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Message-ID: <mhng-9c1955e1-d7cf-4ee4-8bf8-6bef720c9b98@palmer-si-x1c4>
Date: Fri, 16 Nov 2018 08:52:14 -0800 (PST)
From: Palmer Dabbelt <palmer@...ive.com>
To: Christoph Hellwig <hch@....de>
CC: iommu@...ts.linux-foundation.org, linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] arch: switch the default on ARCH_HAS_SG_CHAIN
On Fri, 09 Nov 2018 01:00:08 PST (-0800), Christoph Hellwig wrote:
> These days architectures are mostly out of the business of dealing with
> struct scatterlist at all, unless they have architecture specific iommu
> drivers. Replace the ARCH_HAS_SG_CHAIN symbol with a ARCH_NO_SG_CHAIN
> one only enabled for architectures with horrible legacy iommu drivers
> like alpha and parisc, and conditionally for arm which wants to keep it
> disable for legacy platforms.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
> .../features/io/sg-chain/arch-support.txt | 33 -------------------
> arch/alpha/Kconfig | 1 +
> arch/arc/Kconfig | 1 -
> arch/arm/Kconfig | 2 +-
> arch/arm64/Kconfig | 1 -
> arch/ia64/Kconfig | 1 -
> arch/parisc/Kconfig | 1 +
> arch/powerpc/Kconfig | 1 -
> arch/s390/Kconfig | 1 -
> arch/sparc/Kconfig | 1 -
> arch/x86/Kconfig | 1 -
> arch/xtensa/Kconfig | 1 -
> include/linux/scatterlist.h | 6 ++--
> lib/Kconfig | 2 +-
> lib/scatterlist.c | 2 +-
> 15 files changed, 8 insertions(+), 47 deletions(-)
> delete mode 100644 Documentation/features/io/sg-chain/arch-support.txt
As far as I can tell, it looks like m68k, mips, and powerpc mention an IOMMU in
their ports, don't set ARCH_HAS_SG_CHAIN, and with this patch set won't set
ARCH_NO_SG_CHAIN. The issue is that I'm not sure how to determine what
constitutes a horrible legacy IOMMU, at least with respect to not being able to
use scatterlist chaining.
I poked through the 68k stuff (sun3 and sun3x) and the only thing I see that's
odd is that DVMA_PAGE_SHIFT is 13. That matches PAGE_SHIFT for the subarch,
though, so I don't think it's an issue. It looks like the mention in MIPS is
trivial, so that should be fine. There's a lot in the PC port so I just
glanced at it. I assume it's OK, but I did see an explicit mention of SG in
their generic IOMMU. There's a lot of flavors here so I'm not sure how well
they all work.
I don't really think that's enough for my reviewed-by tag, so feel free to give
me some pointers if you're looking for one -- I'd be happy to lean about
IOMMUs (particularly broken ones, as that might help prevent us from designing
a broken one), I'm just not sure what I'm looking for.
I'm going to assume you're going to merge this and I'll drop the RISC-V patch
that turns on ARCH_HAS_SG_CHAIN.
Thanks!
> diff --git a/Documentation/features/io/sg-chain/arch-support.txt b/Documentation/features/io/sg-chain/arch-support.txt
> deleted file mode 100644
> index 6554f0372c3f..000000000000
> --- a/Documentation/features/io/sg-chain/arch-support.txt
> +++ /dev/null
> @@ -1,33 +0,0 @@
> -#
> -# Feature name: sg-chain
> -# Kconfig: ARCH_HAS_SG_CHAIN
> -# description: arch supports chained scatter-gather lists
> -#
> - -----------------------
> - | arch |status|
> - -----------------------
> - | alpha: | TODO |
> - | arc: | ok |
> - | arm: | ok |
> - | arm64: | ok |
> - | c6x: | TODO |
> - | h8300: | TODO |
> - | hexagon: | TODO |
> - | ia64: | ok |
> - | m68k: | TODO |
> - | microblaze: | TODO |
> - | mips: | TODO |
> - | nds32: | TODO |
> - | nios2: | TODO |
> - | openrisc: | TODO |
> - | parisc: | TODO |
> - | powerpc: | ok |
> - | riscv: | TODO |
> - | s390: | ok |
> - | sh: | TODO |
> - | sparc: | ok |
> - | um: | TODO |
> - | unicore32: | TODO |
> - | x86: | ok |
> - | xtensa: | TODO |
> - -----------------------
> diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
> index 5b4f88363453..a7e748a46c18 100644
> --- a/arch/alpha/Kconfig
> +++ b/arch/alpha/Kconfig
> @@ -5,6 +5,7 @@ config ALPHA
> select ARCH_MIGHT_HAVE_PC_PARPORT
> select ARCH_MIGHT_HAVE_PC_SERIO
> select ARCH_NO_PREEMPT
> + select ARCH_NO_SG_CHAIN
> select ARCH_USE_CMPXCHG_LOCKREF
> select HAVE_AOUT
> select HAVE_IDE
> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> index c9e2a1323536..fd48d698da29 100644
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -13,7 +13,6 @@ config ARC
> select ARCH_HAS_PTE_SPECIAL
> select ARCH_HAS_SYNC_DMA_FOR_CPU
> select ARCH_HAS_SYNC_DMA_FOR_DEVICE
> - select ARCH_HAS_SG_CHAIN
> select ARCH_SUPPORTS_ATOMIC_RMW if ARC_HAS_LLSC
> select BUILDTIME_EXTABLE_SORT
> select CLONE_BACKWARDS
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 91be74d8df65..199eb62230b0 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -19,6 +19,7 @@ config ARM
> select ARCH_HAVE_CUSTOM_GPIO_H
> select ARCH_HAS_GCOV_PROFILE_ALL
> select ARCH_MIGHT_HAVE_PC_PARPORT
> + select ARCH_NO_SG_CHAIN if !ARM_HAS_SG_CHAIN
> select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
> select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
> select ARCH_SUPPORTS_ATOMIC_RMW
> @@ -118,7 +119,6 @@ config ARM
> <http://www.arm.linux.org.uk/>.
>
> config ARM_HAS_SG_CHAIN
> - select ARCH_HAS_SG_CHAIN
> bool
>
> config ARM_DMA_USE_IOMMU
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 787d7850e064..4c851b3a7b7c 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -23,7 +23,6 @@ config ARM64
> select ARCH_HAS_MEMBARRIER_SYNC_CORE
> select ARCH_HAS_PTE_SPECIAL
> select ARCH_HAS_SET_MEMORY
> - select ARCH_HAS_SG_CHAIN
> select ARCH_HAS_STRICT_KERNEL_RWX
> select ARCH_HAS_STRICT_MODULE_RWX
> select ARCH_HAS_SYNC_DMA_FOR_DEVICE
> diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
> index 36773def6920..d6f203658994 100644
> --- a/arch/ia64/Kconfig
> +++ b/arch/ia64/Kconfig
> @@ -29,7 +29,6 @@ config IA64
> select HAVE_MEMBLOCK_NODE_MAP
> select HAVE_VIRT_CPU_ACCOUNTING
> select ARCH_HAS_DMA_MARK_CLEAN
> - select ARCH_HAS_SG_CHAIN
> select VIRT_TO_BUS
> select ARCH_DISCARD_MEMBLOCK
> select GENERIC_IRQ_PROBE
> diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
> index 92a339ee28b3..428ee50fc3db 100644
> --- a/arch/parisc/Kconfig
> +++ b/arch/parisc/Kconfig
> @@ -11,6 +11,7 @@ config PARISC
> select ARCH_HAS_ELF_RANDOMIZE
> select ARCH_HAS_STRICT_KERNEL_RWX
> select ARCH_HAS_UBSAN_SANITIZE_ALL
> + select ARCH_NO_SG_CHAIN
> select ARCH_SUPPORTS_MEMORY_FAILURE
> select RTC_CLASS
> select RTC_DRV_GENERIC
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 8be31261aec8..4bc8edd83cee 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -138,7 +138,6 @@ config PPC
> select ARCH_HAS_PTE_SPECIAL
> select ARCH_HAS_MEMBARRIER_CALLBACKS
> select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE && PPC64
> - select ARCH_HAS_SG_CHAIN
> select ARCH_HAS_STRICT_KERNEL_RWX if ((PPC_BOOK3S_64 || PPC32) && !RELOCATABLE && !HIBERNATION)
> select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> select ARCH_HAS_UACCESS_FLUSHCACHE if PPC64
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 5173366af8f3..5624e8607054 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -73,7 +73,6 @@ config S390
> select ARCH_HAS_KCOV
> select ARCH_HAS_PTE_SPECIAL
> select ARCH_HAS_SET_MEMORY
> - select ARCH_HAS_SG_CHAIN
> select ARCH_HAS_STRICT_KERNEL_RWX
> select ARCH_HAS_STRICT_MODULE_RWX
> select ARCH_HAS_UBSAN_SANITIZE_ALL
> diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
> index 490b2c95c212..8853b6ceae17 100644
> --- a/arch/sparc/Kconfig
> +++ b/arch/sparc/Kconfig
> @@ -40,7 +40,6 @@ config SPARC
> select MODULES_USE_ELF_RELA
> select ODD_RT_SIGACTION
> select OLD_SIGSUSPEND
> - select ARCH_HAS_SG_CHAIN
> select CPU_NO_EFFICIENT_FFS
> select LOCKDEP_SMALL if LOCKDEP
> select NEED_DMA_MAP_STATE
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index ba7e3464ee92..6faab6f9b57e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -66,7 +66,6 @@ config X86
> select ARCH_HAS_UACCESS_FLUSHCACHE if X86_64
> select ARCH_HAS_UACCESS_MCSAFE if X86_64 && X86_MCE
> select ARCH_HAS_SET_MEMORY
> - select ARCH_HAS_SG_CHAIN
> select ARCH_HAS_STRICT_KERNEL_RWX
> select ARCH_HAS_STRICT_MODULE_RWX
> select ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
> diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
> index d29b7365da8d..e3387919eb22 100644
> --- a/arch/xtensa/Kconfig
> +++ b/arch/xtensa/Kconfig
> @@ -1,7 +1,6 @@
> # SPDX-License-Identifier: GPL-2.0
> config XTENSA
> def_bool y
> - select ARCH_HAS_SG_CHAIN
> select ARCH_HAS_SYNC_DMA_FOR_CPU
> select ARCH_HAS_SYNC_DMA_FOR_DEVICE
> select ARCH_NO_COHERENT_DMA_MMAP if !MMU
> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
> index 093aa57120b0..b96f0d0b5b8f 100644
> --- a/include/linux/scatterlist.h
> +++ b/include/linux/scatterlist.h
> @@ -324,10 +324,10 @@ size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
> * Like SG_CHUNK_SIZE, but for archs that have sg chaining. This limit
> * is totally arbitrary, a setting of 2048 will get you at least 8mb ios.
> */
> -#ifdef CONFIG_ARCH_HAS_SG_CHAIN
> -#define SG_MAX_SEGMENTS 2048
> -#else
> +#ifdef CONFIG_ARCH_NO_SG_CHAIN
> #define SG_MAX_SEGMENTS SG_CHUNK_SIZE
> +#else
> +#define SG_MAX_SEGMENTS 2048
> #endif
>
> #ifdef CONFIG_SG_POOL
> diff --git a/lib/Kconfig b/lib/Kconfig
> index a9965f4af4dd..d5a5e2ebf286 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -577,7 +577,7 @@ config SG_POOL
> # sg chaining option
> #
>
> -config ARCH_HAS_SG_CHAIN
> +config ARCH_NO_SG_CHAIN
> def_bool n
>
> config ARCH_HAS_PMEM_API
> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
> index 7c6096a71704..9ba349e775ef 100644
> --- a/lib/scatterlist.c
> +++ b/lib/scatterlist.c
> @@ -271,7 +271,7 @@ int __sg_alloc_table(struct sg_table *table, unsigned int nents,
>
> if (nents == 0)
> return -EINVAL;
> -#ifndef CONFIG_ARCH_HAS_SG_CHAIN
> +#ifdef CONFIG_ARCH_NO_SG_CHAIN
> if (WARN_ON_ONCE(nents > max_ents))
> return -EINVAL;
> #endif
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