Re: [PATCH kvmtool 2/4] arm/fdt.c: Warn if MMIO device doesn't provide a node generator

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Andre,

On 6/10/21 5:13 PM, Andre Przywara wrote:
> On Wed,  9 Jun 2021 19:38:10 +0100
> Alexandru Elisei <alexandru.elisei@arm.com> wrote:
>
>> Print a more helpful warning when a MMIO device hasn't set a function to
>> generate an FDT instead of causing a segmentation fault by dereferencing a
>> NULL pointer.
> Not calling generate_mmio_fdt_nodes() if it's NULL is certainly a good
> idea, but how did you trigger it?

I was able to trigger it when I was hacking a custom MMIO device emulation to test
some behaviour in KVM.

> Because I am wondering whether every MMIO device needs to have an DT
> generator? And if that's not the case, a warning might be already too
> much.

I don't know how the guest will be able to discover the device if it's not in the
DT, that's why I put the warning. If there are devices which can be discovered by
the guest when they are missing from the DT, then I'll drop the warning.

Thanks,

Alex

>
> So either just drop a print at all or use pr_info()/pr_debug()?
>
> Cheers,
> Andre
>
>> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
>> ---
>>  arm/fdt.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/arm/fdt.c b/arm/fdt.c
>> index 02091e9e0bee..06287a13e395 100644
>> --- a/arm/fdt.c
>> +++ b/arm/fdt.c
>> @@ -171,7 +171,12 @@ static int setup_fdt(struct kvm *kvm)
>>  	dev_hdr = device__first_dev(DEVICE_BUS_MMIO);
>>  	while (dev_hdr) {
>>  		generate_mmio_fdt_nodes = dev_hdr->data;
>> -		generate_mmio_fdt_nodes(fdt, dev_hdr, generate_irq_prop);
>> +		if (generate_mmio_fdt_nodes) {
>> +			generate_mmio_fdt_nodes(fdt, dev_hdr, generate_irq_prop);
>> +		} else {
>> +			pr_warning("Missing FDT node generator for MMIO device %d",
>> +				   dev_hdr->dev_num);
>> +		}
>>  		dev_hdr = device__next_dev(dev_hdr);
>>  	}
>>