On 23/02/2021 14:18, Marc Zyngier wrote: > Hi Guillaume, > > On Tue, 23 Feb 2021 09:46:30 +0000, > Guillaume Tucker <[email protected]> wrote: >> >> Hello Marc, >> >> Please see the bisection report below about a boot failure on >> meson-sm1-khadas-vim3l on mainline. It seems to only be >> affecting kernels built with CONFIG_ARM64_64K_PAGES=y. >> >> Reports aren't automatically sent to the public while we're >> trialing new bisection features on kernelci.org but this one >> looks valid. >> >> There's no output in the log, so the kernel is most likely >> crashing early. Some more details can be found here: >> >> https://kernelci.org/test/case/id/6034bed3b344e2860daddcc8/ >> >> Please let us know if you need any help to debug the issue or try >> a fix on this platform. > > Thanks for the heads up. > > There is actually a fundamental problem with the patch you bisected > to: it provides no guarantee that the point where we enable the EL2 > MMU is in the idmap and, as it turns out, the code we're running from > disappears from under our feet, leading to a translation fault we're > not prepared to handle. > > How does it work with 4kB pages? Luck.
There may be a fascinating explanation for it, but luck works too. It really seems to be booting happily with 4k pages: https://kernelci.org/test/plan/id/60347b358de339d1b7addcc5/ > Do you mind giving the patch below a go? It does work on my vim3l and > on a FVP, so odds are that it will solve it for you too. Sure, and that worked here as well: http://lava.baylibre.com:10080/scheduler/job/752416 and here's the test branch where I applied your fix, for completeness: https://gitlab.collabora.com/gtucker/linux/-/commits/v5.11-vim3l-vhe/ As always, if you do send a patch with the fix, please give some credit to the bot: Reported-by: "kernelci.org bot" <[email protected]> Thanks, Guillaume > Thanks, > > M. > > diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S > index 678cd2c618ee..fbd2543b8f7d 100644 > --- a/arch/arm64/kernel/hyp-stub.S > +++ b/arch/arm64/kernel/hyp-stub.S > @@ -96,8 +96,10 @@ SYM_CODE_START_LOCAL(mutate_to_vhe) > cmp x1, xzr > and x2, x2, x1 > csinv x2, x2, xzr, ne > - cbz x2, 1f > + cbnz x2, 2f > > +1: eret > +2: > // Engage the VHE magic! > mov_q x0, HCR_HOST_VHE_FLAGS > msr hcr_el2, x0 > @@ -131,11 +133,29 @@ SYM_CODE_START_LOCAL(mutate_to_vhe) > msr mair_el1, x0 > isb > > + // Hack the exception return to stay at EL2 > + mrs x0, spsr_el1 > + and x0, x0, #~PSR_MODE_MASK > + mov x1, #PSR_MODE_EL2h > + orr x0, x0, x1 > + msr spsr_el1, x0 > + > + b enter_vhe > +SYM_CODE_END(mutate_to_vhe) > + > + // At the point where we reach enter_vhe(), we run with > + // the MMU off (which is enforced by mutate_to_vhe()). > + // We thus need to be in the idmap, or everything will > + // explode when enabling the MMU. > + > + .pushsection .idmap.text, "ax" > + > +SYM_CODE_START_LOCAL(enter_vhe) > + // Enable the EL2 S1 MMU, as set up from EL1 > // Invalidate TLBs before enabling the MMU > tlbi vmalle1 > dsb nsh > > - // Enable the EL2 S1 MMU, as set up from EL1 > mrs_s x0, SYS_SCTLR_EL12 > set_sctlr_el1 x0 > > @@ -143,17 +163,12 @@ SYM_CODE_START_LOCAL(mutate_to_vhe) > mov_q x0, INIT_SCTLR_EL1_MMU_OFF > msr_s SYS_SCTLR_EL12, x0 > > - // Hack the exception return to stay at EL2 > - mrs x0, spsr_el1 > - and x0, x0, #~PSR_MODE_MASK > - mov x1, #PSR_MODE_EL2h > - orr x0, x0, x1 > - msr spsr_el1, x0 > - > mov x0, xzr > > -1: eret > -SYM_CODE_END(mutate_to_vhe) > + eret > +SYM_CODE_END(enter_vhe) > + > + .popsection > > .macro invalid_vector label > SYM_CODE_START_LOCAL(\label) > >
