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    Subject[RFC PATCH 3/3] x86: Create dma_mark_dirty to dirty pages used for DMA by VM guest
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    This patch is meant to provide the guest with a way of flagging DMA pages
    as being dirty to the host when using a direct-assign device within a
    guest. The advantage to this approach is that it is fairly simple, however
    It currently has a singificant impact on device performance in all the
    scenerios where it won't be needed.

    As such this is really meant only as a proof of concept and to get the ball
    rolling in terms of figuring out how best to approach the issue of dirty
    page tracking for a guest that is using a direct assigned device. In
    addition with just this patch it should be possible to modify current
    migration approaches so that instead of having to hot-remove the device
    before starting the migration this can instead be delayed until the period
    before the final stop and copy.

    Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
    ---
    arch/arm/include/asm/dma-mapping.h | 3 ++-
    arch/arm64/include/asm/dma-mapping.h | 5 ++---
    arch/ia64/include/asm/dma.h | 1 +
    arch/mips/include/asm/dma-mapping.h | 1 +
    arch/powerpc/include/asm/swiotlb.h | 1 +
    arch/tile/include/asm/dma-mapping.h | 1 +
    arch/unicore32/include/asm/dma-mapping.h | 1 +
    arch/x86/Kconfig | 11 +++++++++++
    arch/x86/include/asm/swiotlb.h | 26 ++++++++++++++++++++++++++
    drivers/xen/swiotlb-xen.c | 6 ++++++
    lib/swiotlb.c | 6 ++++++
    11 files changed, 58 insertions(+), 4 deletions(-)

    diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
    index ccb3aa64640d..1962d7b471c7 100644
    --- a/arch/arm/include/asm/dma-mapping.h
    +++ b/arch/arm/include/asm/dma-mapping.h
    @@ -167,7 +167,8 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size)
    return 1;
    }

    -static inline void dma_mark_clean(void *addr, size_t size) { }
    +static inline void dma_mark_clean(void *addr, size_t size) {}
    +static inline void dma_mark_dirty(void *addr, size_t size) {}

    extern int arm_dma_set_mask(struct device *dev, u64 dma_mask);

    diff --git a/arch/arm64/include/asm/dma-mapping.h b/arch/arm64/include/asm/dma-mapping.h
    index 61e08f360e31..8d24fe11c8a3 100644
    --- a/arch/arm64/include/asm/dma-mapping.h
    +++ b/arch/arm64/include/asm/dma-mapping.h
    @@ -84,9 +84,8 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size)
    return addr + size - 1 <= *dev->dma_mask;
    }

    -static inline void dma_mark_clean(void *addr, size_t size)
    -{
    -}
    +static inline void dma_mark_clean(void *addr, size_t size) {}
    +static inline void dma_mark_dirty(void *addr, size_t size) {}

    #endif /* __KERNEL__ */
    #endif /* __ASM_DMA_MAPPING_H */
    diff --git a/arch/ia64/include/asm/dma.h b/arch/ia64/include/asm/dma.h
    index 4d97f60f1ef5..d92ebeb2758e 100644
    --- a/arch/ia64/include/asm/dma.h
    +++ b/arch/ia64/include/asm/dma.h
    @@ -20,5 +20,6 @@ extern unsigned long MAX_DMA_ADDRESS;
    #define free_dma(x)

    void dma_mark_clean(void *addr, size_t size);
    +static inline void dma_mark_dirty(void *addr, size_t size) {}

    #endif /* _ASM_IA64_DMA_H */
    diff --git a/arch/mips/include/asm/dma-mapping.h b/arch/mips/include/asm/dma-mapping.h
    index e604f760c4a0..567f6e03e337 100644
    --- a/arch/mips/include/asm/dma-mapping.h
    +++ b/arch/mips/include/asm/dma-mapping.h
    @@ -28,6 +28,7 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size)
    }

    static inline void dma_mark_clean(void *addr, size_t size) {}
    +static inline void dma_mark_dirty(void *addr, size_t size) {}

    #include <asm-generic/dma-mapping-common.h>

    diff --git a/arch/powerpc/include/asm/swiotlb.h b/arch/powerpc/include/asm/swiotlb.h
    index de99d6e29430..b694e8399e28 100644
    --- a/arch/powerpc/include/asm/swiotlb.h
    +++ b/arch/powerpc/include/asm/swiotlb.h
    @@ -16,6 +16,7 @@
    extern struct dma_map_ops swiotlb_dma_ops;

    static inline void dma_mark_clean(void *addr, size_t size) {}
    +static inline void dma_mark_dirty(void *addr, size_t size) {}

    extern unsigned int ppc_swiotlb_enable;
    int __init swiotlb_setup_bus_notifier(void);
    diff --git a/arch/tile/include/asm/dma-mapping.h b/arch/tile/include/asm/dma-mapping.h
    index 96ac6cce4a32..79953f09e938 100644
    --- a/arch/tile/include/asm/dma-mapping.h
    +++ b/arch/tile/include/asm/dma-mapping.h
    @@ -58,6 +58,7 @@ static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr)
    }

    static inline void dma_mark_clean(void *addr, size_t size) {}
    +static inline void dma_mark_dirty(void *addr, size_t size) {}

    static inline void set_dma_ops(struct device *dev, struct dma_map_ops *ops)
    {
    diff --git a/arch/unicore32/include/asm/dma-mapping.h b/arch/unicore32/include/asm/dma-mapping.h
    index 8140e053ccd3..b9d357ab122d 100644
    --- a/arch/unicore32/include/asm/dma-mapping.h
    +++ b/arch/unicore32/include/asm/dma-mapping.h
    @@ -49,6 +49,7 @@ static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr)
    }

    static inline void dma_mark_clean(void *addr, size_t size) {}
    +static inline void dma_mark_dirty(void *addr, size_t size) {}

    static inline void dma_cache_sync(struct device *dev, void *vaddr,
    size_t size, enum dma_data_direction direction)
    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index db3622f22b61..f0b09156d7d8 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -841,6 +841,17 @@ config SWIOTLB
    with more than 3 GB of memory.
    If unsure, say Y.

    +config SWIOTLB_PAGE_DIRTYING
    + bool "SWIOTLB page dirtying"
    + depends on SWIOTLB
    + default n
    + ---help---
    + SWIOTLB page dirtying support provides a means for the guest to
    + trigger write faults on pages which received DMA from the device
    + without changing the data contained within. By doing this the
    + guest can then support migration assuming the device and any
    + remaining pages are unmapped prior to the CPU itself being halted.
    +
    config IOMMU_HELPER
    def_bool y
    depends on CALGARY_IOMMU || GART_IOMMU || SWIOTLB || AMD_IOMMU
    diff --git a/arch/x86/include/asm/swiotlb.h b/arch/x86/include/asm/swiotlb.h
    index ab05d73e2bb7..7f9f2e76d081 100644
    --- a/arch/x86/include/asm/swiotlb.h
    +++ b/arch/x86/include/asm/swiotlb.h
    @@ -29,6 +29,32 @@ static inline void pci_swiotlb_late_init(void)

    static inline void dma_mark_clean(void *addr, size_t size) {}

    +/*
    + * Make certain that the pages get marked as dirty
    + * now that the device has completed the DMA transaction.
    + *
    + * Without this we run the risk of a guest migration missing
    + * the pages that the device has written to as they are not
    + * tracked as a part of the dirty page tracking.
    + */
    +static inline void dma_mark_dirty(void *addr, size_t size)
    +{
    +#ifdef CONFIG_SWIOTLB_PAGE_DIRTYING
    + unsigned long pg_addr, start;
    +
    + start = (unsigned long)addr;
    + pg_addr = PAGE_ALIGN(start + size);
    + start &= ~(sizeof(atomic_t) - 1);
    +
    + /* trigger a write fault on each page, excluding first page */
    + while ((pg_addr -= PAGE_SIZE) > start)
    + atomic_add(0, (atomic_t *)pg_addr);
    +
    + /* trigger a write fault on first word of DMA */
    + atomic_add(0, (atomic_t *)start);
    +#endif /* CONFIG_SWIOTLB_PAGE_DIRTYING */
    +}
    +
    extern void *x86_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
    dma_addr_t *dma_handle, gfp_t flags,
    struct dma_attrs *attrs);
    diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
    index 2154c70e47da..1533b3eefb67 100644
    --- a/drivers/xen/swiotlb-xen.c
    +++ b/drivers/xen/swiotlb-xen.c
    @@ -456,6 +456,9 @@ void xen_swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
    */
    if (dir == DMA_FROM_DEVICE)
    dma_mark_clean(phys_to_virt(paddr), size);
    +
    + if (dir != DMA_TO_DEVICE)
    + dma_mark_dirty(phys_to_virt(paddr), size);
    }
    EXPORT_SYMBOL_GPL(xen_swiotlb_unmap_page);

    @@ -485,6 +488,9 @@ xen_swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,

    if (dir == DMA_FROM_DEVICE)
    dma_mark_clean(phys_to_virt(paddr), size);
    +
    + if (dir != DMA_TO_DEVICE)
    + dma_mark_dirty(phys_to_virt(paddr), size);
    }
    EXPORT_SYMBOL_GPL(xen_swiotlb_sync_single_for_cpu);

    diff --git a/lib/swiotlb.c b/lib/swiotlb.c
    index 384ac06217b2..4223d6c54724 100644
    --- a/lib/swiotlb.c
    +++ b/lib/swiotlb.c
    @@ -802,6 +802,9 @@ void swiotlb_unmap_page(struct device *hwdev, dma_addr_t dev_addr,
    */
    if (dir == DMA_FROM_DEVICE)
    dma_mark_clean(phys_to_virt(paddr), size);
    +
    + if (dir != DMA_TO_DEVICE)
    + dma_mark_dirty(phys_to_virt(paddr), size);
    }
    EXPORT_SYMBOL_GPL(swiotlb_unmap_page);

    @@ -830,6 +833,9 @@ swiotlb_sync_single_for_cpu(struct device *hwdev, dma_addr_t dev_addr,

    if (dir == DMA_FROM_DEVICE)
    dma_mark_clean(phys_to_virt(paddr), size);
    +
    + if (dir != DMA_TO_DEVICE)
    + dma_mark_dirty(phys_to_virt(paddr), size);
    }
    EXPORT_SYMBOL(swiotlb_sync_single_for_cpu);



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