Messages in this thread | | | Subject | Re: [PATCH 6/6] arm64/mm: Enable ZONE_DEVICE | From | Robin Murphy <> | Date | Wed, 3 Apr 2019 14:58:28 +0100 |
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[ +Dan, Jerome ]
On 03/04/2019 05:30, Anshuman Khandual wrote: > Arch implementation for functions which create or destroy vmemmap mapping > (vmemmap_populate, vmemmap_free) can comprehend and allocate from inside > device memory range through driver provided vmem_altmap structure which > fulfils all requirements to enable ZONE_DEVICE on the platform. Hence just
ZONE_DEVICE is about more than just altmap support, no?
> enable ZONE_DEVICE by subscribing to ARCH_HAS_ZONE_DEVICE. But this is only > applicable for ARM64_4K_PAGES (ARM64_SWAPPER_USES_SECTION_MAPS) only which > creates vmemmap section mappings and utilize vmem_altmap structure.
What prevents it from working with other page sizes? One of the foremost use-cases for our 52-bit VA/PA support is to enable mapping large quantities of persistent memory, so we really do need this for 64K pages too. FWIW, it appears not to be an issue for PowerPC.
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > --- > arch/arm64/Kconfig | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index db3e625..b5d8cf5 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -31,6 +31,7 @@ config ARM64 > select ARCH_HAS_SYSCALL_WRAPPER > select ARCH_HAS_TEARDOWN_DMA_OPS if IOMMU_SUPPORT > select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST > + select ARCH_HAS_ZONE_DEVICE if ARM64_4K_PAGES
IIRC certain configurations (HMM?) don't even build if you just turn this on alone (although of course things may have changed elsewhere in the meantime) - crucially, though, from previous discussions[1] it seems fundamentally unsafe, since I don't think we can guarantee that nobody will touch the corners of ZONE_DEVICE that also require pte_devmap in order not to go subtly wrong. I did get as far as cooking up some patches to sort that out [2][3] which I never got round to posting for their own sake, so please consider picking those up as part of this series.
Robin.
> select ARCH_HAVE_NMI_SAFE_CMPXCHG > select ARCH_INLINE_READ_LOCK if !PREEMPT > select ARCH_INLINE_READ_LOCK_BH if !PREEMPT >
[1] https://lore.kernel.org/linux-mm/CAA9_cmfA9GS+1M1aSyv1ty5jKY3iho3CERhnRAruWJW3PfmpgA@mail.gmail.com/#t [2] http://linux-arm.org/git?p=linux-rm.git;a=commitdiff;h=61816b833afdb56b49c2e58f5289ae18809e5d67 [3] http://linux-arm.org/git?p=linux-rm.git;a=commitdiff;h=a5a16560eb1becf9a1d4cc0d03d6b5e76da4f4e1 (apologies to anyone if the linux-arm.org server is being flaky as usual and requires a few tries to respond properly)
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