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authorWanpeng Li <wanpengli@tencent.com>2018-03-12 14:53:02 +0300
committerPaolo Bonzini <pbonzini@redhat.com>2018-03-17 00:03:51 +0300
commit4d5422cea3b61f158d58924cbb43feada456ba5c (patch)
tree0657ac655c54892dd6498d8e20b89380255d592a /Documentation/virtual
parent4956aa3b8b59e336b77f1df0ac7ce1a94c0265f2 (diff)
downloadlinux-4d5422cea3b61f158d58924cbb43feada456ba5c.tar.xz
KVM: X86: Provide a capability to disable MWAIT intercepts
Allowing a guest to execute MWAIT without interception enables a guest to put a (physical) CPU into a power saving state, where it takes longer to return from than what may be desired by the host. Don't give a guest that power over a host by default. (Especially, since nothing prevents a guest from using MWAIT even when it is not advertised via CPUID.) Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Jan H. Schönherr <jschoenh@amazon.de> Signed-off-by: Wanpeng Li <wanpengli@tencent.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virtual')
-rw-r--r--Documentation/virtual/kvm/api.txt27
1 files changed, 18 insertions, 9 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 786c1b4ecb59..744a202cca31 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -4358,6 +4358,24 @@ enables QEMU to build error log and branch to guest kernel registered
machine check handling routine. Without this capability KVM will
branch to guests' 0x200 interrupt vector.
+7.13 KVM_CAP_X86_DISABLE_EXITS
+
+Architectures: x86
+Parameters: args[0] defines which exits are disabled
+Returns: 0 on success, -EINVAL when args[0] contains invalid exits
+
+Valid bits in args[0] are
+
+#define KVM_X86_DISABLE_EXITS_MWAIT (1 << 0)
+
+Enabling this capability on a VM provides userspace with a way to no
+longer intercept some instructions for improved latency in some
+workloads, and is suggested when vCPUs are associated to dedicated
+physical CPUs. More bits can be added in the future; userspace can
+just pass the KVM_CHECK_EXTENSION result to KVM_ENABLE_CAP to disable
+all such vmexits.
+
+
8. Other capabilities.
----------------------
@@ -4470,15 +4488,6 @@ reserved.
Both registers and addresses are 64-bits wide.
It will be possible to run 64-bit or 32-bit guest code.
-8.8 KVM_CAP_X86_GUEST_MWAIT
-
-Architectures: x86
-
-This capability indicates that guest using memory monotoring instructions
-(MWAIT/MWAITX) to stop the virtual CPU will not cause a VM exit. As such time
-spent while virtual CPU is halted in this way will then be accounted for as
-guest running time on the host (as opposed to e.g. HLT).
-
8.9 KVM_CAP_ARM_USER_IRQ
Architectures: arm, arm64