Hi Stefano,
On 09/11/2021 22:29, Stefano Stabellini wrote:
From: Stefano Stabellini <[email protected]>
allocate_bank_memory can be called with a tot_size of zero.
Please add some details how this can be called with tot_size == 0.
AFAIU, this happens when creating the second bank.
In that
case, don't create an empty memory bank, just return immediately without
error. Otherwise a zero-sized memory bank will be added to the domain
device tree.
There are actually DTs out with zero-size memory bank (see [1]) and,
AFAIR, Linux is able to cope with it.
Instead, it looks like the issue is some part of Xen may fall over if
one of the bank is zero-sized. But from the earlier discussion [2], this
is just latent. So I think this should be clarified in the commit message.
Fixes: f2931b4233ec "xen/arm: introduce allocate_memory"
Signed-off-by: Stefano Stabellini <[email protected]>
---
xen/arch/arm/domain_build.c | 3 +++
1 file changed, 3 insertions(+)
Please explain why you would like to include it in 4.16. In particular
that as I wrote above, Linux is able to cope with zero-size memory bank.
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 9e92b640cd..578ea80e40 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -395,6 +395,9 @@ static bool __init allocate_bank_memory(struct domain *d,
struct membank *bank;
unsigned int max_order = ~0;
+ if ( tot_size == 0 )
+ return true;
One may argue this is a bug. So I think it would be worth explaining in
a comment that we can safely ignore empty bank and why.
Cheers,
[1] commit 5a37207df52066efefe419c677b089a654d37afc
Author: Julien Grall <[email protected]>
Date: Fri Sep 18 18:11:16 2020 +0100
xen/arm: bootfdt: Ignore empty memory bank
At the moment, Xen will stop processing the Device Tree if a memory
bank is empty (size == 0).
Unfortunately, some of the Device Tree (such as on Colibri imx8qxp)
may contain such a bank. This means Xen will not be able to boot
properly.
Relax the check to just ignore the banks. FWIW this also seems to
be the
behavior adopted by Linux.
[2] alpine.DEB.2.22.394.2111091423020.440530@ubuntu-linux-20-04-desktop
--
Julien Grall
