is able to operate correctly > with an Ubuntu 23.04 rootfs on eMMC. Therefore, I decided to bisect and > I found the failure begins with 3335068f8721 ("riscv: Use PUD/P4D/PGD > pages for the linear mapping"). The system boots okay with the prior > commit 8589e346bbb6 ("riscv: Move the linear mapping creation in its > own function"). > > The boot log [2] shows that the fault happens right after buildroot's > init script [3] uses switch_root to execute init from the Ubuntu rootfs > on the eMMC. > > DWARF4 is enabled in .config [4] and the decoded stack trace [5] shows: > > epc : __memset (/eng/dfustini/gitlab/linux/arch/riscv/lib/memset.S:67) > > From memset.S: > > Line 67: REG_S a1, 0(t0) > > From the oops: > > epc : ffffffff81122d6c ra : ffffffff80218504 sp : ffffaf8002e47500 > gp : ffffffff82695010 tp : ffffaf8002e2ec00 t0 : ffffaf8000000000 > t1 : 0000000000000080 t2 : 0000000000000001 s0 : ffffaf8002e47550 > s1 : ffff8d8200000040 a0 : ffffaf8000000000 a1 : 0000000000000000 > > Thus I think it is trying to store 0x0 to 0xffffaf8000000000 which is > the start of the direct map. From the boot log [2], OpenSBI shows: > > Domain0 Region00 : 0x0000000002080000-0x00000000020bffff M: (I,R,W) S/U: () > Domain0 Region01 : 0x0000008000000000-0x000000800003ffff M: (R,W,X) S/U: () > Domain0 Region02 : 0x0000000002000000-0x000000000207ffff M: (I,R,W) S/U: () > Domain0 Region03 : 0x0000000000000000-0xffffffffffffffff M: (R,W,X) S/U: (R,W,X) > > The DDR memory on this SoC starts at 0x8000000000 with size 2GB. The > memory node from the device tree [6]: > > memory@8000000000 { > device_type = "memory"; > reg = <0x80 0 0x00000000 0x80000000>; > }; > > I think the direct map address 0xffffaf8000000000 would map to physical > address 0x8000000000. Thus I think the attempted store in S-mode to that > address would violate the PMP settings for Region01. > > I do not yet understand why this happens with 3335068f8721 ("riscv: Use > PUD/P4D/PGD pages for the linear mapping") but not for the prior commit > 8589e346bbb6 ("riscv: Move the linear mapping creation in its own > function").
Where does Linux's DTB come from? It should be the one that was modified by OpenSBI to add a reserved-memory node matching PMP Region01 (fdt_reserved_memory_fixup()).
Before this commit, Linux ignored the first 2 MiB of physical RAM. So if OpenSBI was loaded in this region, you could get away with ignoring the firmware-provided DTB; now you actually need to use it, as intended.
Regards, Samuel
| |