Xen provides support for injecting interrupts to the guests via the
HYPERVISOR_dm_op() hypercall. The same is used by the Virtio based
device backend implementations, in an inefficient manner currently.
Generally, the Virtio backends are implemented to work with the Eventfd
based mechanism. In order to make such backends work with Xen, another
software layer needs to poll the Eventfds and raise an interrupt to the
guest using the Xen based mechanism. This results in an extra context
switch.
This is not a new problem in Linux though. It is present with other
hypervisors like KVM, etc. as well. The generic solution implemented in
the kernel for them is to provide an IOCTL call to pass the interrupt
details and eventfd, which lets the kernel take care of polling the
eventfd and raising of the interrupt, instead of handling this in user
space (which involves an extra context switch).
This patch adds support to inject a specific interrupt to guest using
the eventfd mechanism, by preventing the extra context switch.
Inspired by existing implementations for KVM, etc..
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
V2.1->V3
- No changes
V2->V2.1
- Select EVENTFD from Kconfig
V1->V2:
- Improve error handling.
- Remove the unnecessary usage of list_for_each_entry_safe().
- Restrict the use of XEN_DMOP_set_irq_level to only ARM64.
drivers/xen/Kconfig | 1 +
drivers/xen/privcmd.c | 276 ++++++++++++++++++++++++++++++++++++-
include/uapi/xen/privcmd.h | 14 ++
3 files changed, 289 insertions(+), 2 deletions(-)
diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
index d5d7c402b651..7967393c55a4 100644
--- a/drivers/xen/Kconfig
+++ b/drivers/xen/Kconfig
@@ -261,6 +261,7 @@ config XEN_SCSI_BACKEND
config XEN_PRIVCMD
tristate "Xen hypercall passthrough driver"
depends on XEN
+ select EVENTFD
Attachment:
OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key
Attachment:
OpenPGP_signature
Description: OpenPGP digital signature