[PATCH 5/5] kvm/svm: copy instruction bytes from VMCB

[Andre Przywara <andre.przywara@amd.com>]

In case of a nested page fault or an intercepted #PF newer SVM
implementations provide a copy of the faulting instruction bytes
in the VMCB.
Use these bytes to feed the instruction emulator and avoid the costly
guest instruction fetch in this case.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>
---
 arch/x86/include/asm/kvm_host.h |    3 +++
 arch/x86/include/asm/svm.h      |    4 +++-
 arch/x86/kvm/emulate.c          |    1 +
 arch/x86/kvm/svm.c              |   20 ++++++++++++++++++++
 arch/x86/kvm/vmx.c              |    7 +++++++
 5 files changed, 34 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 2b89195..baaf063 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -586,6 +586,9 @@ struct kvm_x86_ops {
 	void (*write_tsc_offset)(struct kvm_vcpu *vcpu, u64 offset);
 
 	void (*get_exit_info)(struct kvm_vcpu *vcpu, u64 *info1, u64 *info2);
+
+	int (*prefetch_instruction)(struct kvm_vcpu *vcpu);
+
 	const struct trace_print_flags *exit_reasons_str;
 };
 
diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 589fc25..6d64b1d 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -81,7 +81,9 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
 	u64 lbr_ctl;
 	u64 reserved_5;
 	u64 next_rip;
-	u8 reserved_6[816];
+	u8 insn_len;
+	u8 insn_bytes[15];
+	u8 reserved_6[800];
 };
 
 
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6366735..70385ee 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2623,6 +2623,7 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt)
 	c->eip = ctxt->eip;
 	c->fetch.start = c->fetch.end = c->eip;
 	ctxt->cs_base = seg_base(ctxt, ops, VCPU_SREG_CS);
+	kvm_x86_ops->prefetch_instruction(ctxt->vcpu);
 
 	switch (mode) {
 	case X86EMUL_MODE_REAL:
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 73f1a6d..685b264 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -464,6 +464,24 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 	svm_set_interrupt_shadow(vcpu, 0);
 }
 
+static int svm_prefetch_instruction(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+	uint8_t len;
+	struct fetch_cache *fetch;
+
+	len = svm->vmcb->control.insn_len & 0x0F;
+	if (len == 0)
+		return 1;
+
+	fetch = &svm->vcpu.arch.emulate_ctxt.decode.fetch;
+	fetch->start = kvm_rip_read(&svm->vcpu);
+	fetch->end = fetch->start + len;
+	memcpy(fetch->data, svm->vmcb->control.insn_bytes, len);
+
+	return 0;
+}
+
 static void svm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
 				bool has_error_code, u32 error_code,
 				bool reinject)
@@ -3848,6 +3866,8 @@ static struct kvm_x86_ops svm_x86_ops = {
 	.adjust_tsc_offset = svm_adjust_tsc_offset,
 
 	.set_tdp_cr3 = set_tdp_cr3,
+
+	.prefetch_instruction = svm_prefetch_instruction,
 };
 
 static int __init svm_init(void)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index e5ef924..7572751 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1009,6 +1009,11 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 	vmx_set_interrupt_shadow(vcpu, 0);
 }
 
+static int vmx_prefetch_instruction(struct kvm_vcpu *vcpu)
+{
+	return 1;
+}
+
 static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
 				bool has_error_code, u32 error_code,
 				bool reinject)
@@ -4362,6 +4367,8 @@ static struct kvm_x86_ops vmx_x86_ops = {
 	.adjust_tsc_offset = vmx_adjust_tsc_offset,
 
 	.set_tdp_cr3 = vmx_set_cr3,
+
+	.prefetch_instruction = vmx_prefetch_instruction,
 };
 
 static int __init vmx_init(void)
-- 
1.6.4