On 2/26/19 6:24 AM, Paul Mackerras wrote:
> On Fri, Feb 22, 2019 at 12:28:30PM +0100, Cédric Le Goater wrote:
>> These controls will be used by the H_INT_SET_QUEUE_CONFIG and
>> H_INT_GET_QUEUE_CONFIG hcalls from QEMU. They will also be used to
>> restore the configuration of the XIVE EQs in the KVM device and to
>> capture the internal runtime state of the EQs. Both 'get' and 'set'
>> rely on an OPAL call to access from the XIVE interrupt controller the
>> EQ toggle bit and EQ index which are updated by the HW when event
>> notifications are enqueued in the EQ.
>>
>> The value of the guest physical address of the event queue is saved in
>> the XIVE internal xive_q structure for later use. That is when
>> migration needs to mark the EQ pages dirty to capture a consistent
>> memory state of the VM.
>>
>> To be noted that H_INT_SET_QUEUE_CONFIG does not require the extra
>> OPAL call setting the EQ toggle bit and EQ index to configure the EQ,
>> but restoring the EQ state will.
>
> [snip]
>
>> +/* Layout of 64-bit eq attribute */
>> +#define KVM_XIVE_EQ_PRIORITY_SHIFT 0
>> +#define KVM_XIVE_EQ_PRIORITY_MASK 0x7
>> +#define KVM_XIVE_EQ_SERVER_SHIFT 3
>> +#define KVM_XIVE_EQ_SERVER_MASK 0xfffffff8ULL
>> +
>> +/* Layout of 64-bit eq attribute values */
>> +struct kvm_ppc_xive_eq {
>> + __u32 flags;
>> + __u32 qsize;
>> + __u64 qpage;
>> + __u32 qtoggle;
>> + __u32 qindex;
>> + __u8 pad[40];
>> +};
>
> This is confusing. What's the difference between an "eq attribute"
> and an "eq attribute value"? Is the first actually a queue index or
> a queue identifier?
The "attribute" qualifier comes from the {get,set,has}_addr methods
of the KVM device. But it is not a well chosen name for the group
KVM_DEV_XIVE_GRP_EQ_CONFIG.
I should be using "eq identifier" and "eq values" or "eq state".
> Also, the kvm_ppc_xive_eq is not 64 bits, so the comment above it is
> wrong. Maybe you meant "64-byte"?
That was a bad copy paste. I have padded the structure to twice the size
of the XIVE END (the XIVE EQ descriptor in HW) which size is 32 bytes.
I thought that one extra u64 was not enough room for future.
>
> [snip]
>
>> + page = gfn_to_page(kvm, gpa_to_gfn(kvm_eq.qpage));
>> + if (is_error_page(page)) {
>> + pr_warn("Couldn't get guest page for %llx!\n", kvm_eq.qpage);
>> + return -ENOMEM;
>> + }
>> + qaddr = page_to_virt(page) + (kvm_eq.qpage & ~PAGE_MASK);
>
> Isn't this assuming that we can map the whole queue with a single
> gfn_to_page? That would only be true if kvm_eq.qsize <= PAGE_SHIFT.
> What happens if kvm_eq.qsize > PAGE_SHIFT?
Ah yes. Theoretically, it should not happen because we only advertise
64K in the DT for the moment. I should at least add a check. So I will
change the helper xive_native_validate_queue_size() to return -EINVAL
for other page sizes.
Do you think it would be complex to support XIVE EQs using a page larger
than the default one on the guest ?
Thanks,
C.
>
> Paul.
>
