06.07.2021 23:29, Maxim Levitsky пишет:
On Tue, 2021-07-06 at 15:06 +0300, stsp wrote:
06.07.2021 14:49, Maxim Levitsky пишет:
Now about the KVM's userspace API where this is exposed:
I see now too that KVM_SET_REGS clears the pending exception.
This is new to me and it is IMHO *wrong* thing to do.
However I bet that someone somewhere depends on this,
since this behavior is very old.
What alternative would you suggest?
Check for ready_for_interrupt_injection
and never call KVM_SET_REGS if it indicates
"not ready"?
But what if someone calls it nevertheless?
Perhaps return an error from KVM_SET_REGS
if exception is pending? Also KVM_SET_SREGS
needs some treatment here too, as it can
also be called when an exception is pending,
leading to problems.
As I explained you can call KVM_GET_VCPU_EVENTS before calling
KVM_SET_REGS and then call KVM_SET_VCPU_EVENTS with the struct
that was filled by KVM_GET_VCPU_EVENTS.
That will preserve all the cpu events.
The question is different.
I wonder how _should_ the KVM
API behave when someone calls
KVM_SET_REGS/KVM_SET_SREGS
while the exception is pending.
This is currently not handled properly.
We can add/fix the indication with
ready_for_interrupt_injection,
but someone will ignore that
indication, so some handling
(like returning an error) should
be added.
So what would you propose the
KVM_SET_REGS should do if it is
called when an exception is pending?
The question is here because
currently KVM_SET_REGS and
KVM_SET_SREGS handle that differently:
one is trying to cancel the pending
excpetion, and the other one
does nothing, but both are wrong.
