vmm: Only return from reset driven I/O once event received #5645
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
The reset system is asynchronous with an I/O event (PIO or MMIO) for ACPI/i8042/CMOS triggering a write to the reset_evt event handler. The VMM thread will pick up this event on the VMM main loop and then trigger a shutdown in the CpuManager. However since there is some delay between the CPU threads being marked to be killed (through the CpuManager::cpus_kill_signalled bool) it is possible for the guest vCPU that triggered the exit to be re-entered when the vCPU KVM_RUN is called after the I/O exit is completed. This is undesirable and in particular the Linux kernel will attempt to jump to real mode after a CMOS based exit - this is unsupported in nested KVM on AMD on Azure and will trigger an error in KVM_RUN. Solve this problem by spinning in the device that has triggered the reset until the vcpus_kill_signalled boolean has been updated indicating that the VMM thread has received the event and called CpuManager::shutdown(). In particular if this bool is set then the vCPU threads will not re-enter the guest. Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
rbradford
force-pushed
the
2023-08-03-spin-waiting-for-reset-event-received
branch
from
a0b1cff
to
456ff9e
Compare
Merged
likebreath
approved these changes
Aug 4, 2023
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The reset system is asynchronous with an I/O event (PIO or MMIO) for
ACPI/i8042/CMOS triggering a write to the reset_evt event handler. The
VMM thread will pick up this event on the VMM main loop and then trigger
a shutdown in the CpuManager. However since there is some delay between
the CPU threads being marked to be killed (through the
CpuManager::cpus_kill_signalled bool) it is possible for the guest vCPU
that triggered the exit to be re-entered when the vCPU KVM_RUN is called
after the I/O exit is completed.
This is undesirable and in particular the Linux kernel will attempt to
jump to real mode after a CMOS based exit - this is unsupported in
nested KVM on AMD on Azure and will trigger an error in KVM_RUN.
Solve this problem by spinning in the device that has triggered the
reset until the vcpus_kill_signalled boolean has been updated
indicating that the VMM thread has received the event and called
CpuManager::shutdown(). In particular if this bool is set then the vCPU
threads will not re-enter the guest.
Signed-off-by: Rob Bradford rbradford@rivosinc.com