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SubjectRe: framebuffer corruption due to overlapping stp instructions on arm64
Ard, Mikulas,

pon., 6 sie 2018 o 22:11 Ard Biesheuvel <ard.biesheuvel@linaro.org> napisał(a):
>
> On 6 August 2018 at 21:54, Mikulas Patocka <mpatocka@redhat.com> wrote:
> >
> >
> > On Mon, 6 Aug 2018, Ard Biesheuvel wrote:
> >
> >> On 6 August 2018 at 19:09, Mikulas Patocka <mpatocka@redhat.com> wrote:
> >> >
> >> >
> >> > On Mon, 6 Aug 2018, Ard Biesheuvel wrote:
> >> >
> >> >> On 6 August 2018 at 14:42, Robin Murphy <robin.murphy@arm.com> wrote:
> >> >> > On 06/08/18 11:25, Mikulas Patocka wrote:
> >> >> > [...]
> >> >> >>>
> >> >> >>> None of this explains why some transactions fail to make it across
> >> >> >>> entirely. The overlapping writes in question write the same data to
> >> >> >>> the memory locations that are covered by both, and so the ordering in
> >> >> >>> which the transactions are received should not affect the outcome.
> >> >> >>
> >> >> >>
> >> >> >> You're right that the corruption couldn't be explained just by reordering
> >> >> >> writes. My hypothesis is that the PCIe controller tries to disambiguate
> >> >> >> the overlapping writes, but the disambiguation logic was not tested and it
> >> >> >> is buggy. If there's a barrier between the overlapping writes, the PCIe
> >> >> >> controller won't see any overlapping writes, so it won't trigger the
> >> >> >> faulty disambiguation logic and it works.
> >> >> >>
> >> >> >> Could the ARM engineers look if there's some chicken bit in Cortex-A72
> >> >> >> that could insert barriers between non-cached writes automatically?
> >> >> >
> >> >> >
> >> >> > I don't think there is, and even if there was I imagine it would have a
> >> >> > pretty hideous effect on non-coherent DMA buffers and the various other
> >> >> > places in which we have Normal-NC mappings of actual system RAM.
> >> >> >
> >> >>
> >> >> Looking at the A72 manual, there is one chicken bit that looks like it
> >> >> may be related:
> >> >>
> >> >> CPUACTLR_EL1 bit #50:
> >> >>
> >> >> 0 Enables store streaming on NC/GRE memory type. This is the reset value.
> >> >> 1 Disables store streaming on NC/GRE memory type.
> >> >>
> >> >> so putting something like
> >> >>
> >> >> mrs x0, S3_1_C15_C2_0
> >> >> orr x0, x0, #(1 << 50)
> >> >> msr S3_1_C15_C2_0, x0
> >> >>
> >> >> in __cpu_setup() would be worth a try.
> >> >
> >> > It won't boot.
> >> >
> >> > But if i write the same value that was read, it also won't boot.
> >> >
> >> > I created a simple kernel module that reads this register and it has bit
> >> > 32 set, all other bits clear. But when I write the same value into it, the
> >> > core that does the write is stuck in infinite loop.
> >> >
> >> > So, it seems that we are writing this register from a wrong place.
> >> >
> >>
> >> Ah, my bad. I didn't look closely enough at the description:
> >>
> >> """
> >> The accessibility to the CPUACTLR_EL1 by Exception level is:
> >>
> >> EL0 -
> >> EL1(NS) RW (a)
> >> EL1(S) RW (a)
> >> EL2 RW (b)
> >> EL3(SCR.NS = 1) RW
> >> EL3(SCR.NS = 0) RW
> >>
> >> (a) Write access if ACTLR_EL3.CPUACTLR is 1 and ACTLR_EL2.CPUACTLR is
> >> 1, or ACTLR_EL3.CPUACTLR is 1 and SCR.NS is 0.
> >> """
> >>
> >> so you'll have to do this from ARM Trusted Firmware. If you're
> >> comfortable rebuilding that:
> >>
> >> diff --git a/include/lib/cpus/aarch64/cortex_a72.h
> >> b/include/lib/cpus/aarch64/cortex_a72.h
> >> index bfd64918625b..a7b8cf4be0c6 100644
> >> --- a/include/lib/cpus/aarch64/cortex_a72.h
> >> +++ b/include/lib/cpus/aarch64/cortex_a72.h
> >> @@ -31,6 +31,7 @@
> >> #define CORTEX_A72_ACTLR_EL1 S3_1_C15_C2_0
> >>
> >> #define CORTEX_A72_ACTLR_DISABLE_L1_DCACHE_HW_PFTCH (1 << 56)
> >> +#define CORTEX_A72_ACTLR_DIS_NC_GRE_STORE_STREAMING (1 << 50)
> >> #define CORTEX_A72_ACTLR_NO_ALLOC_WBWA (1 << 49)
> >> #define CORTEX_A72_ACTLR_DCC_AS_DCCI (1 << 44)
> >> #define CORTEX_A72_ACTLR_EL1_DIS_INSTR_PREFETCH (1 << 32)
> >> diff --git a/lib/cpus/aarch64/cortex_a72.S b/lib/cpus/aarch64/cortex_a72.S
> >> index 55e508678284..5914d6ee3ba6 100644
> >> --- a/lib/cpus/aarch64/cortex_a72.S
> >> +++ b/lib/cpus/aarch64/cortex_a72.S
> >> @@ -133,6 +133,15 @@ func cortex_a72_reset_func
> >> orr x0, x0, #CORTEX_A72_ECTLR_SMP_BIT
> >> msr CORTEX_A72_ECTLR_EL1, x0
> >> isb
> >> +
> >> + /* ---------------------------------------------
> >> + * Disables store streaming on NC/GRE memory type.
> >> + * ---------------------------------------------
> >> + */
> >> + mrs x0, CORTEX_A72_ACTLR_EL1
> >> + orr x0, x0, #CORTEX_A72_ACTLR_DIS_NC_GRE_STORE_STREAMING
> >> + msr CORTEX_A72_ACTLR_EL1, x0
> >> + isb
> >> ret x19
> >> endfunc cortex_a72_reset_func
> >
> > Unfortunatelly, it doesn't work. I verified that the bit is set after
> > booting Linux, but the memcpy corruption was still present.
> >
> > I also tried the other chicken bits, it slowed down the system noticeably,
> > but had no effect on the memcpy corruption.
> >
>
> OK, it was worth a shot
>
> Let's wait and see if Marcin has any results.
>

After some self-caused setup issues I was able to run the test on my
MacchiatoBin with the kernel v4.18-rc8. It's been running for 1h+ now,
loading the CPU to 100% and no single error event...

I built the binary file with:
gcc-linaro-7.2.1-2017.11-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc -O2

Maybe it's the older firmware issue? Please send the full bootlog with
the very first line after reset. My board rev is v1.3 and I use
mainline UEFI (newest edk2 + edk2-platforms) + newest publicly
available ARM-TF and earliest firmware for this board.

Best regards,
Marcin

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