On 29/05/2019 09:24, Paolo Bonzini wrote:
On 24/05/19 09:56, Tao Xu wrote:
+7.19 KVM_CAP_ENABLE_USR_WAIT_PAUSE
+
+Architectures: x86
+Parameters: args[0] whether feature should be enabled or not
+
+With this capability enabled, a VM can use UMONITOR, UMWAIT and TPAUSE
+instructions. If the instruction causes a delay, the amount of
+time delayed is called here the physical delay. The physical delay is
+first computed by determining the virtual delay (the time to delay
+relative to the VM’s timestamp counter). Otherwise, UMONITOR, UMWAIT
+and TPAUSE cause an invalid-opcode exception(#UD).
+
There is no need to make it a capability. You can just check the guest
CPUID and see if it includes X86_FEATURE_WAITPKG.
Paolo
Thank you Paolo, but I have another question. I was wondering if it is
appropriate to enable X86_FEATURE_WAITPKG when QEMU uses "-overcommit
cpu-pm=on"? Or just enable X86_FEATURE_WAITPKG when QEMU add the feature
"-cpu host,+waitpkg"? User wait instructions is the wait or pause
instructions may be executed at any privilege level, but can use
IA32_UMWAIT_CONTROL to set the maximum time.
