Date:   Mon, 11 May 2020 17:23:30 +0200
From:   Mian Yousaf Kaukab <ykaukab@...e.de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     talho@...dia.com, thierry.reding@...il.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, afaerber@...e.de
Subject: Re: arm64: tegra186: bpmp: kernel crash while decompressing initrd

On Mon, May 11, 2020 at 12:25:00PM +0100, Robin Murphy wrote:
> On 2020-05-08 9:40 am, Mian Yousaf Kaukab wrote:
> > I am seeing following kernel crash on Jetson TX2. Board is flashed with
> > firmware bits from L4T R32.4.2 with upstream u-boot. Crash always
> > happens while decompressing initrd. Initrd is approximately 80 MiB in
> > size and compressed with xz (xz --check=crc32 --lzma2=dict=32MiB).
> > Crash is not observed if the same initrd is compressed with gzip.
> > [1] was a previous attempt to workaround the same issue.
> > 
> > [    0.651168] Trying to unpack rootfs image as initramfs...
> > [    2.890171] SError Interrupt on CPU0, code 0xbf40c000 -- SError
> > [    2.890174] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G S                5.7.0-rc4-next-20200505 #22
> > [    2.890175] Hardware name: nvidia p2771-0000/p2771-0000, BIOS 2020.04-rc3 03/25/2020
> > [    2.890176] pstate: 20000005 (nzCv daif -PAN -UAO BTYPE=--)
> > [    2.890177] pc : lzma_main+0x648/0x908
> > [    2.890178] lr : lzma_main+0x330/0x908
> > [    2.890179] sp : ffff80001003bb70
> > [    2.890180] x29: ffff80001003bb70 x28: 0000000004d794a4
> > [    2.890183] x27: 0000000004769941 x26: ffff0001eb064000
> > [    2.890185] x25: ffff0001eb060028 x24: 0000000000000002
> > [    2.890187] x23: 0000000000000003 x22: 0000000000000007
> > [    2.890189] x21: 0000000000611f4b x20: ffff0001eb060000
> > [    2.890192] x19: ffff80001003bcb8 x18: 0000000000000068
> > [    2.890194] x17: 00000000000000c0 x16: fffffe00076b2108
> > [    2.890196] x15: 0000000000000800 x14: 0000000000ffffff
> > [    2.890198] x13: 0000000000000001 x12: ffff0001eb060000
> > [    2.890200] x11: 0000000000000600 x10: ffff0001eb060028
> > [    2.890202] x9 : 00000000ffbb2a08 x8 : 0000000000000ed0
> > [    2.890204] x7 : 00000000011553ec x6 : 0000000000000000
> > [    2.890206] x5 : 0000000000000000 x4 : 0000000000000006
> > [    2.890208] x3 : 00000000015a29e4 x2 : ffff0001eb062d0c
> > [    2.890210] x1 : 000000000000000c x0 : 000000000263de44
> > 
> > With some debugging aid ported from Nvidia downstream kernel [2] the
> > actual cause was found:
> > 
> > [    0.761525] Trying to unpack rootfs image as initramfs...
> > [    2.955499] CPU0: SError: mpidr=0x80000100, esr=0xbf40c000
> > [    2.955502] CPU1: SError: mpidr=0x80000000, esr=0xbe000000
> > [    2.955505] CPU2: SError: mpidr=0x80000001, esr=0xbe000000
> > [    2.955506] CPU3: SError: mpidr=0x80000101, esr=0xbf40c000
> > [    2.955507] ROC:CCE Machine Check Error:
> > [    2.955508] ROC:CCE Registers:
> > [    2.955509]  STAT: 0xb400000000400415
> > [    2.955510]  ADDR: 0x400c00e7a00c
> > [    2.955511]  MSC1: 0x80ffc
> > [    2.955512]  MSC2: 0x3900000000800
> > [    2.955513] --------------------------------------
> > [    2.955514] Decoded ROC:CCE Machine Check:
> > [    2.955515]  Uncorrected (this is fatal)
> > [    2.955516]  Error reporting enabled when error arrived
> > [    2.955517]  Error Code = 0x415
> > [    2.955518]  Poison Error
> > [    2.955518]  Command = NCRd (0xc)
> > [    2.955519]  Address Type = Non-Secure DRAM
> > [    2.955521]  Address = 0x30039e80 -- 30000000.sysram + 0x39e80
> > [    2.955521]  TLimit = 0x3ff
> > [    2.955522]  Poison Error Mask = 0x80
> > [    2.955523]  More Info = 0x800
> > [    2.955524]  Timeout Info = 0x0
> > [    2.955525]          Poison Info = 0x800
> > [    2.955526]          Read Request failed GSC checks
> > [    2.955527]  Source = L2_1 (A57) (0x1)
> > [    2.955528]  TID = 0xe
> > 
> > IIUC, there was read request for 0x30039e80 from EL1/2 which failed.
> > This address falls in the sysram security aperture and hence a read
> > from normal mode failed.
> > 
> > sysram is mapped at 0x3000_0000 to 0x3004_ffff and is managed by the
> > sram driver (drivers/misc/sram.c). There are two reserved pools for
> > BPMP driver communication at 0x3004_e000 and 0x3004_f000 of 0x1000
> > bytes each.
> > 
> > sram driver maps complete 0x3000_0000 to 0x3004_ffff range as normal
> > memory.
> 
> That's your problem. It's not really worth attempting to reason about, the
> architecture says that anything mapped as Normal memory may be speculatively
> accessed at any time, so no amount of second-guessing is going to save you
> in general. Don't make stuff accessible to the kernel that it doesn't need
> to access, and especially don't make stuff accessible to the kernel if
> accessing it will kill the system.
> 
I agree and [1] was an attempt in that direction. What I wonder here is that
processor is speculating on an address range which kernel has never accessed.
Is it correct behavior that cpu is speculating in EL1/EL2 on an address
accessed in EL3?

> > However, only the BPMP reserved pools (0x3004_e000 - 0x3004_ffff)
> > are accessible from the kernel. Address 0x3003_9e80 is inaccessible
> > from the kernel and a read to it (which I believe is speculative)
> > causes the SError. Only driver which uses sysram is not initialized at
> > this point (rootfs_initcall level). As since
> > commit d70f5e541ab3 ("firmware: tegra: Make BPMP a regular driver")
> > bpmp driver is initialized at device_initcall level.
> > 
> > If none of the drivers on the kernel side using 0x3003_9e80 address
> > range. Why a read to it occurs even speculatively? Could it be that
> > some EL3 software didn’t cleanup after itself properly? Any
> > suggestions on debugging this issue further?
> > 
> > Another solution suggested in [1] was to add no-memory-wc in sysram
> > node in device-tree so that sysram is mapped as device-memory. Thus
> > preventing any speculative access. However, it causes another set of
> > issues with the bpmp driver. That's may be a discussion for another
> > time.
> 
> AFAICS the truly correct solution is what Stephen initially suggested there
> - for the boot process to somehow describe which parts of SRAM have been
> reserved by Secure software and/or which parts remain Non-Secure, and for
> the kernel driver to only map and use the latter.
Yes, let me see what I can do.
> 
> Robin.

Thanks,
Yousaf

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