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Re: [Xen-devel] [PATCH for-4.9] xen/arm: acpi: Map MMIO on fault in stage-2 page table for the hardware domain



Hi Stefano,

On 30/03/17 19:37, Stefano Stabellini wrote:
On Thu, 30 Mar 2017, Julien Grall wrote:
+/*
+ * When using ACPI, most of the MMIO regions will be mapped on-demand
+ * in stage-2 page tables for the hardware domain because Xen is not
+ * able to know from the EFI memory map the MMIO regions.
+ */
+static bool try_map_mmio(gfn_t gfn)
+{
+    struct domain *d = current->domain;
+
+    /* For the hardware domain, all MMIOs are mapped with GFN == MFN */
+    mfn_t mfn = _mfn(gfn_x(gfn));
+
+    /*
+     * Device-Tree should already have everything mapped when building
+     * the hardware domain.
+     */
+    if ( acpi_disabled )
+        return false;
+
+    if ( d != hardware_domain )

is_hardware_domain(d)

Will fix it.


+        return false;
+
+    /* The hardware domain can only map permitted MMIO regions */
+    if ( !iomem_access_permitted(d, mfn_x(mfn), mfn_x(mfn) + 1) )
+        return false;

Because of the potential of causing problems with DMA to device MMIO,
I would add a warning here, something like:

   dprintk(XENLOG_WARNING, "Mapping gfn=mfn=%"PRI_gfn" to Dom%d\n", 
d->domain_id);

I hope that it will help us debug issues when/if we'll actually
encounter such a case.

I don't think this will help us and it will flood the console in debug-build (there are a lot of MMIO to map).

When SMMUs are not used, DMA to device MMIO will work regardless the mapping in stage-2.

When SMMUs are in use, you will get a SMMU fault that tells you the address used. With that you could know the region was not mapped.

Cheers,

--
Julien Grall

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