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Subject[PATCH 2/6] kvm, emulator: Use opcode length
Date
From: Borislav Petkov <bp@suse.de>

Add a field to the current emulation context which contains the
instruction opcode length. This will streamline handling of opcodes of
different length.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/include/asm/kvm_emulate.h | 8 ++++++--
arch/x86/kvm/emulate.c | 5 +++--
arch/x86/kvm/x86.c | 4 ++--
3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 15f960c06ff7..92a176ad456c 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -279,8 +279,12 @@ struct x86_emulate_ctxt {
bool have_exception;
struct x86_exception exception;

- /* decode cache */
- u8 twobyte;
+ /*
+ * decode cache
+ */
+
+ /* current opcode length in bytes */
+ u8 opcode_len;
u8 b;
u8 intercept;
u8 lock_prefix;
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 2bc1e81045b0..bfae4a433091 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4114,6 +4114,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
ctxt->_eip = ctxt->eip;
ctxt->fetch.start = ctxt->_eip;
ctxt->fetch.end = ctxt->fetch.start + insn_len;
+ ctxt->opcode_len = 1;
if (insn_len > 0)
memcpy(ctxt->fetch.data, insn, insn_len);

@@ -4196,7 +4197,7 @@ done_prefixes:
opcode = opcode_table[ctxt->b];
/* Two-byte opcode? */
if (ctxt->b == 0x0f) {
- ctxt->twobyte = 1;
+ ctxt->opcode_len = 2;
ctxt->b = insn_fetch(u8, ctxt);
opcode = twobyte_table[ctxt->b];
}
@@ -4528,7 +4529,7 @@ special_insn:
goto writeback;
}

- if (ctxt->twobyte)
+ if (ctxt->opcode_len == 2)
goto twobyte_insn;

switch (ctxt->b) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8dfde7a52dab..6f2ea40b80cf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4778,8 +4778,8 @@ static void inject_emulated_exception(struct kvm_vcpu *vcpu)

static void init_decode_cache(struct x86_emulate_ctxt *ctxt)
{
- memset(&ctxt->twobyte, 0,
- (void *)&ctxt->_regs - (void *)&ctxt->twobyte);
+ memset(&ctxt->opcode_len, 0,
+ (void *)&ctxt->_regs - (void *)&ctxt->opcode_len);

ctxt->fetch.start = 0;
ctxt->fetch.end = 0;
--
1.8.4


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