[xen staging] xen/arm: fix gnttab_need_iommu_mapping

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commit 04085ec1ac05a362812e9b0c6b5a8713d7dc88ad
Author:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
AuthorDate: Mon Feb 8 10:49:32 2021 -0800
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Fri Feb 12 11:01:41 2021 -0800

    xen/arm: fix gnttab_need_iommu_mapping
    
    Commit 91d4eca7add broke gnttab_need_iommu_mapping on ARM.
    The offending chunk is:
    
     #define gnttab_need_iommu_mapping(d)                    \
    -    (is_domain_direct_mapped(d) && need_iommu(d))
    +    (is_domain_direct_mapped(d) && need_iommu_pt_sync(d))
    
    On ARM we need gnttab_need_iommu_mapping to be true for dom0 when it is
    directly mapped and IOMMU is enabled for the domain, like the old check
    did, but the new check is always false.
    
    In fact, need_iommu_pt_sync is defined as dom_iommu(d)->need_sync and
    need_sync is set as:
    
        if ( !is_hardware_domain(d) || iommu_hwdom_strict )
            hd->need_sync = !iommu_use_hap_pt(d);
    
    iommu_use_hap_pt(d) means that the page-table used by the IOMMU is the
    P2M. It is true on ARM. need_sync means that you have a separate IOMMU
    page-table and it needs to be updated for every change. need_sync is set
    to false on ARM. Hence, gnttab_need_iommu_mapping(d) is false too,
    which is wrong.
    
    As a consequence, when using PV network from a domU on a system where
    IOMMU is on from Dom0, I get:
    
    (XEN) smmu: /smmu@fd800000: Unhandled context fault: fsr=0x402, 
iova=0x8424cb148, fsynr=0xb0001, cb=0
    [   68.290307] macb ff0e0000.ethernet eth0: DMA bus error: HRESP not OK
    
    The fix is to go back to something along the lines of the old
    implementation of gnttab_need_iommu_mapping.
    
    Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
    Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
    Fixes: 91d4eca7add ("mm / iommu: split need_iommu() into has_iommu_pt() and 
need_iommu_pt_sync()")
    Backport: 4.13+
---
 xen/include/asm-arm/grant_table.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/include/asm-arm/grant_table.h 
b/xen/include/asm-arm/grant_table.h
index 6f585b1538..0ce77f9a1c 100644
--- a/xen/include/asm-arm/grant_table.h
+++ b/xen/include/asm-arm/grant_table.h
@@ -89,7 +89,7 @@ int replace_grant_host_mapping(unsigned long gpaddr, mfn_t 
mfn,
     (((i) >= nr_status_frames(t)) ? INVALID_GFN : (t)->arch.status_gfn[i])
 
 #define gnttab_need_iommu_mapping(d)                    \
-    (is_domain_direct_mapped(d) && need_iommu_pt_sync(d))
+    (is_domain_direct_mapped(d) && is_iommu_enabled(d))
 
 #endif /* __ASM_GRANT_TABLE_H__ */
 /*
--
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