I have been pulling my hair out for 4 hours today with this extremely odd issue. I'm trying to implement MSI-X for my VirtIO network driver, but the interrupts are never triggered. Instead, when running QEMU with "-d guest_errors", it will warn me about an "Invalid access at addr 0xFEE00000, size 4, region '(null)', reason: rejected", triggered every time the network device would trigger MSI-X (after transmitting a packet and upon receiving one). I have no clue what causes this issue; it seems like the given Message Address is correct (based on other examples I found online), but still it doesn't work.
This is the code to set the MSI-X table entry:
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entry->msg_addr = 0xFEE00000 | (this_cpu->cpu_id << 12); // cpu_id is the LAPIC cpu_id which is 0 in my singlecore test; the LAPIC ID is also 0
entry->msg_data = int_number; // 64 in this case, tried other values without success
entry->vec_ctrl = 0; // unmasking
I think my LAPIC works fine, since I have set up the timer which fires regular interrupts. I have added the interrupt vectors to my IDT, and their ISR should log output. But clearly, they are not triggered. Are there any specific requirements to my LAPIC setup to get MSI-X working?
What is my mistake here? Anything obvious I'm missing?