[patch 1/3] kvm: provide synchronous registers in kvm_run

[Christian Borntraeger <borntraeger@de.ibm.com>]

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From: Christian Borntraeger <borntraeger@de.ibm.com>

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 userspace handled exits more expensive than necessary.
Lets provide two sections in kvm_run to have a shared save area for
guest registers.
1. the first section is read-only, to handle registers that have side-effects
2. the second section is read/write, e.g. for general purpose registers.


Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 Documentation/virtual/kvm/api.txt |   16 ++++++++++++++++
 arch/ia64/include/asm/kvm.h       |    7 +++++++
 arch/powerpc/include/asm/kvm.h    |    7 +++++++
 arch/s390/include/asm/kvm.h       |    6 ++++++
 arch/x86/include/asm/kvm.h        |    7 +++++++
 include/linux/kvm.h               |   13 +++++++++++++
 6 files changed, 56 insertions(+)

Index: b/Documentation/virtual/kvm/api.txt
===================================================================
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1652,7 +1652,23 @@ developer registration required to acces
 		/* Fix the size of the union. */
 		char padding[256];
 	};
+	/* Here are two fields that allow to access often used registers
+         * directly, to avoid the overhead of the ioctl system call */
+	union {
+		/* registers which can be only read */
+		struct sync_ro_regs sync_ro_regs;
+		char padding[1024];
+	};
+	union {
+		/* read/write guest registers */
+		struct sync_rw_regs sync_rw_regs;
+		char padding[1024];
+	};
 };
+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. (only available if
+KVM_CAP_SYNC_REGS is set). The ioctls will still work.
 
 6. Capabilities that can be enabled
 
Index: b/arch/ia64/include/asm/kvm.h
===================================================================
--- a/arch/ia64/include/asm/kvm.h
+++ b/arch/ia64/include/asm/kvm.h
@@ -261,4 +261,11 @@ struct kvm_debug_exit_arch {
 struct kvm_guest_debug_arch {
 };
 
+/* definition of registers in kvm_run */
+struct sync_ro_regs {
+};
+
+struct sync_rw_regs {
+};
+
 #endif
Index: b/arch/powerpc/include/asm/kvm.h
===================================================================
--- a/arch/powerpc/include/asm/kvm.h
+++ b/arch/powerpc/include/asm/kvm.h
@@ -265,6 +265,13 @@ struct kvm_debug_exit_arch {
 struct kvm_guest_debug_arch {
 };
 
+/* definition of registers in kvm_run */
+struct sync_ro_regs {
+};
+
+struct sync_rw_regs {
+};
+
 #define KVM_REG_MASK		0x001f
 #define KVM_REG_EXT_MASK	0xffe0
 #define KVM_REG_GPR		0x0000
Index: b/arch/s390/include/asm/kvm.h
===================================================================
--- a/arch/s390/include/asm/kvm.h
+++ b/arch/s390/include/asm/kvm.h
@@ -41,4 +41,10 @@ struct kvm_debug_exit_arch {
 struct kvm_guest_debug_arch {
 };
 
+/* definition of registers in kvm_run */
+struct sync_ro_regs {
+};
+
+struct sync_rw_regs {
+};
 #endif
Index: b/arch/x86/include/asm/kvm.h
===================================================================
--- a/arch/x86/include/asm/kvm.h
+++ b/arch/x86/include/asm/kvm.h
@@ -321,4 +321,11 @@ struct kvm_xcrs {
 	__u64 padding[16];
 };
 
+/* definition of registers in kvm_run */
+struct sync_ro_regs {
+};
+
+struct sync_rw_regs {
+};
+
 #endif /* _ASM_X86_KVM_H */
Index: b/include/linux/kvm.h
===================================================================
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -273,6 +273,18 @@ struct kvm_run {
 		/* Fix the size of the union. */
 		char padding[256];
 	};
+	/* Here are two fields that allow to access often used registers
+         * directly, to avoid the overhead of the ioctl system call */
+	union {
+		/* registers which can be only read */
+		struct sync_ro_regs sync_ro_regs;
+		char padding[1024];
+	};
+	union {
+		/* read/write guest registers */
+		struct sync_rw_regs sync_rw_regs;
+		char padding[1024];
+	};
 };
 
 /* for KVM_REGISTER_COALESCED_MMIO / KVM_UNREGISTER_COALESCED_MMIO */
@@ -557,6 +569,7 @@ struct kvm_ppc_pvinfo {
 #define KVM_CAP_MAX_VCPUS 66       /* returns max vcpus per vm */
 #define KVM_CAP_PPC_PAPR 68
 #define KVM_CAP_S390_GMAP 71
+#define KVM_CAP_SYNC_REGS 72
 
 #ifdef KVM_CAP_IRQ_ROUTING