Re: [PATCH v5 0/7] arm64: Default to 32-bit wide ZONE_DMA
From: Nicolas Saenz Julienne <hidden>
Date: 2020-11-03 17:00:39
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linux-acpi, linux-devicetree, linux-iommu, linux-mm, linux-riscv, lkml
On Fri, 2020-10-30 at 18:11 +0000, Catalin Marinas wrote:
On Thu, Oct 29, 2020 at 06:25:43PM +0100, Nicolas Saenz Julienne wrote:quoted
Ard Biesheuvel (1): arm64: mm: Set ZONE_DMA size based on early IORT scan Nicolas Saenz Julienne (6): arm64: mm: Move reserve_crashkernel() into mem_init() arm64: mm: Move zone_dma_bits initialization into zone_sizes_init() of/address: Introduce of_dma_get_max_cpu_address() of: unittest: Add test for of_dma_get_max_cpu_address() arm64: mm: Set ZONE_DMA size based on devicetree's dma-ranges mm: Remove examples from enum zone_type commentThanks for putting this together. I had a minor comment but the patches look fine to me. We still need an ack from Rob on the DT patch and I can queue the series for 5.11.
I'm preparing a v6 unifying both functions as you suggested.
Could you please also test the patch below on top of this series? It's the removal of the implied DMA offset in the max_zone_phys() calculation.
Yes, happily. Comments below.
quoted hunk ↗ jump to hunk
--------------------------8<----------------------------- From 3ae252d888be4984a612236124f5b099e804c745 Mon Sep 17 00:00:00 2001 From: Catalin Marinas <catalin.marinas@arm.com> Date: Fri, 30 Oct 2020 18:07:34 +0000 Subject: [PATCH] arm64: Ignore any DMA offsets in the max_zone_phys() calculation Currently, the kernel assumes that if RAM starts above 32-bit (or zone_bits), there is still a ZONE_DMA/DMA32 at the bottom of the RAM and such constrained devices have a hardwired DMA offset. In practice, we haven't noticed any such hardware so let's assume that we can expand ZONE_DMA32 to the available memory if no RAM below 4GB. Similarly, ZONE_DMA is expanded to the 4GB limit if no RAM addressable by zone_bits. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> --- arch/arm64/mm/init.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index 095540667f0f..362160e16fb2 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c@@ -175,14 +175,21 @@ static void __init reserve_elfcorehdr(void) #endif /* CONFIG_CRASH_DUMP */ /* - * Return the maximum physical address for a zone with a given address size - * limit. It currently assumes that for memory starting above 4G, 32-bit - * devices will use a DMA offset. + * Return the maximum physical address for a zone accessible by the given bits + * limit. If the DRAM starts above 32-bit, expand the zone to the maximum + * available memory, otherwise cap it at 32-bit. */ static phys_addr_t __init max_zone_phys(unsigned int zone_bits) { - phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, zone_bits); - return min(offset + (1ULL << zone_bits), memblock_end_of_DRAM()); + phys_addr_t zone_mask = (1ULL << zone_bits) - 1;
Maybe use DMA_BIT_MASK(), instead of the manual calculation?
+ phys_addr_t phys_start = memblock_start_of_DRAM(); + + if (!(phys_start & U32_MAX))
I'd suggest using 'bigger than' instead of masks. Just to cover ourselves against memory starting at odd locations. Also it'll behaves properly when phys_start is zero (this breaks things on RPi4).
+ zone_mask = PHYS_ADDR_MAX; + else if (!(phys_start & zone_mask)) + zone_mask = U32_MAX; + + return min(zone_mask + 1, memblock_end_of_DRAM());
This + 1 isn't going to play well when zone_mask is PHYS_ADDR_MAX. Regards, Nicolas