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The GSI callback (and later PCI_INTX) is a level triggered interrupt. It is asserted when an event channel is delivered to vCPU0, and is supposed to be cleared when the vcpu_info->evtchn_upcall_pending field for vCPU0 is cleared again. Thankfully, Xen does *not* assert the GSI if the guest sets its own evtchn_upcall_pending field; we only need to assert the GSI when we have delivered an event for ourselves. So that's the easy part, kind of. There's a slight complexity in that we need to hold the BQL before we can call qemu_set_irq(), and we definitely can't do that while holding our own port_lock (because we'll need to take that from the qemu-side functions that the PV backend drivers will call). So if we end up wanting to set the IRQ in a context where we *don't* already hold the BQL, defer to a BH. However, we *do* need to poll for the evtchn_upcall_pending flag being cleared. In an ideal world we would poll that when the EOI happens on the PIC/IOAPIC. That's how it works in the kernel with the VFIO eventfd pairs — one is used to trigger the interrupt, and the other works in the other direction to 'resample' on EOI, and trigger the first eventfd again if the line is still active. However, QEMU doesn't seem to do that. Even VFIO level interrupts seem to be supported by temporarily unmapping the device's BARs from the guest when an interrupt happens, then trapping *all* MMIO to the device and sending the 'resample' event on *every* MMIO access until the IRQ is cleared! Maybe in future we'll plumb the 'resample' concept through QEMU's irq framework but for now we'll do what Xen itself does: just check the flag on every vmexit if the upcall GSI is known to be asserted. Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Reviewed-by: Paul Durrant <paul@xen.org> |
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| .. | ||
| hax | ||
| hvf | ||
| kvm | ||
| nvmm | ||
| tcg | ||
| whpx | ||
| arch_dump.c | ||
| arch_memory_mapping.c | ||
| cpu-dump.c | ||
| cpu-internal.h | ||
| cpu-param.h | ||
| cpu-qom.h | ||
| cpu-sysemu.c | ||
| cpu.c | ||
| cpu.h | ||
| gdbstub.c | ||
| helper.c | ||
| helper.h | ||
| host-cpu.c | ||
| host-cpu.h | ||
| Kconfig | ||
| machine.c | ||
| meson.build | ||
| monitor.c | ||
| ops_sse.h | ||
| ops_sse_header.h | ||
| sev-sysemu-stub.c | ||
| sev.c | ||
| sev.h | ||
| shift_helper_template.h | ||
| svm.h | ||
| trace-events | ||
| trace.h | ||
| xsave_helper.c | ||