From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2C20DC433E2 for ; Tue, 15 Sep 2020 02:42:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 02B8320897 for ; Tue, 15 Sep 2020 02:42:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726118AbgIOCmE (ORCPT ); Mon, 14 Sep 2020 22:42:04 -0400 Received: from mga02.intel.com ([134.134.136.20]:58954 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726035AbgIOCmC (ORCPT ); Mon, 14 Sep 2020 22:42:02 -0400 IronPort-SDR: AB/2b5g1mhnqbDWad7WIFULemAnflptnRXCzhImn/kBPFYa1zl5ZEB5Sj9gvdHUgZrRmVp2sG9 GRj0JqTciCoA== X-IronPort-AV: E=McAfee;i="6000,8403,9744"; a="146879518" X-IronPort-AV: E=Sophos;i="5.76,428,1592895600"; d="scan'208";a="146879518" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Sep 2020 19:42:02 -0700 IronPort-SDR: BmrQGyB+8l574LwXi+Sq9NLBI0yRDeieQgipDhcbe6Xk0rr16sfhjEsOw1tzOMjx/ct/hoZSqz h14tUu38B/9Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.76,428,1592895600"; d="scan'208";a="343330939" Received: from tassilo.jf.intel.com (HELO tassilo.localdomain) ([10.54.74.11]) by FMSMGA003.fm.intel.com with ESMTP; 14 Sep 2020 19:42:01 -0700 Received: by tassilo.localdomain (Postfix, from userid 1000) id B4C26301C59; Mon, 14 Sep 2020 19:42:01 -0700 (PDT) Date: Mon, 14 Sep 2020 19:42:01 -0700 From: Andi Kleen To: Sean Christopherson Cc: Josh Poimboeuf , Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Uros Bizjak Subject: Re: [PATCH 1/2] KVM: VMX: Move IRQ invocation to assembly subroutine Message-ID: <20200915024201.GA13818@tassilo.jf.intel.com> References: <20200914195634.12881-1-sean.j.christopherson@intel.com> <20200914195634.12881-2-sean.j.christopherson@intel.com> <20200914204024.w3rpjon64d3fesys@treble> <20200914210719.GB7084@sjchrist-ice> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200914210719.GB7084@sjchrist-ice> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, Sep 14, 2020 at 02:07:19PM -0700, Sean Christopherson wrote: > 16-byte aligned to correctly mimic CPU behavior when vectoring an IRQ/NMI. > When not changing stack, the CPU aligns RSP before pushing the frame. 16 byte alignment is not needed for the internal kernel ABI because it doesn't use SSE. -Andi > > The above shenanigans work because the x86-64 ABI also requires RSP to be > 16-byte aligned prior to CALL. RSP is thus 8-byte aligned due to CALL > pushing the return IP, and so creating the stack frame by pushing RBP makes > it 16-byte aliagned again. > > > > + > > > +#ifdef CONFIG_X86_64 > > > + push $__KERNEL_DS > > > + push %_ASM_BP > > > +#endif > > > + pushf > > > + push $__KERNEL_CS > > > + CALL_NOSPEC _ASM_ARG1 > > > + > > > + /* > > > + * "Restore" RSP from RBP, even though IRET has already unwound RSP to > > > + * the correct value. objtool doesn't know the target will IRET and so > > > + * thinks the stack is getting walloped (without the explicit restore). > > > + */ > > > + mov %_ASM_BP, %rsp > > > + pop %_ASM_BP > > > + ret > > > > BTW, there *is* actually an unwind hint for this situation: > > UNWIND_HINT_RET_OFFSET. > > I played with that one, but for the life of me couldn't figure out how to > satisfy both the "stack size" and "cfa.offset" checks. In the code below, > cfa.offset will be 8, stack_size will be 40 and initial_func_cfi.cfa.offset > will be 8. But rereading this, I assume I missed something that would allow > maniuplating cfa.offset? Or maybe I botched my debugging? > > static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state) > { > ... > > if (cfi->cfa.offset != initial_func_cfi.cfa.offset + ret_offset) > return true; > > if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset) > return true; > > ... > } > > > So you might be able to do something like the following (depending on > > what your alignment requirements actually are): > > > > SYM_FUNC_START(vmx_do_interrupt_nmi_irqoff) > > #ifdef CONFIG_X86_64 > > push $__KERNEL_DS > > push %_ASM_BP > > #endif > > pushf > > push $__KERNEL_CS > > CALL_NOSPEC _ASM_ARG1 > > > > /* The call popped the pushes */ > > UNWIND_HINT_RET_OFFSET sp_offset=32 > > > > ret > > SYM_FUNC_END(vmx_do_interrupt_nmi_irqoff) > > > > -- > > Josh > >