Re: ARM64: Regression with commit e3067861ba66 ("arm64: add basic VMAP_STACK support")

[Mark Rutland]

On Mon, Oct 16, 2017 at 03:12:45PM +0100, Robin Murphy wrote:
> On 16/10/17 14:48, Mark Rutland wrote:
> > Hi Leo,
> > 
> > On Mon, Oct 16, 2017 at 09:17:23AM +0800, Leo Yan wrote:
> >> On Tue, Oct 10, 2017 at 05:03:44PM +0100, Robin Murphy wrote:
> >>> On 10/10/17 16:45, Mark Rutland wrote:
> >>>> On Tue, Oct 10, 2017 at 10:27:25PM +0800, Leo Yan wrote:
> >>>>> I work mainline kernel on Hikey620 board, I find it's easily to
> >>>>> introduce the panic and report the log as below. So I bisect the kernel
> >>>>> and finally narrow down the commit e3067861ba66 ("arm64: add basic
> >>>>> VMAP_STACK support") which introduce this issue.
> >>>>>
> >>>>> I tried to remove 'select HAVE_ARCH_VMAP_STACK' from
> >>>>> arch/arm64/Kconfig, then I can see the panic issue will dismiss. So
> >>>>> could you check this and have insight for this issue?
> >>>>
> >>>> Given the stuff in the backtrace, my suspicion is something is trying to
> >>>> perform DMA to/from the stack, getting junk addresses form the attempted
> >>>> virt<->phys conversions.
> >>>>
> >>>> Could you try enabling both VMAP_STACK and CONFIG_DEBUG_VIRTUAL?
> >>>
> >>> CONFIG_DMA_API_DEBUG should scream about drivers trying to use stack
> >>> addresses either way, too.
> >>
> >> Thanks for suggestions, Mark & Robin.
> >>
> >> I enabled these debugging configs but cannot get clue from it; but
> >> occasionally found this issue is quite likely related with CA53 errata,
> >> especialy ERRATA_A53_855873 is the relative one. So I changed to use
> >> ARM-TF mainline code with ERRATA fixing, this issue can be dismissed.
> > 
> > Thanks for the update.
> > 
> > Just to confirm, with the updated firmware you no longer see the issue?
> > 
> > I can't immediately see how that would be related.
> 
> Cores up to r0p2 have the other errata to which
> ARM64_WORKAROUND_CLEAN_CACHE also applies anyway; r3p0+ have an ACTLR
> bit to do thee CVAC->CIVAC upgrade in hardware, and our policy is that
> we expect firmware to enable such hardware workarounds where possible. I
> assume that's why we don't explicitly document 855873 anywhere in Linux.

Sure, I also looked it up. ;)

I meant that I couldn't immediately see why VMAP'd stacks were likely to
tickle issues with that more reliably.

Thanks,
Mark.