[RFC] xen/arm: domain_build: introduce dom0_lowmem bootargs

[Peng Fan <van.freenix@gmail.com>]

On AArch64 SoCs, some IPs may only have the capability to access
32bits address space. The physical memory assigned for Dom0 maybe
not in 4GB address space, then the IPs will not work properly.

Introduce dom0_lowmem bootargs, user could pass "dom0_lowmem=xx"
to xen. It means how much memory user would like to be allocated
in lower 4GB memory space. If there is not enough memory for
dom0_lowmem, higher memory will be allocated.

Thinking such a memory layout on an AArch64 SoC:
Region 0: 2GB(0x80000000 - 0xffffffff)
Region 1: 4GB(0x880000000 - 0x97fffffff)
If user would like to assign 2GB for Dom0 and 1GB of the 2GB memory
in Region 0, user could pass "dom0=2048M dom0_lowmem=1024M" to xen.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Julien Grall <julien.grall@arm.com>
---

This patch is to resolve the issue mentioned in
https://lists.xen.org/archives/html/xen-devel/2016-09/msg00235.html
This patch not tested on latest 4.8-unstable, I only tested similar
patch on xen 4.7 on AArch64 platform.

The idea of patch is that user could specify the lowmem that user would
like to use. I rethought the ideas in https://lists.xen.org/archives/html/xen-devel/2016-09/msg00487.html,
but that is not good. lowmem is precise, it maybe used for some IPs that maybe
passthrough to DomU, so we only allocate the needed memory for Dom0.

 xen/arch/arm/domain_build.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 35ab08d..0f53bba 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -33,6 +33,8 @@ int dom0_11_mapping = 1;
 
 #define DOM0_MEM_DEFAULT 0x8000000 /* 128 MiB */
 static u64 __initdata dom0_mem = DOM0_MEM_DEFAULT;
+/* Only for AArch64 */
+static u64 __initdata dom0_lowmem;
 
 static void __init parse_dom0_mem(const char *s)
 {
@@ -42,6 +44,12 @@ static void __init parse_dom0_mem(const char *s)
 }
 custom_param("dom0_mem", parse_dom0_mem);
 
+static void __init parse_dom0_lowmem(const char *s)
+{
+    dom0_lowmem = parse_size_and_unit(s, &s);
+}
+custom_param("dom0_lowmem", parse_dom0_lowmem);
+
 //#define DEBUG_11_ALLOCATION
 #ifdef DEBUG_11_ALLOCATION
 # define D11PRINT(fmt, args...) printk(XENLOG_DEBUG fmt, ##args)
@@ -244,7 +252,7 @@ static void allocate_memory(struct domain *d, struct kernel_info *kinfo)
     unsigned int order = get_11_allocation_size(kinfo->unassigned_mem);
     int i;
 
-    bool_t lowmem = is_32bit_domain(d);
+    bool_t lowmem = is_32bit_domain(d) || !!dom0_lowmem;
     unsigned int bits;
 
     /*
@@ -263,6 +271,9 @@ static void allocate_memory(struct domain *d, struct kernel_info *kinfo)
      * First try and allocate the largest thing we can as low as
      * possible to be bank 0.
      */
+    if ( dom0_lowmem )
+        order = get_order_from_bytes(dom0_lowmem);
+
     while ( order >= min_low_order )
     {
         for ( bits = order ; bits <= (lowmem ? 32 : PADDR_BITS); bits++ )
@@ -278,6 +289,11 @@ static void allocate_memory(struct domain *d, struct kernel_info *kinfo)
 
  got_bank0:
 
+    if ( dom0_lowmem ) {
+        dom0_lowmem -= pfn_to_paddr((1 << order));
+        lowmem = is_32bit_domain(d) || !!dom0_lowmem;
+    }
+
     if ( !insert_11_bank(d, kinfo, pg, order) )
         BUG(); /* Cannot fail for first bank */
 
@@ -325,6 +341,16 @@ static void allocate_memory(struct domain *d, struct kernel_info *kinfo)
             }
         }
 
+        if ( dom0_lowmem && lowmem )
+        {
+            dom0_lowmem -= pfn_to_paddr((1 << order));
+            lowmem = is_32bit_domain(d) || !!dom0_lowmem;
+        }
+	else
+        {
+            lowmem = false;
+        }
+
         /*
          * Success, next time around try again to get the largest order
          * allocation possible.
@@ -2098,6 +2124,8 @@ int construct_dom0(struct domain *d)
 
     d->max_pages = ~0U;
 
+    BUG_ON(dom0_mem < dom0_lowmem);
+
     kinfo.unassigned_mem = dom0_mem;
 
     rc = kernel_probe(&kinfo);
-- 
2.6.6


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