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=-11.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 E1C9BC4727C for ; Mon, 28 Sep 2020 03:41:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AD4F1239A1 for ; Mon, 28 Sep 2020 03:41:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726526AbgI1Dix (ORCPT ); Sun, 27 Sep 2020 23:38:53 -0400 Received: from mga09.intel.com ([134.134.136.24]:2207 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbgI1Diw (ORCPT ); Sun, 27 Sep 2020 23:38:52 -0400 IronPort-SDR: CwQdDTtLZMSCIC5pEv7rHed8Hm4QCvYq3g8DMYEw6p7kWPNfYJZLX1zdNtdVi6Jo4XVgvAzLZ2 +FSQqa105loA== X-IronPort-AV: E=McAfee;i="6000,8403,9757"; a="162821908" X-IronPort-AV: E=Sophos;i="5.77,312,1596524400"; d="scan'208";a="162821908" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Sep 2020 20:38:52 -0700 IronPort-SDR: NV693pBxXF8iAtTv683mtj4ZikTsIhoz1VcR8ga4XDN4ByAE5UIb7frihh+hBsAUEWuF1l7gCU xYGFXnpIIerg== X-IronPort-AV: E=Sophos;i="5.77,312,1596524400"; d="scan'208";a="488392698" Received: from shuo-intel.sh.intel.com (HELO localhost) ([10.239.154.30]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Sep 2020 20:38:48 -0700 Date: Mon, 28 Sep 2020 11:38:46 +0800 From: Shuo A Liu To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, x86@kernel.org, "H . Peter Anvin" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Sean Christopherson , Yu Wang , Reinette Chatre , Yakui Zhao , Dave Hansen , Dan Williams , Fengwei Yin , Zhi Wang , Zhenyu Wang Subject: Re: [PATCH v4 04/17] x86/acrn: Introduce hypercall interfaces Message-ID: <20200928033846.GB1057@shuo-intel.sh.intel.com> References: <20200922114311.38804-1-shuo.a.liu@intel.com> <20200922114311.38804-5-shuo.a.liu@intel.com> <20200927105152.GG88650@kroah.com> <20200927105314.GH88650@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20200927105314.GH88650@kroah.com> User-Agent: Mutt/1.8.3 (2017-05-23) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun 27.Sep'20 at 12:53:14 +0200, Greg Kroah-Hartman wrote: >On Sun, Sep 27, 2020 at 12:51:52PM +0200, Greg Kroah-Hartman wrote: >> On Tue, Sep 22, 2020 at 07:42:58PM +0800, shuo.a.liu@intel.com wrote: >> > From: Shuo Liu >> > >> > The Service VM communicates with the hypervisor via conventional >> > hypercalls. VMCALL instruction is used to make the hypercalls. >> > >> > ACRN hypercall ABI: >> > * Hypercall number is in R8 register. >> > * Up to 2 parameters are in RDI and RSI registers. >> > * Return value is in RAX register. >> > >> > Introduce the ACRN hypercall interfaces. Because GCC doesn't support R8 >> > register as direct register constraints, here are two ways to use R8 in >> > extended asm: >> > 1) use explicit register variable as input >> > 2) use supported constraint as input with a explicit MOV to R8 in >> > beginning of asm >> > >> > The number of instructions of above two ways are same. >> > Asm code from 1) >> > 38: 41 b8 00 00 00 80 mov $0x80000000,%r8d >> > 3e: 48 89 c7 mov %rax,%rdi >> > 41: 0f 01 c1 vmcall >> > Here, writes to the lower dword (%r8d) clear the upper dword of %r8 when >> > the CPU is in 64-bit mode. >> > >> > Asm code from 2) >> > 38: 48 89 c7 mov %rax,%rdi >> > 3b: 49 b8 00 00 00 80 00 movabs $0x80000000,%r8 >> > 42: 00 00 00 >> > 45: 0f 01 c1 vmcall >> > >> > Choose 1) for code simplicity and a little bit of code size >> > optimization. >> > >> > Originally-by: Yakui Zhao >> > Signed-off-by: Shuo Liu >> > Reviewed-by: Reinette Chatre >> > Cc: Dave Hansen >> > Cc: Sean Christopherson >> > Cc: Dan Williams >> > Cc: Fengwei Yin >> > Cc: Zhi Wang >> > Cc: Zhenyu Wang >> > Cc: Yu Wang >> > Cc: Reinette Chatre >> > Cc: Greg Kroah-Hartman >> > --- >> > arch/x86/include/asm/acrn.h | 57 +++++++++++++++++++++++++++++++++++++ >> > 1 file changed, 57 insertions(+) >> > >> > diff --git a/arch/x86/include/asm/acrn.h b/arch/x86/include/asm/acrn.h >> > index a2d4aea3a80d..23a93b87edeb 100644 >> > --- a/arch/x86/include/asm/acrn.h >> > +++ b/arch/x86/include/asm/acrn.h >> > @@ -14,4 +14,61 @@ void acrn_setup_intr_handler(void (*handler)(void)); >> > void acrn_remove_intr_handler(void); >> > bool acrn_is_privileged_vm(void); >> > >> > +/* >> > + * Hypercalls for ACRN >> > + * >> > + * - VMCALL instruction is used to implement ACRN hypercalls. >> > + * - ACRN hypercall ABI: >> > + * - Hypercall number is passed in R8 register. >> > + * - Up to 2 arguments are passed in RDI, RSI. >> > + * - Return value will be placed in RAX. >> > + */ >> > +static inline long acrn_hypercall0(unsigned long hcall_id) >> > +{ >> > + register long r8 asm("r8"); >> > + long result; >> > + >> > + /* Nothing can come between the r8 assignment and the asm: */ >> > + r8 = hcall_id; >> > + asm volatile("vmcall\n\t" >> > + : "=a" (result) >> > + : "r" (r8) >> > + : ); >> >> What keeps an interrupt from happening between the r8 assignment and the >> asm: ? Dave gave a good explanation in another email. I will apply his better comment that "No other C code can come between this r8 assignment and the inline asm". >> >> Is this something that most hypercalls need to handle? I don't see >> other ones needing this type of thing, is it just because of how these >> are defined? > >Ah, the changelog above explains this. You should put that in the code >itself, as a comment, otherwise we will not know this at all in 5 >years, when gcc is changed to allow r8 access :) OK. I will copy that into code as well. Thanks shuo