KVM: provide synchronous registers in kvm_run

On some cpus the overhead for virtualization instructions is in the same
range as a system call. Having to call multiple ioctls to get set registers
will make certain userspace handled exits more expensive than necessary.
Lets provide a section in kvm_run that works as a shared save area
for guest registers.
We also provide two 64bit flags fields (architecture specific), that will
specify
1. which parts of these fields are valid.
2. which registers were modified by userspace

Each bit for these flag fields will define a group of registers (like
general purpose) or a single register.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index a67fb35993fa9eabde0d6ea061b6518d41f48c98..7ca696227d3a6bf915b221ea2cc5c950804d507e 100644 (file)
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1771,6 +1771,29 @@ developer registration required to access it).
                /* Fix the size of the union. */
                char padding[256];
        };
+
+       /*
+        * shared registers between kvm and userspace.
+        * kvm_valid_regs specifies the register classes set by the host
+        * kvm_dirty_regs specified the register classes dirtied by userspace
+        * struct kvm_sync_regs is architecture specific, as well as the
+        * bits for kvm_valid_regs and kvm_dirty_regs
+        */
+       __u64 kvm_valid_regs;
+       __u64 kvm_dirty_regs;
+       union {
+               struct kvm_sync_regs regs;
+               char padding[1024];
+       } s;
+
+If KVM_CAP_SYNC_REGS is defined, these fields allow userspace to access
+certain guest registers without having to call SET/GET_*REGS. Thus we can
+avoid some system call overhead if userspace has to handle the exit.
+Userspace can query the validity of the structure by checking
+kvm_valid_regs for specific bits. These bits are architecture specific
+and usually define the validity of a groups of registers. (e.g. one bit
+ for general purpose registers)
+
 };
 
 6. Capabilities that can be enabled

diff --git a/arch/ia64/include/asm/kvm.h b/arch/ia64/include/asm/kvm.h
index bc90c75adf6716f8423fe92935fa9fbd7be89cf2..b9f82c84f0932cff844ca97d09c3a6291c92e908 100644 (file)
--- a/arch/ia64/include/asm/kvm.h
+++ b/arch/ia64/include/asm/kvm.h
@@ -261,4 +261,8 @@ struct kvm_debug_exit_arch {
 struct kvm_guest_debug_arch {
 };
 
+/* definition of registers in kvm_run */
+struct kvm_sync_regs {
+};
+
 #endif

diff --git a/arch/powerpc/include/asm/kvm.h b/arch/powerpc/include/asm/kvm.h
index f7727d91ac6b91d26325fdbbae46cc9e7698cba2..7d9d4de057ef36e80ef08ebfc6a6403ec27c2e21 100644 (file)
--- a/arch/powerpc/include/asm/kvm.h
+++ b/arch/powerpc/include/asm/kvm.h
@@ -265,6 +265,10 @@ struct kvm_debug_exit_arch {
 struct kvm_guest_debug_arch {
 };
 
+/* definition of registers in kvm_run */
+struct kvm_sync_regs {
+};
+
 #define KVM_REG_MASK           0x001f
 #define KVM_REG_EXT_MASK       0xffe0
 #define KVM_REG_GPR            0x0000

diff --git a/arch/s390/include/asm/kvm.h b/arch/s390/include/asm/kvm.h
index 82b32a100c7ddc18f69547ca40ec946e873852c6..325560afb77e838b1c5bfd4bfaefd59688b5f28c 100644 (file)
--- a/arch/s390/include/asm/kvm.h
+++ b/arch/s390/include/asm/kvm.h
@@ -41,4 +41,7 @@ struct kvm_debug_exit_arch {
 struct kvm_guest_debug_arch {
 };
 
+/* definition of registers in kvm_run */
+struct kvm_sync_regs {
+};
 #endif

diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
index 4d8dcbdfc1205956c3b90b6f13d6bff021b63860..e7d1c194d27280381ae302f9d1aac2d69a872b2e 100644 (file)
--- a/arch/x86/include/asm/kvm.h
+++ b/arch/x86/include/asm/kvm.h
@@ -321,4 +321,8 @@ struct kvm_xcrs {
        __u64 padding[16];
 };
 
+/* definition of registers in kvm_run */
+struct kvm_sync_regs {
+};
+
 #endif /* _ASM_X86_KVM_H */

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 6cf048d9604bef8a03e637984b0ef25af090383c..245bcb3a0fcd08305fdfb0c6ace86c627adf116b 100644 (file)
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -279,6 +279,20 @@ struct kvm_run {
                /* Fix the size of the union. */
                char padding[256];
        };
+
+       /*
+        * shared registers between kvm and userspace.
+        * kvm_valid_regs specifies the register classes set by the host
+        * kvm_dirty_regs specified the register classes dirtied by userspace
+        * struct kvm_sync_regs is architecture specific, as well as the
+        * bits for kvm_valid_regs and kvm_dirty_regs
+        */
+       __u64 kvm_valid_regs;
+       __u64 kvm_dirty_regs;
+       union {
+               struct kvm_sync_regs regs;
+               char padding[1024];
+       } s;
 };
 
 /* for KVM_REGISTER_COALESCED_MMIO / KVM_UNREGISTER_COALESCED_MMIO */
@@ -570,6 +584,7 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_S390_GMAP 71
 #define KVM_CAP_TSC_DEADLINE_TIMER 72
 #define KVM_CAP_S390_UCONTROL 73
+#define KVM_CAP_SYNC_REGS 74
 
 #ifdef KVM_CAP_IRQ_ROUTING