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SubjectRe: [PATCH v6 06/19] xen/arm,arm64: enable SWIOTLB_XEN
On Fri, Sep 27, 2013 at 05:09:54PM +0100, Stefano Stabellini wrote:
> Xen on arm and arm64 needs SWIOTLB_XEN: when running on Xen we need to
> program the hardware with mfns rather than pfns for dma addresses.
> Remove SWIOTLB_XEN dependency on X86 and PCI and make XEN select
> SWIOTLB_XEN on arm and arm64.
>
> At the moment always rely on swiotlb-xen, but when Xen starts supporting
> hardware IOMMUs we'll be able to avoid it conditionally on the presence
> of an IOMMU on the platform.
>
> Implement xen_create_contiguous_region on arm and arm64 by using
> XENMEM_exchange_and_pin.
>
> Initialize the xen-swiotlb from xen_early_init (before the native
> dma_ops are initialized), set xen_dma_ops to &xen_swiotlb_dma_ops.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>
>
> Changes in v6:
> - introduce and export xen_dma_ops;
> - call xen_mm_init from as arch_initcall.
>
> Changes in v4:
> - remove redefinition of DMA_ERROR_CODE;
> - update the code to use XENMEM_exchange_and_pin and XENMEM_unpin;
> - add a note about hardware IOMMU in the commit message.
>
> Changes in v3:
> - code style changes;
> - warn on XENMEM_put_dma_buf failures.
> ---
> arch/arm/Kconfig | 1 +
> arch/arm/include/asm/xen/hypervisor.h | 2 +
> arch/arm/include/asm/xen/page.h | 2 +
> arch/arm/xen/Makefile | 2 +-
> arch/arm/xen/mm.c | 121 +++++++++++++++++++++++++++++++++
> arch/arm64/Kconfig | 1 +
> arch/arm64/xen/Makefile | 2 +-
> drivers/xen/Kconfig | 1 -
> drivers/xen/swiotlb-xen.c | 16 +++++
> 9 files changed, 145 insertions(+), 3 deletions(-)
> create mode 100644 arch/arm/xen/mm.c
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index c0bfb33..2c9d112 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1848,6 +1848,7 @@ config XEN
> depends on CPU_V7 && !CPU_V6
> depends on !GENERIC_ATOMIC64
> select ARM_PSCI
> + select SWIOTLB_XEN
> help
> Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.
>
> diff --git a/arch/arm/include/asm/xen/hypervisor.h b/arch/arm/include/asm/xen/hypervisor.h
> index d7ab99a..1317ee4 100644
> --- a/arch/arm/include/asm/xen/hypervisor.h
> +++ b/arch/arm/include/asm/xen/hypervisor.h
> @@ -16,4 +16,6 @@ static inline enum paravirt_lazy_mode paravirt_get_lazy_mode(void)
> return PARAVIRT_LAZY_NONE;
> }
>
> +extern struct dma_map_ops *xen_dma_ops;
> +
> #endif /* _ASM_ARM_XEN_HYPERVISOR_H */
> diff --git a/arch/arm/include/asm/xen/page.h b/arch/arm/include/asm/xen/page.h
> index 359a7b5..b0f7150 100644
> --- a/arch/arm/include/asm/xen/page.h
> +++ b/arch/arm/include/asm/xen/page.h
> @@ -6,12 +6,14 @@
>
> #include <linux/pfn.h>
> #include <linux/types.h>
> +#include <linux/dma-mapping.h>
>
> #include <xen/interface/grant_table.h>
>
> #define pfn_to_mfn(pfn) (pfn)
> #define phys_to_machine_mapping_valid(pfn) (1)
> #define mfn_to_pfn(mfn) (mfn)
> +#define mfn_to_local_pfn(m) (mfn_to_pfn(m))
> #define mfn_to_virt(m) (__va(mfn_to_pfn(m) << PAGE_SHIFT))
>
> #define pte_mfn pte_pfn
> diff --git a/arch/arm/xen/Makefile b/arch/arm/xen/Makefile
> index 4384103..66fc35d 100644
> --- a/arch/arm/xen/Makefile
> +++ b/arch/arm/xen/Makefile
> @@ -1 +1 @@
> -obj-y := enlighten.o hypercall.o grant-table.o
> +obj-y := enlighten.o hypercall.o grant-table.o mm.o
> diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> new file mode 100644
> index 0000000..b065c98
> --- /dev/null
> +++ b/arch/arm/xen/mm.c
> @@ -0,0 +1,121 @@
> +#include <linux/bootmem.h>
> +#include <linux/gfp.h>
> +#include <linux/export.h>
> +#include <linux/slab.h>
> +#include <linux/types.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/vmalloc.h>
> +#include <linux/swiotlb.h>
> +
> +#include <xen/xen.h>
> +#include <xen/interface/memory.h>
> +#include <xen/swiotlb-xen.h>
> +
> +#include <asm/cacheflush.h>
> +#include <asm/xen/page.h>
> +#include <asm/xen/hypercall.h>
> +#include <asm/xen/interface.h>
> +
> +static int xen_exchange_memory(xen_ulong_t extents_in,
> + unsigned int order_in,
> + xen_pfn_t *pfns_in,
> + xen_ulong_t extents_out,
> + unsigned int order_out,
> + xen_pfn_t *mfns_out,
> + unsigned int address_bits)
> +{
> + long rc;
> + int success;
> +
> + struct xen_memory_exchange exchange = {
> + .in = {
> + .nr_extents = extents_in,
> + .extent_order = order_in,
> + .domid = DOMID_SELF
> + },
> + .out = {
> + .nr_extents = extents_out,
> + .extent_order = order_out,
> + .address_bits = address_bits,
> + .domid = DOMID_SELF
> + }

I think you need to set .nr_exchange = 0 just in case there is
garbage on the stack and the hypercall is -ENOSYS.

> + };
> + set_xen_guest_handle(exchange.in.extent_start, pfns_in);
> + set_xen_guest_handle(exchange.out.extent_start, mfns_out);
> +
> + BUG_ON(extents_in << order_in != extents_out << order_out);
> +
> +
> + rc = HYPERVISOR_memory_op(XENMEM_exchange_and_pin, &exchange);
> + success = (exchange.nr_exchanged == extents_in);
> +
> + BUG_ON(!success && ((exchange.nr_exchanged != 0) || (rc == 0)));

I think you need to set nr_exchange = 0 before you make the hypercall.
Ohterwise you can get this:

a). Say rc = -ENOSYS, in which case the exchage.nr_exchange won't be touched.
success = 0

BUG(!0 && (<garbage> != 0)) <= BOOM.

If the hypercall failed (say -EBUSY), so we have:
success = 0

BUG(!0 && (1)) <= BOOM

Which I thought would be more of a normal error - and we would
just return the number of succesfull operations.

> + BUG_ON(success && (rc != 0));
> +
> + return success;
> +}
> +
> +int xen_create_contiguous_region(unsigned long vstart, unsigned int order,
> + unsigned int address_bits,
> + dma_addr_t *dma_handle)
> +{
> + phys_addr_t pstart = __pa(vstart);
> + xen_pfn_t in_frame, out_frame;
> + int success;
> +
> + /* Get a new contiguous memory extent. */
> + in_frame = out_frame = pstart >> PAGE_SHIFT;
> + success = xen_exchange_memory(1, order, &in_frame,
> + 1, order, &out_frame,
> + address_bits);
> +
> + if (!success)
> + return -ENOMEM;
> +
> + *dma_handle = out_frame << PAGE_SHIFT;
> +
> + return success ? 0 : -ENOMEM;
> +}
> +EXPORT_SYMBOL_GPL(xen_create_contiguous_region);
> +
> +void xen_destroy_contiguous_region(unsigned long vstart, unsigned int order)
> +{
> + xen_pfn_t in_frame = __pa(vstart) >> PAGE_SHIFT;
> + struct xen_unpin unpin = {
> + .in = {
> + .nr_extents = 1,
> + .extent_order = order,
> + .domid = DOMID_SELF
> + },
> + };
> + set_xen_guest_handle(unpin.in.extent_start, &in_frame);
> +
> + WARN_ON(HYPERVISOR_memory_op(XENMEM_unpin, &unpin));
> +}
> +EXPORT_SYMBOL_GPL(xen_destroy_contiguous_region);
> +
> +struct dma_map_ops *xen_dma_ops;
> +EXPORT_SYMBOL_GPL(xen_dma_ops);
> +
> +static struct dma_map_ops xen_swiotlb_dma_ops = {
> + .mapping_error = xen_swiotlb_dma_mapping_error,
> + .alloc = xen_swiotlb_alloc_coherent,
> + .free = xen_swiotlb_free_coherent,
> + .sync_single_for_cpu = xen_swiotlb_sync_single_for_cpu,
> + .sync_single_for_device = xen_swiotlb_sync_single_for_device,
> + .sync_sg_for_cpu = xen_swiotlb_sync_sg_for_cpu,
> + .sync_sg_for_device = xen_swiotlb_sync_sg_for_device,
> + .map_sg = xen_swiotlb_map_sg_attrs,
> + .unmap_sg = xen_swiotlb_unmap_sg_attrs,
> + .map_page = xen_swiotlb_map_page,
> + .unmap_page = xen_swiotlb_unmap_page,
> + .dma_supported = xen_swiotlb_dma_supported,
> +};
> +
> +int __init xen_mm_init(void)
> +{
> + xen_swiotlb_init(1, false);
> + xen_dma_ops = &xen_swiotlb_dma_ops;
> + return 0;
> +}
> +arch_initcall(xen_mm_init);
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 9737e97..aa1f6fb 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -209,6 +209,7 @@ config XEN_DOM0
> config XEN
> bool "Xen guest support on ARM64 (EXPERIMENTAL)"
> depends on ARM64 && OF
> + select SWIOTLB_XEN
> help
> Say Y if you want to run Linux in a Virtual Machine on Xen on ARM64.
>
> diff --git a/arch/arm64/xen/Makefile b/arch/arm64/xen/Makefile
> index be24040..0ef9637 100644
> --- a/arch/arm64/xen/Makefile
> +++ b/arch/arm64/xen/Makefile
> @@ -1,2 +1,2 @@
> -xen-arm-y += $(addprefix ../../arm/xen/, enlighten.o grant-table.o)
> +xen-arm-y += $(addprefix ../../arm/xen/, enlighten.o grant-table.o mm.o)
> obj-y := xen-arm.o hypercall.o
> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
> index 9e02d60..7e83688 100644
> --- a/drivers/xen/Kconfig
> +++ b/drivers/xen/Kconfig
> @@ -140,7 +140,6 @@ config XEN_GRANT_DEV_ALLOC
>
> config SWIOTLB_XEN
> def_bool y
> - depends on PCI && X86
> select SWIOTLB
>
> config XEN_TMEM
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 84aef43..a1cb0f4 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -45,6 +45,8 @@
> #include <xen/xen-ops.h>
> #include <xen/hvc-console.h>
> #include <xen/features.h>
> +#include <asm/dma-mapping.h>
> +
> /*
> * Used to do a quick range check in swiotlb_tbl_unmap_single and
> * swiotlb_tbl_sync_single_*, to see if the memory was in fact allocated by this
> @@ -58,6 +60,20 @@ static unsigned long xen_io_tlb_nslabs;
> * Quick lookup value of the bus address of the IOTLB.
> */
>
> +#ifndef CONFIG_X86
> +static unsigned long dma_alloc_coherent_mask(struct device *dev,
> + gfp_t gfp)
> +{
> + unsigned long dma_mask = 0;
> +
> + dma_mask = dev->coherent_dma_mask;
> + if (!dma_mask)
> + dma_mask = (gfp & GFP_DMA) ? DMA_BIT_MASK(24) : DMA_BIT_MASK(32);
> +
> + return dma_mask;
> +}
> +#endif
> +
> struct xen_dma_info {
> dma_addr_t dma_addr;
> phys_addr_t phys_addr;
> --
> 1.7.2.5
>


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