On 2018-08-17 12:55, Ralf Ramsauer wrote:
Hi,
On 08/17/2018 09:19 AM, Jan Kiszka wrote:
Hi Ralf,
this seems to work, despite the comment. Do you remember why we have
that restriction?
diff --git a/hypervisor/include/jailhouse/header.h
b/hypervisor/include/jailhouse/header.h
index 518bc5cb..9dc76f81 100644
--- a/hypervisor/include/jailhouse/header.h
+++ b/hypervisor/include/jailhouse/header.h
@@ -43,7 +43,7 @@ struct jailhouse_virt_console {
unsigned int tail;
/* current implementation requires the size of the content to be a
* power of two */
- char content[2048];
+ char content[4096 - 2 * sizeof(unsigned int)];
That's been a while… I remember that there have been some arguments, but
it's in deed not obvious by looking at the code…
[grabs out an old review of a previous revision]
Here's the rationale: [1]
Writer side increments the tail pointer without modulo operations
(hv/printk.c:41). If it's not a power of two, it will fail as we get
misaligned once we overflow the unsigned int. AFAICT, on reader side
we're relying on that alignement (main.c:281).
We should improve on documenting that inline.
This issue should become visible, once the tail pointer overflows 32
bit. You could test this situation by offsetting the initialisation of
head/tail.
Right. I was hoping to "cheaply" increase the buffer because it already
overflows during enable on the NUC6CAY. But it's probably easier to
expand it by adding real pages.
Jan
--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux
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