Messages in this thread | | | Subject | Re: [PATCH 1/2] dma-mapping: Add dma_addr_is_phys_addr() | From | Robin Murphy <> | Date | Mon, 14 Oct 2019 11:29:24 +0100 |
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On 14/10/2019 05:51, David Gibson wrote: > On Fri, Oct 11, 2019 at 06:25:18PM -0700, Ram Pai wrote: >> From: Thiago Jung Bauermann <bauerman@linux.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@kernel.crashing.org> >> cc: David Gibson <david@gibson.dropbear.id.au> >> cc: Michael Ellerman <mpe@ellerman.id.au> >> cc: Paul Mackerras <paulus@ozlabs.org> >> cc: Michael Roth <mdroth@linux.vnet.ibm.com> >> cc: Alexey Kardashevskiy <aik@linux.ibm.com> >> cc: Paul Burton <paul.burton@mips.com> >> cc: Robin Murphy <robin.murphy@arm.com> >> cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> >> cc: Marek Szyprowski <m.szyprowski@samsung.com> >> cc: Christoph Hellwig <hch@lst.de> >> Suggested-by: Michael S. Tsirkin <mst@redhat.com> >> Signed-off-by: Ram Pai <linuxram@us.ibm.com> >> Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com> > > The change itself looks ok, so > > Reviewed-by: David Gibson <david@gibson.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.
Right, this needs a much tighter definition. "DMA address happens to be a valid physical address" is true of various IOMMU setups too, but I can't believe it's meaningful in such cases.
If what you actually want is "DMA is direct or SWIOTLB" - i.e. "DMA address is physical address of DMA data (not necessarily the original buffer)" - wouldn't dma_is_direct() suffice?
Robin.
>> --- >> 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 >> >
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