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HYPERVISOR_console_io + CONSOLEIO_write needs COPY_flush_dcache
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>
- Date: Wed, 10 Jun 2020 08:13:50 +0000
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- Thread-topic: HYPERVISOR_console_io + CONSOLEIO_write needs COPY_flush_dcache
Hello,
While adding support for para-virtualized block device in u-boot
I faced an issue with HYPERVISOR_console_io + CONSOLEIO_write.
I tried to use the hypercall during MMU setup stage while enabling data cache
on arm64 platform (e.g. data cache is not yet enabled) and saw in guest's
console
either old data or some sort of garbage. Printing constant strings, just like
mini-os
does on boot, works as expected. So, looking at the Xen code [1] it seems
that we should copy guest's buffer with COPY_flush_dcache set in this case
as (usually?) this hypercall is used in guest's code which doesn't have any
other means to print yet, e.g. early printk case.
If my understanding of the issue correct then I can probably prepare a patch.
Thank you,
Oleksandr
[1]
https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/drivers/char/console.c;h=56e24821b2f8d2b9bfb99d2acb721b06277834ce;hb=refs/heads/master#l597
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