Re: [PATCH 09/19] KVM: PPC: Book3S HV: add a SET_SOURCE control to the XIVE native device

["Cédric Le Goater" <clg@kaod.org>]

On 2/5/19 6:35 AM, David Gibson wrote:
> On Mon, Feb 04, 2019 at 08:07:20PM +0100, Cédric Le Goater wrote:
>> On 2/4/19 5:57 AM, David Gibson wrote:
>>> On Mon, Jan 07, 2019 at 07:43:21PM +0100, Cédric Le Goater wrote:
> [snip]
>>>> +		sb = kvmppc_xive_create_src_block(xive, irq);
>>>> +		if (!sb) {
>>>> +			pr_err("Failed to create block...\n");
>>>> +			return -ENOMEM;
>>>> +		}
>>>> +	}
>>>> +	state = &sb->irq_state[idx];
>>>> +
>>>> +	if (get_user(val, ubufp)) {
>>>> +		pr_err("fault getting user info !\n");
>>>> +		return -EFAULT;
>>>> +	}
>>>> +
>>>> +	/*
>>>> +	 * If the source doesn't already have an IPI, allocate
>>>> +	 * one and get the corresponding data
>>>> +	 */
>>>> +	if (!state->ipi_number) {
>>>> +		state->ipi_number = xive_native_alloc_irq();
>>>> +		if (state->ipi_number == 0) {
>>>> +			pr_err("Failed to allocate IRQ !\n");
>>>> +			return -ENOMEM;
>>>> +		}
>>>
>>> Am I right in thinking this is the point at which a specific guest irq
>>> number gets bound to a specific host irq number?
>>
>> yes. the XIVE IRQ state caches this information and 'state' should be 
>> protected before being assigned, indeed ... The XICS-over-XIVE device
>> also has the same race issue.
>>
>> It's not showing because where initializing the KVM device sequentially
>> from QEMU and only once.
> 
> Ok.
> 
> So, for the passthrough case, what's the point at which we know that a
> particular guest interrupt needs to be bound to a specific real
> hardware interrupt, rather than a generic IPI?

when the guest driver requests MSIs, VFIO requests a mapping of the 
HW irqs in the guest IRQ space. This is very briefly said as VFIO is 
a huge framework. 

Patch 18 adds some initial support to handle the ESB pages but this 
should be done at the QEMU level.

C.