Re: [PATCH] xen/arm: introduce XENFEAT_direct_mapped and XENFEAT_not_direct_mapped

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Gentle ping, now that the Xen side is acked (not committed due to the
imminent release):

https://marc.info/?l=xen-devel&m=161559099506456


On Thu, 25 Feb 2021, Stefano Stabellini wrote:

> Newer Xen versions expose two Xen feature flags to tell us if the domain
> is directly mapped or not. Only when a domain is directly mapped it
> makes sense to enable swiotlb-xen on ARM.
> 
> Introduce a function on ARM to check the new Xen feature flags and also
> to deal with the legacy case. Call the function xen_swiotlb_detect.
> 
> Also rename the existing pci_xen_swiotlb_detect on x86 to
> xen_swiotlb_detect so that we can share a common function declaration.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> ---
> 
> This is the corresponding Xen patch under review:
> https://marc.info/?l=xen-devel&m=161421618217686
> 
> We don't *have to* make the x86 function and the ARM function exactly
> the same, but I thought it would be much nicer if we did. However, we
> can't really call it pci_* on ARM as there is no PCI necessarily.
> 
> ---
>  arch/arm/xen/mm.c                      | 14 +++++++++++++-
>  arch/arm64/mm/dma-mapping.c            |  2 +-
>  arch/x86/include/asm/xen/swiotlb-xen.h |  4 ++--
>  arch/x86/kernel/pci-swiotlb.c          |  2 +-
>  arch/x86/xen/pci-swiotlb-xen.c         |  6 +++---
>  include/xen/interface/features.h       |  7 +++++++
>  include/xen/swiotlb-xen.h              |  6 ++++++
>  7 files changed, 33 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/xen/mm.c b/arch/arm/xen/mm.c
> index 467fa225c3d0..f8e5acbef05d 100644
> --- a/arch/arm/xen/mm.c
> +++ b/arch/arm/xen/mm.c
> @@ -135,10 +135,22 @@ void xen_destroy_contiguous_region(phys_addr_t pstart, 
> unsigned int order)
>       return;
>  }
>  
> +int __init xen_swiotlb_detect(void)
> +{
> +     if (!xen_domain())
> +             return 0;
> +     if (xen_feature(XENFEAT_direct_mapped))
> +             return 1;
> +     /* legacy case */
> +     if (!xen_feature(XENFEAT_not_direct_mapped) && xen_initial_domain())
> +             return 1;
> +     return 0;
> +}
> +
>  static int __init xen_mm_init(void)
>  {
>       struct gnttab_cache_flush cflush;
> -     if (!xen_initial_domain())
> +     if (!xen_swiotlb_detect())
>               return 0;
>       xen_swiotlb_init(1, false);
>  
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index 93e87b287556..4bf1dd3eb041 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -53,7 +53,7 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, 
> u64 size,
>               iommu_setup_dma_ops(dev, dma_base, size);
>  
>  #ifdef CONFIG_XEN
> -     if (xen_initial_domain())
> +     if (xen_swiotlb_detect())
>               dev->dma_ops = &xen_swiotlb_dma_ops;
>  #endif
>  }
> diff --git a/arch/x86/include/asm/xen/swiotlb-xen.h 
> b/arch/x86/include/asm/xen/swiotlb-xen.h
> index 6b56d0d45d15..494694744844 100644
> --- a/arch/x86/include/asm/xen/swiotlb-xen.h
> +++ b/arch/x86/include/asm/xen/swiotlb-xen.h
> @@ -2,14 +2,14 @@
>  #ifndef _ASM_X86_SWIOTLB_XEN_H
>  #define _ASM_X86_SWIOTLB_XEN_H
>  
> +#include <xen/swiotlb-xen.h>
> +
>  #ifdef CONFIG_SWIOTLB_XEN
>  extern int xen_swiotlb;
> -extern int __init pci_xen_swiotlb_detect(void);
>  extern void __init pci_xen_swiotlb_init(void);
>  extern int pci_xen_swiotlb_init_late(void);
>  #else
>  #define xen_swiotlb (0)
> -static inline int __init pci_xen_swiotlb_detect(void) { return 0; }
>  static inline void __init pci_xen_swiotlb_init(void) { }
>  static inline int pci_xen_swiotlb_init_late(void) { return -ENXIO; }
>  #endif
> diff --git a/arch/x86/kernel/pci-swiotlb.c b/arch/x86/kernel/pci-swiotlb.c
> index c2cfa5e7c152..c18eb6629326 100644
> --- a/arch/x86/kernel/pci-swiotlb.c
> +++ b/arch/x86/kernel/pci-swiotlb.c
> @@ -30,7 +30,7 @@ int __init pci_swiotlb_detect_override(void)
>       return swiotlb;
>  }
>  IOMMU_INIT_FINISH(pci_swiotlb_detect_override,
> -               pci_xen_swiotlb_detect,
> +               xen_swiotlb_detect,
>                 pci_swiotlb_init,
>                 pci_swiotlb_late_init);
>  
> diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c
> index 19ae3e4fe4e9..0a35657eeb85 100644
> --- a/arch/x86/xen/pci-swiotlb-xen.c
> +++ b/arch/x86/xen/pci-swiotlb-xen.c
> @@ -21,12 +21,12 @@
>  int xen_swiotlb __read_mostly;
>  
>  /*
> - * pci_xen_swiotlb_detect - set xen_swiotlb to 1 if necessary
> + * xen_swiotlb_detect - set xen_swiotlb to 1 if necessary
>   *
>   * This returns non-zero if we are forced to use xen_swiotlb (by the boot
>   * option).
>   */
> -int __init pci_xen_swiotlb_detect(void)
> +int __init xen_swiotlb_detect(void)
>  {
>  
>       if (!xen_pv_domain())
> @@ -90,7 +90,7 @@ int pci_xen_swiotlb_init_late(void)
>  }
>  EXPORT_SYMBOL_GPL(pci_xen_swiotlb_init_late);
>  
> -IOMMU_INIT_FINISH(pci_xen_swiotlb_detect,
> +IOMMU_INIT_FINISH(xen_swiotlb_detect,
>                 NULL,
>                 pci_xen_swiotlb_init,
>                 NULL);
> diff --git a/include/xen/interface/features.h 
> b/include/xen/interface/features.h
> index 6d1384abfbdf..f0d00bb0ac63 100644
> --- a/include/xen/interface/features.h
> +++ b/include/xen/interface/features.h
> @@ -83,6 +83,13 @@
>   */
>  #define XENFEAT_linux_rsdp_unrestricted   15
>  
> +/*
> + * A direct-mapped (or 1:1 mapped) domain is a domain for which its
> + * local pages have gfn == mfn.
> + */
> +#define XENFEAT_not_direct_mapped         16
> +#define XENFEAT_direct_mapped             17
> +
>  #define XENFEAT_NR_SUBMAPS 1
>  
>  #endif /* __XEN_PUBLIC_FEATURES_H__ */
> diff --git a/include/xen/swiotlb-xen.h b/include/xen/swiotlb-xen.h
> index d5eaf9d682b8..6a2fc4e4b838 100644
> --- a/include/xen/swiotlb-xen.h
> +++ b/include/xen/swiotlb-xen.h
> @@ -12,4 +12,10 @@ void xen_dma_sync_for_device(struct device *dev, 
> dma_addr_t handle,
>  extern int xen_swiotlb_init(int verbose, bool early);
>  extern const struct dma_map_ops xen_swiotlb_dma_ops;
>  
> +#ifdef CONFIG_SWIOTLB_XEN
> +extern int __init xen_swiotlb_detect(void);
> +#else
> +static inline int __init xen_swiotlb_detect(void) { return 0; }
> +#endif
> +
>  #endif /* __LINUX_SWIOTLB_XEN_H */
> -- 
> 2.17.1
>