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=-14.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 981A7C43461 for ; Wed, 16 Sep 2020 00:57:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5CA80207DE for ; Wed, 16 Sep 2020 00:57:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600217831; bh=L4IN4jrJMrOqlZS6N6dXZnpcEQv+lcdLEvEOv+9U5bg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ReL/mSvBmA1ci5pdEk9iBbi4QIbVf1e9FOjoYIy8ufp+W2gsWorO6ZcrdcF0tkEI7 C2TxqSbXM2+7d3k9NyUok1qyLtZEl53wHtr37Nv1AYJdWRGh2R6sAB5rIMGtjwidHq tTZUPJA+TrztsjctnWgltAqVeylw6C6ghnPREAjw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726383AbgIPA5H (ORCPT ); Tue, 15 Sep 2020 20:57:07 -0400 Received: from mail-wm1-f65.google.com ([209.85.128.65]:37872 "EHLO mail-wm1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726028AbgIOLRD (ORCPT ); Tue, 15 Sep 2020 07:17:03 -0400 Received: by mail-wm1-f65.google.com with SMTP id a9so3051504wmm.2; Tue, 15 Sep 2020 04:17:00 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=hOrViQ9/e7YRFhxWzh4oAfdg10S4Mh+sHS2iw3u+aPQ=; b=Sn+90mqdrU3QNPs9sCDrTwjeYVTmKMofrzI+RIKaz9eiHrHnwJjsyFasSSQRILRK8B ioB8n6jXQ/fGWzwJO74JCQOJhzsINgdI1H6vcrnLdsxnXGbmf3xIOYhZOPWEHcotn9Aw l1hBP9H4JVN/nHUJNMkedTM+S/bfHbpdSC3YCaov+BTcBhpo3FP/fxYgHIWa12dtDm9w xQ5O353iJwEjbSi1dBkH5M+6cP+j76NaksOoUI8VDR9aKpTgAzJfBtzR3ThsxhFGAUej rCMfn7ssa2vPWIbgru3cqexlrUx7yu863vNwEc59tweqh3nZ9WVNoNQPp53ZS4g04pOv l3WQ== X-Gm-Message-State: AOAM5326B+RyJffM6299jZjAIm9oI8mo6GJ8p/QRChDMyip18eTDfTOl vLdgqBY7KZN237VrEQ4xzLo= X-Google-Smtp-Source: ABdhPJy1VFDORM4UB6MEbKPiZ2llP2YFkYLjd3Qs0Ww2nBtbDj7mZyIoMjLtJ6m0v1k2oL4yvXavKw== X-Received: by 2002:a7b:cc88:: with SMTP id p8mr4221626wma.150.1600168619567; Tue, 15 Sep 2020 04:16:59 -0700 (PDT) Received: from liuwe-devbox-debian-v2 ([51.145.34.42]) by smtp.gmail.com with ESMTPSA id 197sm25213904wme.10.2020.09.15.04.16.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2020 04:16:59 -0700 (PDT) Date: Tue, 15 Sep 2020 11:16:57 +0000 From: Wei Liu To: Vitaly Kuznetsov Cc: Wei Liu , Linux on Hyper-V List , virtualization@lists.linux-foundation.org, Linux Kernel List , Michael Kelley , Vineeth Pillai , Sunil Muthuswamy , Nuno Das Neves , Lillian Grassin-Drake , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "H. Peter Anvin" Subject: Re: [PATCH RFC v1 08/18] x86/hyperv: handling hypercall page setup for root Message-ID: <20200915111657.boa4cneqjqtmcaaq@liuwe-devbox-debian-v2> References: <20200914112802.80611-1-wei.liu@kernel.org> <20200914112802.80611-9-wei.liu@kernel.org> <87v9gfjpoi.fsf@vitty.brq.redhat.com> <20200915103710.cqmdvzh5lys4wsqo@liuwe-devbox-debian-v2> <87pn6njob3.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87pn6njob3.fsf@vitty.brq.redhat.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 15, 2020 at 01:02:08PM +0200, Vitaly Kuznetsov wrote: > Wei Liu writes: > > > On Tue, Sep 15, 2020 at 12:32:29PM +0200, Vitaly Kuznetsov wrote: > >> Wei Liu writes: > >> > >> > When Linux is running as the root partition, the hypercall page will > >> > have already been setup by Hyper-V. Copy the content over to the > >> > allocated page. > >> > >> And we can't setup a new hypercall page by writing something different > >> to HV_X64_MSR_HYPERCALL, right? > >> > > > > My understanding is that we can't, but Sunil can maybe correct me. > > > >> > > >> > The suspend, resume and cleanup paths remain untouched because they are > >> > not supported in this setup yet. > >> > > >> > Signed-off-by: Lillian Grassin-Drake > >> > Signed-off-by: Sunil Muthuswamy > >> > Signed-off-by: Nuno Das Neves > >> > Co-Developed-by: Lillian Grassin-Drake > >> > Co-Developed-by: Sunil Muthuswamy > >> > Co-Developed-by: Nuno Das Neves > >> > Signed-off-by: Wei Liu > >> > --- > >> > arch/x86/hyperv/hv_init.c | 26 ++++++++++++++++++++++++-- > >> > 1 file changed, 24 insertions(+), 2 deletions(-) > >> > > >> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c > >> > index 0eec1ed32023..26233aebc86c 100644 > >> > --- a/arch/x86/hyperv/hv_init.c > >> > +++ b/arch/x86/hyperv/hv_init.c > >> > @@ -25,6 +25,7 @@ > >> > #include > >> > #include > >> > #include > >> > +#include > >> > > >> > /* Is Linux running as the root partition? */ > >> > bool hv_root_partition; > >> > @@ -448,8 +449,29 @@ void __init hyperv_init(void) > >> > > >> > rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64); > >> > hypercall_msr.enable = 1; > >> > - hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg); > >> > - wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64); > >> > + > >> > + if (hv_root_partition) { > >> > + struct page *pg; > >> > + void *src, *dst; > >> > + > >> > + /* > >> > + * Order is important here. We must enable the hypercall page > >> > + * so it is populated with code, then copy the code to an > >> > + * executable page. > >> > + */ > >> > + wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64); > >> > + > >> > + pg = vmalloc_to_page(hv_hypercall_pg); > >> > + dst = kmap(pg); > >> > + src = memremap(hypercall_msr.guest_physical_address << PAGE_SHIFT, PAGE_SIZE, > >> > + MEMREMAP_WB); > >> > >> memremap() can fail... > > > > And we don't care here, if it fails, we would rather it panic or oops. > > > > I was relying on the fact that copying from / to a NULL pointer will > > cause the kernel to crash. But of course it wouldn't hurt to explicitly > > panic here. > > > >> > >> > + memcpy(dst, src, PAGE_SIZE); > >> > + memunmap(src); > >> > + kunmap(pg); > >> > + } else { > >> > + hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg); > >> > + wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64); > >> > + } > >> > >> Why can't we do wrmsrl() for both cases here? > >> > > > > Because the hypercall page has already been set up when Linux is the > > root. > > But you already do wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64) > in 'if (hv_root_partition)' case above, that's why I asked. > You mean extracting wrmsrl to this point? The ordering matters. See the comment in the root branch -- we have to enable the page before copying the content. What can be done is: if (!root) { /* some stuff */ } wrmsrl(...) if (root) { /* some stuff */ } This is not looking any better than the existing code. Wei. > > > > I could've tried writing to the MSR again, but because the behaviour > > here is not documented and subject to change so I didn't bother trying. > > > > Wei. > > > >> > > >> > /* > >> > * Ignore any errors in setting up stimer clockevents > >> > >> -- > >> Vitaly > >> > > > > -- > Vitaly >