Re: [Qemu-devel] [PATCH 1/4] s390/kvm: Handle hosts not supporting s390-virtio.

[Alexander Graf]

On 07.08.2012, at 16:52, Cornelia Huck wrote:

> Running under a kvm host does not necessarily imply the presence of
> a page mapped above the main memory with the virtio information;
> however, the code includes a hard coded access to that page.
> 
> Instead, check for the presence of the page and exit gracefully
> before we hit an addressing exception if it does not exist.
> 
> Signed-off-by: Cornelia Huck <address@hidden>
> ---
> drivers/s390/kvm/kvm_virtio.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
> index 47cccd5..408447c 100644
> --- a/drivers/s390/kvm/kvm_virtio.c
> +++ b/drivers/s390/kvm/kvm_virtio.c
> @@ -418,6 +418,21 @@ static void kvm_extint_handler(struct ext_code ext_code,
>       }
> }
> 
> +static int __init test_devices_support(void)

Today we know what this function does, but the next person running into it has 
no clue. Maybe add a nice description here that you're trying to access memory 
above ram? (is this even what you're doing here? my s390 asm is slightly rusty) 
:)

Alex

> +{
> +     int ccode = -EIO;
> +
> +     asm volatile(
> +             "0:     cli     0(%1),0\n"
> +             "       ipm     %0\n"
> +             "       srl     %0,28\n"
> +             "1:\n"
> +             EX_TABLE(0b,1b)
> +             : "+d" (ccode)
> +             : "a" (kvm_devices)
> +             : "cc");
> +     return ccode;
> +}
> /*
>  * Init function for virtio
>  * devices are in a single page above top of "normal" mem
> @@ -443,6 +458,12 @@ static int __init kvm_devices_init(void)
>       }
> 
>       kvm_devices = (void *) real_memory_size;
> +     if (test_devices_support() < 0) {
> +             vmem_remove_mapping(real_memory_size, PAGE_SIZE);
> +             root_device_unregister(kvm_root);
> +             /* No error. */
> +             return 0;
> +     }
> 
>       INIT_WORK(&hotplug_work, hotplug_devices);
> 
> -- 
> 1.7.11.4
>