On Tue, Dec 10, 2013 at 04:49:19PM +0100, Alexander Graf wrote:
On 10.12.2013, at 05:23, Anup Patel anup@brainfault.org wrote:
On Tue, Dec 10, 2013 at 7:43 AM, Alexander Graf agraf@suse.de wrote:
On 25.11.2013, at 16:49, Anup Patel anup.patel@linaro.org wrote:
Currently, we don't have an exit reason for VM reset emulation in user space hence this patch adds exit reason KVM_EXIT_RESET for this purpose.
This newly added KVM_EXIT_RESET will be used by KVM arm/arm64 in-kernel PSCI support to reset VMs.
Signed-off-by: Anup Patel anup.patel@linaro.org Signed-off-by: Pranavkumar Sawargaonkar pranavkumar@linaro.org
include/uapi/linux/kvm.h | 1 + 1 file changed, 1 insertion(+)
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index 902f124..64a04cc 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -171,6 +171,7 @@ struct kvm_pit_config { #define KVM_EXIT_WATCHDOG 21 #define KVM_EXIT_S390_TSCH 22 #define KVM_EXIT_EPR 23 +#define KVM_EXIT_RESET 24
I have to admit that I'm not particularly happy with the exit name. It's not obvious from the name under which circumstances it gets triggered. Does it get triggered when a core level reset happens? Does it get triggered when a system level reset happened? When the guest requests one?
The KVM_EXIT_RESET gets triggered when system level reset is initiated by VCPU. For arm/arm64, this is through SYSTEM_RESET PSCI call. In KVM x86 SVM/VMX, we have KVM_EXIT_SHUTDOWN being used for system shutdown which we have re-used for arm/arm64.
Yeah, that name already did mislead you once :).
KVM_EXIT_SHUTDOWN happens on
- triple fault
- CPU internal severe problems
the latter is defined as:
In contrast, an error that cannot be contained and is of such severity that it has compromised the continued operation of a processor core requires immediate action to terminate system processing and may result in a hardware-enforced shutdown. In the shutdown state, the execution of instructions by that processor core is halted. See Section 8.2.9 “#DF—Double-Fault Exception (Vector 8)” on page 220 for a description of the shutdown processor state.
Triple faults are used commonly in 286 code to switch from PG to real mode. So they _have_ to be emulated as core reset. Otherwise you break old guests.
However, the scope of this exit is definitely vcpu wide. What you are looking for is a system wide notification. Commonly this happens through MMIO, but I can see why you wouldn't want that with PSCI interpreted in the kernel. That's why I asked you to create a completely new one to not add up the the confusion.
Did you grab this documentation from somewhere that I can't find with grep, or did you just come up with it?
Shouldn't we have all exit reasons documented in Documentation/virtual/kvm/... ?
I know what it does, but I find the name too generic for what it is. What you're really doing is introduce a new communication channel in parallel to MMIO / PIO / HCALL which is only used for system level reset / shutdown today.
Can we treat it as such? Could you please make this a common exit number that's called something like
KVM_EXIT_SYSTEM_EVENT
with a parameter that can either be TRIGGER_SHUTDOWN or TRIGGER_RESET.
That way it's obvious what's going on and people don't get confused.
I don't foresee any system level operations other than SHUTDOWN and RESET to be handled from KVM in-kernel code but I might be wrong.
The good but about the EXIT_SYSTEM_EVENT is that it's immediately obvious that we're not talking about a vcpu local event. But I'm open to better names.
May be we can rename KVM_EXIT_SHUTDOWN and KVM_EXIT_RESET to KVM_EXIT_SYSTEM_SHUTDOWN and KVM_EXIT_SYSTEM_RESET ??
You definitely can not rename KVM_EXIT_SHUTDOWN. It's part of the KVM API. In fact, I think it's a bad idea to even reuse the name as it clearly works on vcpu level.
-Christoffer