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

[Peng Fan <van.freenix@xxxxxxxxx>]

Hello Julien,
On Wed, Sep 14, 2016 at 08:23:24AM +0100, Julien Grall wrote:
>Hello,
>
>On 14/09/2016 06:12, Peng Fan wrote:
>>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.
>
>See my comments on v1, I still don't think this new parameter is useful.

Thanks for comments. I see :)

>
>The commit message does not explain what is the advantage to only allocate a
>bit of low mem and not as much as we can (as we do on for 32-bit dom0).

This patch is just want to resolve the issue in
https://lists.xen.org/archives/html/xen-devel/2016-09/msg00235.html.
I am not keen on the method in this patch, a bit complicated.
The method in this patch is try to allocate the size lowmem indicated in 
bootargs.

Rethinking about DomU, seems allocate as much as possible lowmem for Dom0 is ok.

Then, do you agree to use the following patch?
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 35ab08d..cc71e6f 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -28,6 +28,8 @@
 
static unsigned int __initdata opt_dom0_max_vcpus;
integer_param("dom0_max_vcpus", opt_dom0_max_vcpus);
+static bool_t __initdata opt_dom0_use_lowmem;
+boolean_param("dom0_use_lowmem", opt_dom0_use_lowmem);
    
int dom0_11_mapping = 1;
      
@@ -244,7 +246,7 @@ 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) || opt_dom0_use_lowmem;
     unsigned int bits;


Pass "dom0_use_lowmem=1" to xen to allocate lowmem as much as possible.

>
>>
>>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)
>
>The comment on top of allocate_memory should be updated.
>
>>     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;
>
>Why do you spread the lowmem = is_32_bit_domain(d) || !!dom0_lowmem
>everywhere?

If the first allocation does not allocate the needed lowmem, the following 
allocation
will continue allocate 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);
>>+
>
>BUG_ON should not be used to check user input validity.

Thanks, get it.

Regards,
Peng.

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