Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933673AbaFINAF (ORCPT ); Mon, 9 Jun 2014 09:00:05 -0400 Received: from mail-we0-f179.google.com ([74.125.82.179]:46063 "EHLO mail-we0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933546AbaFIM7v (ORCPT ); Mon, 9 Jun 2014 08:59:51 -0400 From: Paolo Bonzini To: linux-kernel@vger.kernel.org Cc: bdas@redhat.com, gleb@kernel.org Subject: [PATCH 20/25] KVM: emulate: avoid repeated calls to do_insn_fetch_bytes Date: Mon, 9 Jun 2014 14:59:08 +0200 Message-Id: <1402318753-23362-21-git-send-email-pbonzini@redhat.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1402318753-23362-1-git-send-email-pbonzini@redhat.com> References: <1402318753-23362-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org do_insn_fetch_bytes will only be called once in a given insn_fetch and insn_fetch_arr, because in fact it will only be called at most twice for any instruction and the first call is explicit in x86_decode_insn. This observation lets us hoist the call out of the memory copying loop. It does not buy performance, because most fetches are one byte long anyway, but it prepares for the next patch. The overflow check is tricky, but correct. Because do_insn_fetch_bytes has already been called once, we know that fc->end is at least 15. So it is okay to subtract the number of bytes we want to read. Signed-off-by: Paolo Bonzini --- arch/x86/kvm/emulate.c | 26 +++++++++++++++++--------- 1 file changed, 17 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index aee124a4cc6c..f81d7a5bc19b 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -707,7 +707,7 @@ 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) +static int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size) { struct fetch_cache *fc = &ctxt->fetch; int rc; @@ -719,7 +719,14 @@ static int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt) cur_size = fc->end - fc->start; size = min(15UL - cur_size, PAGE_SIZE - offset_in_page(fc->end)); - if (unlikely(size == 0)) + + /* + * One instruction can only straddle two pages, + * and one has been loaded at the beginning of + * x86_decode_insn. So, if not enough bytes + * still, we must have hit the 15-byte boundary. + */ + if (unlikely(size < op_size)) return X86EMUL_UNHANDLEABLE; rc = __linearize(ctxt, addr, size, false, true, &linear); if (unlikely(rc != X86EMUL_CONTINUE)) @@ -735,17 +742,18 @@ static int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt) static int do_insn_fetch(struct x86_emulate_ctxt *ctxt, void *__dest, 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)) { + int rc = do_insn_fetch_bytes(ctxt, size); + if (rc != X86EMUL_CONTINUE) + return rc; + } + while (size--) { - if (unlikely(ctxt->_eip == fc->end)) { - rc = do_insn_fetch_bytes(ctxt); - if (rc != X86EMUL_CONTINUE) - return rc; - } *dest++ = *src++; ctxt->_eip++; continue; @@ -4302,7 +4310,7 @@ 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); + rc = do_insn_fetch_bytes(ctxt, 1); if (rc != X86EMUL_CONTINUE) return rc; } -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/