From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Desaulniers Subject: [PATCH v3] KVM: x86: avoid large stack allocations in em_fxrstor Date: Mon, 29 May 2017 13:39:08 -0700 Message-ID: <20170529203908.10775-1-nick.desaulniers@gmail.com> References: <20170529195538.27419-1-nick.desaulniers@gmail.com> Cc: Nick Desaulniers , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: unlisted-recipients:; (no To-header on input) Return-path: Received: from mail-pf0-f193.google.com ([209.85.192.193]:34259 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751061AbdE2UjU (ORCPT ); Mon, 29 May 2017 16:39:20 -0400 In-Reply-To: <20170529195538.27419-1-nick.desaulniers@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: em_fxstor previously called fxstor_fixup. Both created instances of struct fxregs_state on the stack, which triggered the warning: arch/x86/kvm/emulate.c:4018:12: warning: stack frame size of 1080 bytes in function 'em_fxrstor' [-Wframe-larger-than=] static int em_fxrstor(struct x86_emulate_ctxt *ctxt) ^ with CONFIG_FRAME_WARN set to 1024. This patch does the fixup in em_fxstor now, avoiding one additional struct fxregs_state, and now fxstor_fixup can be removed as it has no other call sites. Signed-off-by: Nick Desaulniers --- New in V3: * initialized size to 0 to avoid maybe-uninitialized warning. Check that it gets set to something other than 0 before passing size to segmented_read_std(). New in V2: * reworked patch to do what was recommended by maintainers in: https://lkml.org/lkml/2017/5/25/391 arch/x86/kvm/emulate.c | 58 +++++++++++++++++++------------------------------- 1 file changed, 22 insertions(+), 36 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 0816ab2e8adc..8c74a3764405 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -3985,57 +3985,43 @@ static int em_fxsave(struct x86_emulate_ctxt *ctxt) return segmented_write_std(ctxt, ctxt->memop.addr.mem, &fx_state, size); } -static int fxrstor_fixup(struct x86_emulate_ctxt *ctxt, - struct fxregs_state *new) -{ - int rc = X86EMUL_CONTINUE; - struct fxregs_state old; - - rc = asm_safe("fxsave %[fx]", , [fx] "+m"(old)); - if (rc != X86EMUL_CONTINUE) - return rc; - - /* - * 64 bit host will restore XMM 8-15, which is not correct on non-64 - * bit guests. Load the current values in order to preserve 64 bit - * XMMs after fxrstor. - */ -#ifdef CONFIG_X86_64 - /* XXX: accessing XMM 8-15 very awkwardly */ - memcpy(&new->xmm_space[8 * 16/4], &old.xmm_space[8 * 16/4], 8 * 16); -#endif - - /* - * Hardware doesn't save and restore XMM 0-7 without CR4.OSFXSR, but - * does save and restore MXCSR. - */ - if (!(ctxt->ops->get_cr(ctxt, 4) & X86_CR4_OSFXSR)) - memcpy(new->xmm_space, old.xmm_space, 8 * 16); - - return rc; -} - static int em_fxrstor(struct x86_emulate_ctxt *ctxt) { struct fxregs_state fx_state; int rc; + unsigned int size = 0; rc = check_fxsr(ctxt); if (rc != X86EMUL_CONTINUE) return rc; - rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state, 512); + ctxt->ops->get_fpu(ctxt); + + if (ctxt->mode < X86EMUL_MODE_PROT64) { + rc = asm_safe("fxsave %[fx]", , [fx] "+m"(fx_state)); + if (rc != X86EMUL_CONTINUE) + return rc; + /* + * Hardware doesn't save and restore XMM 0-7 without + * CR4.OSFXSR, but does save and restore MXCSR. + */ + if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_OSFXSR) + size = offsetof(struct fxregs_state, xmm_space[8]); + else + size = offsetof(struct fxregs_state, xmm_space[0]); + } else if (ctxt->mode == X86EMUL_MODE_PROT64) + size = offsetof(struct fxregs_state, xmm_space[16]); + + if (size == 0) + return X86EMUL_UNHANDLEABLE; + + rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state, size); if (rc != X86EMUL_CONTINUE) return rc; if (fx_state.mxcsr >> 16) return emulate_gp(ctxt, 0); - ctxt->ops->get_fpu(ctxt); - - if (ctxt->mode < X86EMUL_MODE_PROT64) - rc = fxrstor_fixup(ctxt, &fx_state); - if (rc == X86EMUL_CONTINUE) rc = asm_safe("fxrstor %[fx]", : [fx] "m"(fx_state)); -- 2.11.0