We do not need a memory copying loop anymore in insn_fetch; we
can use a byte-aligned pointer to access instruction fields directly
from the fetch_cache. This eliminates 40-80 cycles (corresponding to
a 5-7% improvement in performance) from each instruction.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/emulate.c | 47 ++++++++++++++++++++++-------------------------
1 file changed, 22 insertions(+), 25 deletions(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 886f9a88010f..245a2d0bfe68 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -706,7 +706,7 @@ static int segmented_read_std(struct x86_emulate_ctxt *ctxt,
* Prefetch the remaining bytes of the instruction without crossing page
* boundary if they are not in fetch_cache yet.
*/
-static int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
+static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
{
struct fetch_cache *fc = &ctxt->fetch;
int rc;
@@ -738,42 +738,39 @@ static int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
return X86EMUL_CONTINUE;
}
-static int do_insn_fetch(struct x86_emulate_ctxt *ctxt,
- void *__dest, unsigned size)
+static __always_inline int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt,
+ unsigned size)
{
- int rc;
- struct fetch_cache *fc = &ctxt->fetch;
- u8 *dest = __dest;
- u8 *src = &fc->data[ctxt->_eip - fc->start];
-
/* We have to be careful about overflow! */
- if (unlikely(ctxt->_eip > fc->end - size)) {
- rc != do_insn_fetch_bytes(ctxt, size);
- if (rc != X86EMUL_CONTINNUE)
- goto done;
- }
-
- while (size--) {
- *dest++ = *src++;
- ctxt->_eip++;
- continue;
- }
- return X86EMUL_CONTINUE;
+ if (unlikely(ctxt->_eip > ctxt->fetch.end - size))
+ return __do_insn_fetch_bytes(ctxt, size);
+ else
+ return X86EMUL_CONTINUE;
}
/* Fetch next part of the instruction being emulated. */
#define insn_fetch(_type, _ctxt) \
-({ unsigned long _x; \
- rc = do_insn_fetch(_ctxt, &_x, sizeof(_type)); \
+({ _type _x; \
+ struct fetch_cache *_fc; \
+ \
+ rc = do_insn_fetch_bytes(_ctxt, sizeof(_type)); \
if (rc != X86EMUL_CONTINUE) \
goto done; \
- (_type)_x; \
+ _fc = &ctxt->fetch; \
+ _x = *(_type __aligned(1) *) &_fc->data[ctxt->_eip - _fc->start]; \
+ ctxt->_eip += sizeof(_type); \
+ _x; \
})
#define insn_fetch_arr(_arr, _size, _ctxt) \
-({ rc = do_insn_fetch(_ctxt, _arr, (_size)); \
+({ \
+ struct fetch_cache *_fc; \
+ rc = do_insn_fetch_bytes(_ctxt, _size); \
if (rc != X86EMUL_CONTINUE) \
goto done; \
+ _fc = &ctxt->fetch; \
+ memcpy(_arr, &_fc->data[ctxt->_eip - _fc->start], _size); \
+ ctxt->_eip += (_size); \
})
/*
@@ -4282,7 +4279,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
if (insn_len > 0)
memcpy(ctxt->fetch.data, insn, insn_len);
else {
- rc = do_insn_fetch_bytes(ctxt, 1);
+ rc = __do_insn_fetch_bytes(ctxt, 1);
if (rc != X86EMUL_CONTINUE)
return rc;
}
--
1.8.3.1
--
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