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Commit 9506d57d authored by Paolo Bonzini's avatar Paolo Bonzini
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KVM: emulate: avoid per-byte copying in instruction fetches 



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 50-150 cycles (corresponding to
a 5-10% improvement in performance) from each instruction.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 5cfc7e0f

arch/x86/kvm/emulate.c

+22 −24
Original line number Diff line number Diff line
@@ -708,7 +708,7 @@ 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;
@@ -740,41 +740,39 @@ 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)

{

	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)) {

		int rc = do_insn_fetch_bytes(ctxt, size);

		if (rc != X86EMUL_CONTINUE)

			return rc;

	}



	while (size--) {

		*dest++ = *src++;

		ctxt->_eip++;

		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);						\

})



/*
@@ -4236,7 +4234,7 @@ 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;

	}