[Xen-devel] [PATCH 3/8] xen/setup: Set identity mapping for non-RAM E820 and E820 gaps.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

We walk the E820 region and start at 0 (for PV guests we start
at ISA_END_ADDRESS) and skip any E820 RAM regions. For all other
regions and as well the gaps we set them to be identity mappings.

The reasons we do not want to set the identity mapping from 0->
ISA_END_ADDRESS when running as PV is b/c that the kernel would
try to read DMI information and fail (no permissions to read that).

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/setup.c |   39 +++++++++++++++++++++++++++++++++++++++
 1 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 7201800..643b3fc 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -143,6 +143,38 @@ static unsigned long __init 
xen_return_unused_memory(unsigned long max_pfn,
        return released;
 }
 
+static unsigned long __init xen_set_identity(const struct e820map *e820)
+{
+       phys_addr_t last = xen_initial_domain() ? 0 : ISA_END_ADDRESS;
+       int i;
+       unsigned long identity = 0;
+       unsigned long pfn;
+
+       for (i = 0; i < e820->nr_map; i++) {
+               phys_addr_t start = e820->map[i].addr;
+               phys_addr_t end = start + e820->map[i].size;
+
+               if (end < start)
+                       continue;
+
+               /* Skip over the 1MB region. */
+               if (last > end)
+                       continue;
+
+               if (e820->map[i].type == E820_RAM) {
+                       /* Without saving 'last' we would gooble RAM too. */
+                       last = end;
+                       continue;
+               }
+
+               for (pfn = PFN_UP(last); pfn < PFN_DOWN(end); pfn++)
+                       __set_phys_to_machine(pfn, pfn);
+               identity += pfn - PFN_UP(last);
+
+               last = end;
+       }
+       return identity;
+}
 /**
  * machine_specific_memory_setup - Hook for machine specific memory setup.
  **/
@@ -156,6 +188,7 @@ char * __init xen_memory_setup(void)
        struct xen_memory_map memmap;
        unsigned long extra_pages = 0;
        unsigned long extra_limit;
+       unsigned long identity_pages = 0;
        int i;
        int op;
 
@@ -251,6 +284,12 @@ char * __init xen_memory_setup(void)
 
        xen_add_extra_mem(extra_pages);
 
+       /*
+        * Set P2M for all non-RAM pages and E820 gaps to be identity
+        * type PFNs.
+        */
+       identity_pages = xen_set_identity(&e820);
+       printk(KERN_INFO "Set %ld page(s) to 1-1 mapping.\n", identity_pages);
        return "Xen";
 }
 
-- 
1.7.1


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