On 05/27/2015 05:06 AM, Steve Rutherford wrote:
On Sun, May 24, 2015 at 07:46:03PM +0300, Avi Kivity wrote:
On 05/13/2015 04:47 AM, Steve Rutherford wrote:
Adds KVM_EXIT_IOAPIC_EOI which passes the interrupt vector up to
userspace.
Uses a per VCPU exit bitmap to decide whether or not the IOAPIC needs
to be informed (which is identical to the EOI_EXIT_BITMAP field used
by modern x86 processors, but can also be used to elide kvm IOAPIC EOI
exits on older processors).
[Note: A prototype using ResampleFDs found that decoupling the EOI
>from the VCPU's thread made it possible for the VCPU to not see a
recent EOI after reentering the guest. This does not match real
hardware.]
Compile tested for Intel x86.
Signed-off-by: Steve Rutherford <srutherford@xxxxxxxxxx>
---
Documentation/virtual/kvm/api.txt | 10 ++++++++++
arch/x86/include/asm/kvm_host.h | 3 +++
arch/x86/kvm/lapic.c | 9 +++++++++
arch/x86/kvm/x86.c | 11 +++++++++++
include/linux/kvm_host.h | 1 +
include/uapi/linux/kvm.h | 5 +++++
6 files changed, 39 insertions(+)
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 0744b4e..dd92996 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3285,6 +3285,16 @@ Valid values for 'type' are:
*/
__u64 kvm_valid_regs;
__u64 kvm_dirty_regs;
+
+ /* KVM_EXIT_IOAPIC_EOI */
+ struct {
+ __u8 vector;
+ } eoi;
+
+Indicates that an eoi of a level triggered IOAPIC interrupt on vector has
+occurred, which should be handled by the userspace IOAPIC. Triggers when
+the Irqchip has been split between userspace and the kernel.
+
The ioapic is a global resource, so it doesn't make sense for
information about it to be returned in a per-vcpu structure
EOI exits are a per-vcpu behavior, so this doesn't seem all that strange.
(or to block the vcpu while it is being processed).
Blocking doesn't feel clean, but doesn't seem all that bad, given
that these operations are relatively rare on modern configurations.
Agree, maybe the realtime people have an interest here.
The way I'd model it is to emulate the APIC bus that connects local
APICs and the IOAPIC, using a socket pair. When the user-space
ioapic wants to inject an interrupt, it sends a message to the local
APICs which then inject it, and when it's ack'ed the EOI is sent
back on the same bus.
Although I'm not certain about this, it sounds to me like this would
require a kernel thread to be waiting (in some way) on this socket, which
seems rather heavy handed.
It's been a while since I did kernel programming, but I think you can
queue a callback to be called when an I/O is ready, and not require a
thread. IIRC we do that with irqfd to cause an interrupt to be injected.
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