[ +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@xxxxxxx> --- 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@xxxxxxxxxxxxxx/#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)
