Messages in this thread | | | Subject | Re: [PATCH] irqchip/gic-v3-its: Add early memory allocation errata | From | Matthias Brugger <> | Date | Fri, 5 Oct 2018 16:13:48 +0200 |
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On 05/10/2018 15:42, Marc Zyngier wrote: > On 05/10/18 13:33, Matthias Brugger wrote: >> >> >> On 05/10/2018 12:55, Marc Zyngier wrote: >>> Hi Matthias, >>> >>> On 04/10/18 23:11, Matthias Brugger wrote: >>>> Friendly reminder, if anyone has any comment on the patch :) >>>> >>>> On 9/12/18 11:52 AM, matthias.bgg@kernel.org wrote: >>>>> From: Matthias Brugger <mbrugger@suse.com> >>>>> >>>>> Some hardware does not implement two-level page tables so that >>>>> the amount of contigious memory needed by the baser is bigger >>>>> then the zone order. This is a known problem on Cavium Thunderx >>>>> with 4K page size. >>>>> >>>>> We fix this by adding an errata which allocates the memory early >>>>> in the boot cycle, using the memblock allocator. >>>>> >>>>> Signed-off-by: Matthias Brugger <mbrugger@suse.com> >>>>> --- >>>>> arch/arm64/Kconfig | 12 ++++++++ >>>>> arch/arm64/include/asm/cpucaps.h | 3 +- >>>>> arch/arm64/kernel/cpu_errata.c | 33 +++++++++++++++++++++ >>>>> drivers/irqchip/irq-gic-v3-its.c | 50 ++++++++++++++++++++------------ >>>>> 4 files changed, 79 insertions(+), 19 deletions(-) >>> >>> My only comment would be to state how much I dislike both the HW and the >>> patch... ;-) The idea that we have some erratum that depends on the page size >>> doesn't feel good at all. >>> >> >> Well ugly HW needs ugly patches ;-) >> >>>>> >>>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >>>>> index 1b1a0e95c751..dfd9fe08f0b2 100644 >>>>> --- a/arch/arm64/Kconfig >>>>> +++ b/arch/arm64/Kconfig >>>>> @@ -597,6 +597,18 @@ config QCOM_FALKOR_ERRATUM_E1041 >>>>> If unsure, say Y. >>>>> +config CAVIUM_ALLOC_ITS_TABLE_EARLY >>>>> + bool "Cavium Thunderx: Allocate the its table early" >>>>> + default y >>>>> + depends on ARM64_4K_PAGES && FORCE_MAX_ZONEORDER < 13 >>> >>> Here's a though: Why don't we ensure that FORCE_MAX_ZONEORDER is such as we >>> could always allocate the same amount of memory, no matter what the page size >>> is? That, or bump FORCE_MAX_ZONEORDER to 13 if the kernel includes support >>> for TX1. >>> >> >> Bumping FORCE_MAX_ZONEORDER when TX1 is supported was proposed here: >> https://patchwork.kernel.org/patch/6322281/ >> >> To bring in some more history, the CMA approach ended with this discussion: >> https://patchwork.kernel.org/patch/9888041/ >> >>> Any of this of course requires buy-in from the arm64 maintainers, as this is >>> quite a departure from the way things work so far. >>> >> >> With my distribution head on, I would prefer a solution that does not change >> FORCE_MAX_ZONEORDER. That's how I came to the idea providing a third solution to >> the same problem :) > > Why is that a problem? What impact does this have on your favourite distro? >
The impact is on changing FORCE_MAX_ZONEORDER on an already released kernel will break Kernel ABI and with that all external modules. I know that's nothing upstream cares too much about, but the distros do :)
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