From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [PATCH] Re: I/O port access handling for PVH Date: Mon, 2 Dec 2013 11:31:02 +0000 Message-ID: <529C6F76.5050205@eu.citrix.com> References: <526551DE02000078000FC6FD@nat28.tlf.novell.com> <20131128110108.GD36239@deinos.phlegethon.org> <52972AFA.3010506@eu.citrix.com> <20131128114401.GG36239@deinos.phlegethon.org> <52986A150200007800108111@nat28.tlf.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta3.messagelabs.com ([195.245.230.39]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1VnRiX-0008Au-Hj for xen-devel@lists.xenproject.org; Mon, 02 Dec 2013 11:31:09 +0000 In-Reply-To: <52986A150200007800108111@nat28.tlf.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich , Tim Deegan Cc: xen-devel , Boris Ostrovsky , Suravee Suthikulpanit List-Id: xen-devel@lists.xenproject.org On 11/29/2013 09:19 AM, Jan Beulich wrote: >>>> On 28.11.13 at 12:44, Tim Deegan wrote: >> At 11:37 +0000 on 28 Nov (1385635050), George Dunlap wrote: >>> On 11/28/2013 11:01 AM, Tim Deegan wrote: >>>> At 15:10 +0100 on 21 Oct (1382364606), Jan Beulich wrote: >>>>> In particular it would then hopefully be safe to do all that without >>>>> the on-stack emulation stub, as this ought to be necessary only >>>>> for Dom0, which ought to always have direct access to such >>>>> "special" I/O ports. With one apparent caveat: SVM sets >>>>> GENERAL1_INTERCEPT_SMI (for a reason that escapes my right >>>>> now), and hence control doesn't transfer directly to SMM when >>>>> an SMI occurs (and consequently registers aren't expected). But >>>>> I would hope that this intercept isn't really needed, and hence >>>>> could be dropped at least for PVH guests. >>>> (I realise I'm rather late replying to this - I put it aside and then >>>> only found it again today) >>>> >>>> On machines where the BIOS has locked down SMM mode, this >>>> intercept is in fact ignored by the hardware, and that works fine. >>>> So we can drop it for all VMs if it's convenient: >>>> >>>> commit a842864f3901078e2a5f4d1cca2f01a72c8d7d13 >>>> Author: Tim Deegan >>>> Date: Thu Nov 28 10:58:42 2013 +0000 >>>> >>>> x86/svm: don't intercept SMI. >>>> >>>> The SMI intercept is ignored anyway when the BIOS has set the SMMLOCK >>>> bit in HWCR (see APM v3.21, volume 2, 15.13.3) and it's convenient for >>>> PVH IO processing to have the SMI handled directly with the guest's >>>> GPR state (for BIOSes that use SMI as a sort of function call >> interface). >>>> >>>> Signed-off-by: Tim Deegan >>> I take it you're not targeting this for 4.4? >> Indeed not. Sorry, I should have said so. > And even more so considering that PVH support on SVM is going > to remain a todo item for after 4.4 anyway. Yes, I had started to write this, but figured there was no point discussing the merits of accepting it if Tim wasn't asking for it to be accepted. :-) -George