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=-12.5 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 8068AC433E0 for ; Fri, 22 Jan 2021 12:51:53 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 14F7423106 for ; Fri, 22 Jan 2021 12:51:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 14F7423106 Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.72747.131011 (Exim 4.92) (envelope-from ) id 1l2vuK-0000nN-J7; Fri, 22 Jan 2021 12:51:20 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 72747.131011; Fri, 22 Jan 2021 12:51:20 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l2vuK-0000nG-G3; Fri, 22 Jan 2021 12:51:20 +0000 Received: by outflank-mailman (input) for mailman id 72747; Fri, 22 Jan 2021 12:51:20 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l2vuJ-0000nB-UJ for xen-devel@lists.xenproject.org; Fri, 22 Jan 2021 12:51:19 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 9a49f024-19f5-4613-947b-38961ac40f6c; Fri, 22 Jan 2021 12:51:18 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 742AAB27F; Fri, 22 Jan 2021 12:51:17 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 9a49f024-19f5-4613-947b-38961ac40f6c X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611319877; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=7C4Y0HpO+DiTAPofhEmCgDdeb61EaI6HdErwozgCz+8=; b=bCVqUsWjPTMVOZTAdPyc1IacVA8pBd/qUQ2qjiAb6kdmKeY3lb+N/XjKJQSHduOas529Tj HvSzCnfZHGQzFcrhB/vgzD30sie/GsG4k0YwPGSwgFGguEPi6f4KzzvEV9CpRNvON85hHu ul/4uek/IykJl+MbLHZg32SktSgleyE= Subject: Re: [PATCH v2 3/4] x86: Allow non-faulting accesses to non-emulated MSRs if policy permits this To: Boris Ostrovsky Cc: iwj@xenproject.org, wl@xen.org, anthony.perard@citrix.com, andrew.cooper3@citrix.com, roger.pau@citrix.com, jun.nakajima@intel.com, kevin.tian@intel.com, xen-devel@lists.xenproject.org References: <1611182952-9941-1-git-send-email-boris.ostrovsky@oracle.com> <1611182952-9941-4-git-send-email-boris.ostrovsky@oracle.com> From: Jan Beulich Message-ID: Date: Fri, 22 Jan 2021 13:51:17 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <1611182952-9941-4-git-send-email-boris.ostrovsky@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 20.01.2021 23:49, Boris Ostrovsky wrote: > --- a/xen/arch/x86/msr.c > +++ b/xen/arch/x86/msr.c > @@ -164,6 +164,34 @@ int init_vcpu_msr_policy(struct vcpu *v) > return 0; > } > > +/* Returns true if policy requires #GP to the guest. */ > +bool guest_unhandled_msr(const struct vcpu *v, uint32_t msr, uint64_t *val, > + bool is_write, bool is_guest_msr_access) Would you mind dropping the "_msr" infix from the last parameter's name? We're anyway aware we're talking about MSR accesses here, from the function name. As a nit - while I'm okay with the uint64_t *, I think the uint32_t would better be unsigned int - see ./CODING_STYLE. Finally, this being a policy function and policy being per- domain here, I think the first parameter wants to be const struct domain *. > +{ > + u8 ignore_msrs = v->domain->arch.msr->ignore_msrs; uint8_t please or, as per above, even better unsigned int. > + > + /* > + * Accesses to unimplemented MSRs as part of emulation of instructions > + * other than guest's RDMSR/WRMSR should never succeed. > + */ > + if ( !is_guest_msr_access ) > + ignore_msrs = MSR_UNHANDLED_NEVER; Wouldn't you better "return true" here? Such accesses also shouldn't be logged imo (albeit I agree that's a change from current behavior). > + if ( unlikely(ignore_msrs != MSR_UNHANDLED_NEVER) ) > + *val = 0; I don't understand the conditional here, even more so with the respective changelog entry. In any event you don't want to clobber the value ahead of ... > + if ( likely(ignore_msrs != MSR_UNHANDLED_SILENT) ) > + { > + if ( is_write ) > + gdprintk(XENLOG_WARNING, "WRMSR 0x%08x val 0x%016"PRIx64 > + " unimplemented\n", msr, *val); ... logging it. > --- a/xen/arch/x86/x86_emulate/x86_emulate.h > +++ b/xen/arch/x86/x86_emulate/x86_emulate.h > @@ -850,4 +850,10 @@ static inline void x86_emul_reset_event(struct x86_emulate_ctxt *ctxt) > ctxt->event = (struct x86_event){}; > } > > +static inline bool x86_emul_guest_msr_access(struct x86_emulate_ctxt *ctxt) The parameter wants to be pointer-to-const. In addition I wonder whether this wouldn't better be a sibling to x86_insn_is_cr_access() (without a "state" parameter, which would be unused and unavailable to the callers), which may end up finding further uses down the road. > +{ > + return ctxt->opcode == X86EMUL_OPC(0x0f, 0x32) || /* RDMSR */ > + ctxt->opcode == X86EMUL_OPC(0x0f, 0x30); /* WRMSR */ > +} Personally I'd prefer if this was a single comparison: return (ctxt->opcode | 2) == X86EMUL_OPC(0x0f, 0x32); But maybe nowadays' compilers are capable of this transformation? I notice you use this function only from PV priv-op emulation. What about the call paths through hvmemul_{read,write}_msr()? (It's also questionable whether the write paths need this - the only MSR written outside of WRMSR emulation is MSR_SHADOW_GS_BASE, which can't possibly reach the "unhandled" logic anywhere. But maybe better to be future proof here in case new MSR writes appear in the emulator, down the road.) Jan