[PATCH v2] arm64: issue ISB after updating system registers

[Tom Rini]

On Wed, Jun 24, 2020 at 01:05:19AM +0000, Volodymyr Babchuk wrote:

> ARM Architecture reference manual clearly states that PE pipeline
> should be flushed after any change to system registers. Refer to
> paragraph "B2.3.5 Memory Barriers" at page B2-92 of "Arm Architecture
> Reference Manual ARMv8 for ARMv8-A Architecture Profile" (ARM DDI
> 0487B.a).
> 
> Failing to issue instruction memory synchronization barrier can lead
> to spurious errors, like synchronous exception when accessing FPU
> registers. This is very prominent on CPUs with long instruction
> pipeline, like ARM Cortex A72.
> 
> This change fixes the following U-Boot panic:
> 
>  "Synchronous Abort" handler, esr 0x1fe00000
>  elr: 00000000800948cc lr : 0000000080091e04
>  x0 : 00000000801ffdc8 x1 : 00000000000000c8
>  x2 : 00000000800979d4 x3 : 00000000801ffc60
>  x4 : 00000000801ffd40 x5 : ffffff80ffffffd8
>  x6 : 00000000801ffd70 x7 : 00000000801ffd70
>  x8 : 000000000000000a x9 : 0000000000000000
>  x10: 0000000000000044 x11: 0000000000000000
>  x12: 0000000000000000 x13: 0000000000000000
>  x14: 0000000000000000 x15: 0000000000000000
>  x16: 000000008008b2e0 x17: 0000000000000000
>  x18: 00000000801ffec0 x19: 00000000800957b0
>  x20: 00000000000000c8 x21: 00000000801ffdc8
>  x22: 000000008009909e x23: 0000000000000000
>  x24: 0000000000000000 x25: 0000000000000000
>  x26: 0000000000000000 x27: 0000000000000000
>  x28: 0000000000000000 x29: 00000000801ffc50
> 
>  Code: a94417e4 a90217e4 a9051fe6 a90617e4 (3d801fe0)
> 
> While executing instruction
> 
>  str     q0, [sp, #112]
> 
> in vsnprintf() prologue. This panic was observed only on Cortex A72 so
> far.
> 
> This patch places ISBs on other strategic places as well.
> 
> Also, this probably is the right fix for the issue workarounded in the
> commit 45f41c13 ("ARM: uniphier: add weird workaround code for LD20")
> 
> Reported-by: Oleksandr Andrushchenko <oleksandr_andrushchenko at epam.com>
> Suggested-by: Julien Grall <julien.grall.oss at gmail.com>
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk at epam.com>
> CC: Tom Rini <trini at konsulko.com>
> CC: Masahiro Yamada <yamada.masahiro at socionext.com>
> CC: Stefano Stabellini <sstabellini at kernel.org>
> Reviewed-by: Julien Grall <julien at xen.org>
> Reviewed-by: Andre Przywara <andre.przywara at arm.com>
> Tested-by: Masahiro Yamada <yamada.masahiro at socionext.com>

Applied to u-boot/master, thanks!

-- 
Tom
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