Re: [Qemu-devel] [PATCH 3/6] kvm: workaround a possible KVM bug when using KVM_MEM_READONLY

[Jordan Justen]

On Mon, Apr 29, 2013 at 3:29 AM, Jan Kiszka <address@hidden> wrote:
> On 2013-04-28 10:32, Jordan Justen wrote:
>> On a Linux 3.8.0 based kernel, I occasionally saw a situation
>> where the memory region would continue to trap on memory
>> read even though KVM_MEM_READONLY was set.
>
> Only 3.8.0? Did you bisect the issue down to the causing commit? Is it
> fixed in later versions?

I'm sorry, I have not tried to bisect, nor have I tried a newer kernel version.

Speculating a bit, it seems that a trap to the region might cause the
issue. This is what happens in the failing case:
* Disable mem region
* Trap on access to region
* Enable readonly region
* Next read access will trap when it shouldn't

Here is the what happen with the work-around:
* Disable mem region
* Trap on access to region
* (Re-)disable mem region (work-around adds this)
* Enable readonly region
* Next read access will not trap (proper behavior)

-Jordan