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Re: [PATCH 8/9] xen/arm: check `xen,static-mem` property during domain construction

On 06/07/2021 07:31, Penny Zheng wrote:


-----Original Message-----
From: Julien Grall <julien@xxxxxxx>
Sent: Saturday, July 3, 2021 9:26 PM
To: Penny Zheng <Penny.Zheng@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx;
sstabellini@xxxxxxxxxx; jbeulich@xxxxxxxx
Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>; Wei Chen
Subject: Re: [PATCH 8/9] xen/arm: check `xen,static-mem` property during
domain construction

Hi Penny,

On 07/06/2021 03:43, Penny Zheng wrote:
This commit checks `xen,static-mem` device tree property in /domUx
node, to determine whether domain is on Static Allocation, when
constructing domain during boot-up.

Right now, the implementation of allocate_static_memory is missing,
and will be introduced later. It just BUG() out at the moment.

And if the `memory` property and `xen,static-mem` are both set, it
shall be verified that if the memory size defined in both is consistent.

Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
changes v2:
- remove parsing procedure here
- check the consistency when `xen,static-mem` and `memory` are both
   xen/arch/arm/domain_build.c | 37 +++++++++++++++++++++++++++++++---
   1 file changed, 31 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 282416e74d..4166d7993c 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2424,23 +2424,47 @@ static int __init construct_domU(struct domain
       struct kernel_info kinfo = {};
       int rc;
-    u64 mem;
+    u64 mem, static_mem_size = 0;
+    const struct dt_property *prop;
+    bool static_mem = false;
+    d->max_pages = ~0U;
+    /*
+     * Guest RAM could be of static memory from static allocation,
+     * which will be specified through "xen,static-mem" phandle.
+     */
+    prop = dt_find_property(node, "xen,static-mem", NULL);
+    if ( prop )
+    {
+        static_mem = true;
+        /* static_mem_size = allocate_static_memory(...); */
+        BUG();
+    }

I would prefer if the static memory is allocated close to
allocate_memory() below. AFAICT, the reason you allocate here is because you
want to have the property "memory" optional.

However, I am not entirely convinced this is a good idea to make optional. It
would be easier for a reader to figure out from the device-tree how much
memory we give to the guest.

Hmmm, now I think maybe I understand wrongly what you suggested in v1.
Could we allocate the memory as we parse?
I just simply think it means the code sequence, putting allocation immediately
after parsing. ;/

I really meant "parse and allocate" in a iteration. My comment this time is the parsing/allocation for static memory should happen close to when the allocation for dynamic memory is done.

After all you are allocating memory for domain, so it makes more sense to have the two different way to allocate cloe to each other.

Re-investigating the docs on "memory":

- memory

     A 64-bit integer specifying the amount of kilobytes of RAM to
     allocate to the guest.
If you prefer "memory" mandate, then tbh, it will make the code
here more easily-read, no ifs.
But maybe I shall put more info on docs to clarify that even though user using
"xen, static-mem" to refer to static memory allocation, they shall still use
"memory" property to tell how much memory we give to the guest.

Hmm... I am not sure this is necessary, the property "memory" is not marked as optional even after your patch.

However, I would clarify that all the memory should either be allocated statically or dynamically...


Julien Grall



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