From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: ioeventfd usage in KVM
Date: Fri, 12 Mar 2010 09:43:45 +0200
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References: <8286e4ee1003112108j4a3a477dq4abb1b8624319125@mail.gmail.com>
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Cc: KVM General <kvm@vger.kernel.org>
To: Cam Macdonell <cam@cs.ualberta.ca>
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On 03/12/2010 07:08 AM, Cam Macdonell wrote:
>
> +    s->ivshmem_mmio_io_addr = cpu_register_io_memory(ivshmem_mmio_read,
> +                                    ivshmem_mmio_write, s);
> +    /* region for registers*/
> +    pci_register_bar(&d->dev, 0, 0x100,
> +                           PCI_BASE_ADDRESS_SPACE_MEMORY, ivshmem_mmio_map);
>    

You've selected the memory address space here.

> my basic attempt looks like this:
>
>      struct kvm_ioeventfd ked;
>
>      ked.addr = s->otheraddr + Doorbell;
>      ked.len = 4;
>      ked.flags = KVM_IOEVENTFD_FLAG_PIO;
>      ked.fd = an_eventfd;
>      ret = kvm_vm_ioctl(kvm_state, KVM_IOEVENTFD,&ked);
>    

But the PIO address space here.

> but when the guest writes to the offset of Doorbell, I cannot see any
> action (via a select on the fd).  Is there something obviously wrong
> that I'm doing?
>    

Yes - they must match.  Not PIO is faster on x86 but nonexistant elsewhere.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.