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Commit 285ca9e9 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: emulate: speed up do_insn_fetch 



Hoist the common case up from do_insn_fetch_byte to do_insn_fetch,
and prime the fetch_cache in x86_decode_insn.  This helps a bit the
compiler and the branch predictor, but above all it lays the
ground for further changes in the next few patches.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 41061cdb

arch/x86/kvm/emulate.c

+36 −31
Original line number Diff line number Diff line
@@ -705,25 +705,23 @@ static int segmented_read_std(struct x86_emulate_ctxt *ctxt, 
}



/*

 * Fetch the next byte of the instruction being emulated which is pointed to

 * by ctxt->_eip, then increment ctxt->_eip.

 *

 * Also prefetch the remaining bytes of the instruction without crossing page

 * Prefetch the remaining bytes of the instruction without crossing page

 * boundary if they are not in fetch_cache yet.

 */

static int do_insn_fetch_byte(struct x86_emulate_ctxt *ctxt, u8 *dest)

static int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt)

{

	struct fetch_cache *fc = &ctxt->fetch;

	int rc;

	int size, cur_size;



	if (ctxt->_eip == fc->end) {

	unsigned long linear;



	struct segmented_address addr = { .seg = VCPU_SREG_CS,

						  .ea  = ctxt->_eip };

					  .ea  = fc->end };

	cur_size = fc->end - fc->start;

	size = min(15UL - cur_size,

			   PAGE_SIZE - offset_in_page(ctxt->_eip));

		   PAGE_SIZE - offset_in_page(fc->end));

	if (unlikely(size == 0))

		return X86EMUL_UNHANDLEABLE;

	rc = __linearize(ctxt, addr, size, false, true, &linear);

	if (unlikely(rc != X86EMUL_CONTINUE))

		return rc;
@@ -732,25 +730,27 @@ static int do_insn_fetch_byte(struct x86_emulate_ctxt *ctxt, u8 *dest) 
	if (unlikely(rc != X86EMUL_CONTINUE))

		return rc;

	fc->end += size;

	}

	*dest = fc->data[ctxt->_eip - fc->start];

	ctxt->_eip++;

	return X86EMUL_CONTINUE;

}



static int do_insn_fetch(struct x86_emulate_ctxt *ctxt,

			 void *dest, unsigned size)

			 void *__dest, unsigned size)

{

	int rc;

	struct fetch_cache *fc = &ctxt->fetch;

	u8 *dest = __dest;

	u8 *src = &fc->data[ctxt->_eip - fc->start];



	/* x86 instructions are limited to 15 bytes. */

	if (unlikely(ctxt->_eip + size - ctxt->eip > 15))

		return X86EMUL_UNHANDLEABLE;

	while (size--) {

		rc = do_insn_fetch_byte(ctxt, dest++);

		if (unlikely(ctxt->_eip == fc->end)) {

			rc = do_insn_fetch_bytes(ctxt);

			if (rc != X86EMUL_CONTINUE)

				return rc;

		}

		*dest++ = *src++;

		ctxt->_eip++;

		continue;

	}

	return X86EMUL_CONTINUE;

}
@@ -4227,6 +4227,11 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len) 
	ctxt->opcode_len = 1;

	if (insn_len > 0)

		memcpy(ctxt->fetch.data, insn, insn_len);

	else {

		rc = do_insn_fetch_bytes(ctxt);

		if (rc != X86EMUL_CONTINUE)

			return rc;

	}



	switch (mode) {

	case X86EMUL_MODE_REAL: