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Message-ID: <20191014045139.GN4080@umbus.fritz.box>
Date: Mon, 14 Oct 2019 15:51:39 +1100
From: David Gibson <david@...son.dropbear.id.au>
To: Ram Pai <linuxram@...ibm.com>
Cc: linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
linuxppc-dev@...ts.ozlabs.org,
virtualization@...ts.linux-foundation.org,
benh@...nel.crashing.org, mpe@...erman.id.au, paulus@...abs.org,
mdroth@...ux.vnet.ibm.com, aik@...ux.ibm.com, paul.burton@...s.com,
robin.murphy@....com, b.zolnierkie@...sung.com,
m.szyprowski@...sung.com, hch@....de, jasowang@...hat.com,
andmike@...ibm.com, sukadev@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/2] dma-mapping: Add dma_addr_is_phys_addr()
On Fri, Oct 11, 2019 at 06:25:18PM -0700, Ram Pai wrote:
> From: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
>
> In order to safely use the DMA API, virtio needs to know whether DMA
> addresses are in fact physical addresses and for that purpose,
> dma_addr_is_phys_addr() is introduced.
>
> cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> cc: David Gibson <david@...son.dropbear.id.au>
> cc: Michael Ellerman <mpe@...erman.id.au>
> cc: Paul Mackerras <paulus@...abs.org>
> cc: Michael Roth <mdroth@...ux.vnet.ibm.com>
> cc: Alexey Kardashevskiy <aik@...ux.ibm.com>
> cc: Paul Burton <paul.burton@...s.com>
> cc: Robin Murphy <robin.murphy@....com>
> cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
> cc: Marek Szyprowski <m.szyprowski@...sung.com>
> cc: Christoph Hellwig <hch@....de>
> Suggested-by: Michael S. Tsirkin <mst@...hat.com>
> Signed-off-by: Ram Pai <linuxram@...ibm.com>
> Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
The change itself looks ok, so
Reviewed-by: David Gibson <david@...son.dropbear.id.au>
However, I would like to see the commit message (and maybe the inline
comments) expanded a bit on what the distinction here is about. Some
of the text from the next patch would be suitable, about DMA addresses
usually being in a different address space but not in the case of
bounce buffering.
> ---
> arch/powerpc/include/asm/dma-mapping.h | 21 +++++++++++++++++++++
> arch/powerpc/platforms/pseries/Kconfig | 1 +
> include/linux/dma-mapping.h | 20 ++++++++++++++++++++
> kernel/dma/Kconfig | 3 +++
> 4 files changed, 45 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h
> index 565d6f7..f92c0a4b 100644
> --- a/arch/powerpc/include/asm/dma-mapping.h
> +++ b/arch/powerpc/include/asm/dma-mapping.h
> @@ -5,6 +5,8 @@
> #ifndef _ASM_DMA_MAPPING_H
> #define _ASM_DMA_MAPPING_H
>
> +#include <asm/svm.h>
> +
> static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
> {
> /* We don't handle the NULL dev case for ISA for now. We could
> @@ -15,4 +17,23 @@ static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
> return NULL;
> }
>
> +#ifdef CONFIG_ARCH_HAS_DMA_ADDR_IS_PHYS_ADDR
> +/**
> + * dma_addr_is_phys_addr - check whether a device DMA address is a physical
> + * address
> + * @dev: device to check
> + *
> + * Returns %true if any DMA address for this device happens to also be a valid
> + * physical address (not necessarily of the same page).
> + */
> +static inline bool dma_addr_is_phys_addr(struct device *dev)
> +{
> + /*
> + * Secure guests always use the SWIOTLB, therefore DMA addresses are
> + * actually the physical address of the bounce buffer.
> + */
> + return is_secure_guest();
> +}
> +#endif
> +
> #endif /* _ASM_DMA_MAPPING_H */
> diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
> index 9e35cdd..0108150 100644
> --- a/arch/powerpc/platforms/pseries/Kconfig
> +++ b/arch/powerpc/platforms/pseries/Kconfig
> @@ -152,6 +152,7 @@ config PPC_SVM
> select SWIOTLB
> select ARCH_HAS_MEM_ENCRYPT
> select ARCH_HAS_FORCE_DMA_UNENCRYPTED
> + select ARCH_HAS_DMA_ADDR_IS_PHYS_ADDR
> help
> There are certain POWER platforms which support secure guests using
> the Protected Execution Facility, with the help of an Ultravisor
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index f7d1eea..6df5664 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -693,6 +693,26 @@ static inline bool dma_addressing_limited(struct device *dev)
> dma_get_required_mask(dev);
> }
>
> +#ifndef CONFIG_ARCH_HAS_DMA_ADDR_IS_PHYS_ADDR
> +/**
> + * dma_addr_is_phys_addr - check whether a device DMA address is a physical
> + * address
> + * @dev: device to check
> + *
> + * Returns %true if any DMA address for this device happens to also be a valid
> + * physical address (not necessarily of the same page).
> + */
> +static inline bool dma_addr_is_phys_addr(struct device *dev)
> +{
> + /*
> + * Except in very specific setups, DMA addresses exist in a different
> + * address space from CPU physical addresses and cannot be directly used
> + * to reference system memory.
> + */
> + return false;
> +}
> +#endif
> +
> #ifdef CONFIG_ARCH_HAS_SETUP_DMA_OPS
> void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> const struct iommu_ops *iommu, bool coherent);
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index 9decbba..6209b46 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -51,6 +51,9 @@ config ARCH_HAS_DMA_MMAP_PGPROT
> config ARCH_HAS_FORCE_DMA_UNENCRYPTED
> bool
>
> +config ARCH_HAS_DMA_ADDR_IS_PHYS_ADDR
> + bool
> +
> config DMA_NONCOHERENT_CACHE_SYNC
> bool
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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