[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen master] xen: introduce an arch helper for default dma zone status
commit 15e64b8a099eb9d37485fdc2046ac769cc6a1628 Author: Wei Chen <wei.chen@xxxxxxx> AuthorDate: Fri Jun 10 13:53:11 2022 +0800 Commit: Julien Grall <jgrall@xxxxxxxxxx> CommitDate: Fri Jun 17 09:36:12 2022 +0100 xen: introduce an arch helper for default dma zone status In current code, when Xen is running in a multiple nodes NUMA system, it will set dma_bitsize in end_boot_allocator to reserve some low address memory as DMA zone. There are some x86 implications in the implementation. Because on x86, memory starts from 0. On a multiple-nodes NUMA system, if a single node contains the majority or all of the DMA memory, x86 prefers to give out memory from non-local allocations rather than exhausting the DMA memory ranges. Hence x86 uses dma_bitsize to set aside some largely arbitrary amount of memory for DMA zone. The allocations from DMA zone would happen only after exhausting all other nodes' memory. But the implications are not shared across all architectures. For example, Arm cannot guarantee the availability of memory below a certain boundary for DMA limited-capability devices either. But currently, Arm doesn't need a reserved DMA zone in Xen. Because there is no DMA device in Xen. And for guests, Xen Arm only allows Dom0 to have DMA operations without IOMMU. Xen will try to allocate memory under 4GB or memory range that is limited by dma_bitsize for Dom0 in boot time. For DomU, even Xen can passthrough devices to DomU without IOMMU, but Xen Arm doesn't guarantee their DMA operations. So, Xen Arm doesn't need a reserved DMA zone to provide DMA memory for guests. In this patch, we introduce an arch_want_default_dmazone helper for different architectures to determine whether they need to set dma_bitsize for DMA zone reservation or not. At the same time, when x86 Xen is built with CONFIG_PV=n could probably leverage this new helper to actually not trigger DMA zone reservation. Signed-off-by: Wei Chen <wei.chen@xxxxxxx> Tested-by: Jiamei Xie <jiamei.xie@xxxxxxx> Acked-by: Jan Beulich <jbeulich@xxxxxxxx> --- xen/arch/arm/include/asm/numa.h | 1 + xen/arch/x86/include/asm/numa.h | 1 + xen/common/page_alloc.c | 2 +- 3 files changed, 3 insertions(+), 1 deletion(-) diff --git a/xen/arch/arm/include/asm/numa.h b/xen/arch/arm/include/asm/numa.h index 31a6de4e23..e4c4d89192 100644 --- a/xen/arch/arm/include/asm/numa.h +++ b/xen/arch/arm/include/asm/numa.h @@ -24,6 +24,7 @@ extern mfn_t first_valid_mfn; #define node_spanned_pages(nid) (max_page - mfn_x(first_valid_mfn)) #define node_start_pfn(nid) (mfn_x(first_valid_mfn)) #define __node_distance(a, b) (20) +#define arch_want_default_dmazone() (false) #endif /* __ARCH_ARM_NUMA_H */ /* diff --git a/xen/arch/x86/include/asm/numa.h b/xen/arch/x86/include/asm/numa.h index bada2c0bb9..5d8385f2e1 100644 --- a/xen/arch/x86/include/asm/numa.h +++ b/xen/arch/x86/include/asm/numa.h @@ -74,6 +74,7 @@ static inline __attribute__((pure)) nodeid_t phys_to_nid(paddr_t addr) #define node_spanned_pages(nid) (NODE_DATA(nid)->node_spanned_pages) #define node_end_pfn(nid) (NODE_DATA(nid)->node_start_pfn + \ NODE_DATA(nid)->node_spanned_pages) +#define arch_want_default_dmazone() (num_online_nodes() > 1) extern int valid_numa_range(u64 start, u64 end, nodeid_t node); diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c index ea59cd1a4a..000ae6b972 100644 --- a/xen/common/page_alloc.c +++ b/xen/common/page_alloc.c @@ -1889,7 +1889,7 @@ void __init end_boot_allocator(void) } nr_bootmem_regions = 0; - if ( !dma_bitsize && (num_online_nodes() > 1) ) + if ( !dma_bitsize && arch_want_default_dmazone() ) dma_bitsize = arch_get_dma_bitsize(); printk("Domain heap initialised"); -- generated by git-patchbot for /home/xen/git/xen.git#master
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