[PATCH] xen/arm: introduce XENFEAT_direct_mapped and XENFEAT_not_direct_mapped

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

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