[Xen-devel] [PATCH V1] xen/arm: domain_build: introduce dom0_lowmem bootargs

[Peng Fan <van.freenix@xxxxxxxxx>]

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@xxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
---

RFC->V1:
 This patch is to resolve the issue in 
https://lists.xen.org/archives/html/xen-devel/2016-09/msg00235.html
 No code change since RFC.
 Tested on xen-4.8 unstable with AArch64. See partial log:
 "dom0_mem = 2048M  dom0_lowmem=128M"
 (XEN) Allocated 0x00000088000000-0x00000090000000 (128MB/2048MB, order 15)
 (XEN) Allocated 0x00000880000000-0x000008c0000000 (1024MB/1920MB, order 18)
 (XEN) Allocated 0x000009c0000000-0x000009e0000000 (512MB/896MB, order 17)
 (XEN) Allocated 0x000009e0000000-0x000009f0000000 (256MB/384MB, order 16)
 (XEN) Allocated 0x000008f8000000-0x00000900000000 (128MB/128MB, order 15)

 "dom0_mem = 2048M  dom0_lowmem=1024M"
 (XEN) Allocated 0x000000a0000000-0x000000c0000000 (512MB/2048MB, order 17)
 (XEN) Allocated 0x000000c0000000-0x000000e0000000 (512MB/1536MB, order 17)
 (XEN) Allocated 0x00000880000000-0x000008c0000000 (1024MB/1024MB, order 18)

 "dom0_mem = 1024M  dom0_lowmem=1024M"
 (XEN) Allocated 0x000000a0000000-0x000000c0000000 (512MB/1024MB, order 17)
 (XEN) Allocated 0x000000c0000000-0x000000e0000000 (512MB/512MB, order 17)

 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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