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

Andre Przywara
2010-12-07T11:09:51Z

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 cfbcbfa..3e3a67e 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..abff8ff 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -525,6 +525,7 @@ static int do_insn_fetch(struct x86_emulate_ctxt *ctxt,
/* x86 instructions are limited to 15 bytes. */
if (eip + size - ctxt->eip > 15)
return X86EMUL_UNHANDLEABLE;
+ kvm_x86_ops->prefetch_instruction(ctxt->vcpu);
while (size--) {
rc = do_fetch_insn_byte(ctxt, ops, eip++, dest++);
if (rc != X86EMUL_CONTINUE)
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 3cf2cef..ed94e9a 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 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)
@@ -3830,6 +3848,8 @@ static struct kvm_x86_ops svm_x86_ops = {
.adjust_tsc_offset = svm_adjust_tsc_offset,

.set_tdp_cr3 = set_tdp_cr3,
+
+ .prefetch_instruction = prefetch_instruction,
};

static int __init svm_init(void)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 72cfdb7..4825545 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 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 = prefetch_instruction,
};

static int __init vmx_init(void)
--
1.6.4