KVM: Per-vcpu inodes
Allocate a distinct inode for every vcpu in a VM. This has the following
benefits:
- the filp cachelines are no longer bounced when f_count is incremented on
every ioctl()
- the API and internal code are distinctly clearer; for example, on the
KVM_GET_REGS ioctl, there is no need to copy the vcpu number from
userspace and then copy the registers back; the vcpu identity is derived
from the fd used to make the call
Right now the performance benefits are completely theoretical since (a) we
don't support more than one vcpu per VM and (b) virtualization hardware
inefficiencies completely everwhelm any cacheline bouncing effects. But
both of these will change, and we need to prepare the API today.
Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index d6e6635..7c9a400 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -52,11 +52,10 @@
/* for KVM_RUN */
struct kvm_run {
/* in */
- __u32 vcpu;
__u32 emulated; /* skip current instruction */
__u32 mmio_completed; /* mmio request completed */
__u8 request_interrupt_window;
- __u8 padding1[3];
+ __u8 padding1[7];
/* out */
__u32 exit_type;
@@ -111,10 +110,6 @@
/* for KVM_GET_REGS and KVM_SET_REGS */
struct kvm_regs {
- /* in */
- __u32 vcpu;
- __u32 padding;
-
/* out (KVM_GET_REGS) / in (KVM_SET_REGS) */
__u64 rax, rbx, rcx, rdx;
__u64 rsi, rdi, rsp, rbp;
@@ -141,10 +136,6 @@
/* for KVM_GET_SREGS and KVM_SET_SREGS */
struct kvm_sregs {
- /* in */
- __u32 vcpu;
- __u32 padding;
-
/* out (KVM_GET_SREGS) / in (KVM_SET_SREGS) */
struct kvm_segment cs, ds, es, fs, gs, ss;
struct kvm_segment tr, ldt;
@@ -163,8 +154,8 @@
/* for KVM_GET_MSRS and KVM_SET_MSRS */
struct kvm_msrs {
- __u32 vcpu;
__u32 nmsrs; /* number of msrs in entries */
+ __u32 pad;
struct kvm_msr_entry entries[0];
};
@@ -179,8 +170,6 @@
struct kvm_translation {
/* in */
__u64 linear_address;
- __u32 vcpu;
- __u32 padding;
/* out */
__u64 physical_address;
@@ -193,7 +182,6 @@
/* for KVM_INTERRUPT */
struct kvm_interrupt {
/* in */
- __u32 vcpu;
__u32 irq;
};
@@ -206,8 +194,8 @@
/* for KVM_DEBUG_GUEST */
struct kvm_debug_guest {
/* int */
- __u32 vcpu;
__u32 enabled;
+ __u32 pad;
struct kvm_breakpoint breakpoints[4];
__u32 singlestep;
};
@@ -234,18 +222,26 @@
/*
* ioctls for VM fds
*/
+#define KVM_SET_MEMORY_REGION _IOW(KVMIO, 10, struct kvm_memory_region)
+/*
+ * KVM_CREATE_VCPU receives as a parameter the vcpu slot, and returns
+ * a vcpu fd.
+ */
+#define KVM_CREATE_VCPU _IOW(KVMIO, 11, int)
+#define KVM_GET_DIRTY_LOG _IOW(KVMIO, 12, struct kvm_dirty_log)
+
+/*
+ * ioctls for vcpu fds
+ */
#define KVM_RUN _IOWR(KVMIO, 2, struct kvm_run)
-#define KVM_GET_REGS _IOWR(KVMIO, 3, struct kvm_regs)
+#define KVM_GET_REGS _IOR(KVMIO, 3, struct kvm_regs)
#define KVM_SET_REGS _IOW(KVMIO, 4, struct kvm_regs)
-#define KVM_GET_SREGS _IOWR(KVMIO, 5, struct kvm_sregs)
+#define KVM_GET_SREGS _IOR(KVMIO, 5, struct kvm_sregs)
#define KVM_SET_SREGS _IOW(KVMIO, 6, struct kvm_sregs)
#define KVM_TRANSLATE _IOWR(KVMIO, 7, struct kvm_translation)
#define KVM_INTERRUPT _IOW(KVMIO, 8, struct kvm_interrupt)
#define KVM_DEBUG_GUEST _IOW(KVMIO, 9, struct kvm_debug_guest)
-#define KVM_SET_MEMORY_REGION _IOW(KVMIO, 10, struct kvm_memory_region)
-#define KVM_CREATE_VCPU _IOW(KVMIO, 11, int /* vcpu_slot */)
-#define KVM_GET_DIRTY_LOG _IOW(KVMIO, 12, struct kvm_dirty_log)
#define KVM_GET_MSRS _IOWR(KVMIO, 13, struct kvm_msrs)
-#define KVM_SET_MSRS _IOWR(KVMIO, 14, struct kvm_msrs)
+#define KVM_SET_MSRS _IOW(KVMIO, 14, struct kvm_msrs)
#endif