From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B168471 for ; Wed, 19 May 2021 17:56:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=0VusAJZ3GsBzVSdLTEAGWr7rdRHdzn/JtH42moT3IVU=; b=RF8RFvqQuOtdFP/lCsk93yjuz9 LTOSQBYY2k6m3umvaeS2K30f9je5U14s6FuCQezx+ml8LwzduT3682kYN72e7kAXxlFkaLpCEkALU u9NL1h1C4e/riHeHEUZfm16LDlc3uHlsIRFrZPWeixuho32kANI9e+dZzxJNM9siit0/n4Jmxmcli 5kONPHTxaJ+tC/1VAo5uRnYbKWhHetXqeNRAzaShstYsNAvCqs+n7znoLP1qSotPo+nM0EN3S7Mgq Gz/lXNIqTq6iNQCjCe/BNG6yKXdM2Kr0aOI7y0Z+cWo2vI4JH67DZTB/1qxgdQ87QkyaDvmBMEUjR XP02rlpA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1ljQPD-00FB8B-O6; Wed, 19 May 2021 17:55:03 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 336EF986465; Wed, 19 May 2021 19:54:50 +0200 (CEST) Date: Wed, 19 May 2021 19:54:50 +0200 From: Peter Zijlstra To: Joerg Roedel Cc: x86@kernel.org, Hyunwook Baek , Joerg Roedel , hpa@zytor.com, Andy Lutomirski , Dave Hansen , Jiri Slaby , Dan Williams , Tom Lendacky , Juergen Gross , Kees Cook , David Rientjes , Cfir Cohen , Erdem Aktas , Masami Hiramatsu , Mike Stunes , Sean Christopherson , Martin Radev , Arvind Sankar , linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v2 5/8] x86/sev-es: Leave NMI-mode before sending signals Message-ID: <20210519175450.GF21560@worktop.programming.kicks-ass.net> References: <20210519135251.30093-1-joro@8bytes.org> <20210519135251.30093-6-joro@8bytes.org> X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210519135251.30093-6-joro@8bytes.org> On Wed, May 19, 2021 at 03:52:48PM +0200, Joerg Roedel wrote: > --- a/arch/x86/kernel/sev.c > +++ b/arch/x86/kernel/sev.c > @@ -1343,9 +1343,10 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication) > return; > } > > + instrumentation_begin(); > + > irq_state = irqentry_nmi_enter(regs); > lockdep_assert_irqs_disabled(); > - instrumentation_begin(); > > /* > * This is invoked through an interrupt gate, so IRQs are disabled. The That's just plain wrong. No instrumentation is allowed before you enter the exception context. > @@ -1395,13 +1396,19 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication) > BUG(); > } > > -out: > - instrumentation_end(); > irqentry_nmi_exit(regs, irq_state); > + instrumentation_end(); And this can't be right either, same issue, no instrumentation is allowed after you leave the exception context. > > return; > > fail: > + /* > + * Leave NMI mode - the GHCB is not busy anymore and depending on where > + * the #VC came from this code is about to either kill the task (when in > + * task context) or kill the machine. > + */ > + irqentry_nmi_exit(regs, irq_state); > + And this is wrong too; because at this point the handler doesn't run in _any_ context anymore, certainly not one you can call regular C code from. > if (user_mode(regs)) { > /* > * Do not kill the machine if user-space triggered the > @@ -1423,7 +1430,9 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication) > panic("Returned from Terminate-Request to Hypervisor\n"); > } > > - goto out; > + instrumentation_end(); > + > + return; > } You either get to do what MCE does, or what MCE does. That is, either use task_work or MCE_USER and have the _user() handler use irqentry_enter_from_user_mode(). The above is an absolute no-go. 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Wed, 19 May 2021 17:56:40 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Authentication-Results: smtp2.osuosl.org (amavisd-new); dkim=pass (2048-bit key) header.d=infradead.org Received: from smtp2.osuosl.org ([127.0.0.1]) by localhost (smtp2.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id qEoY0SjcPAa3 for ; Wed, 19 May 2021 17:56:37 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.8.0 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by smtp2.osuosl.org (Postfix) with ESMTPS id C38C3403ED for ; Wed, 19 May 2021 17:56:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=0VusAJZ3GsBzVSdLTEAGWr7rdRHdzn/JtH42moT3IVU=; b=RF8RFvqQuOtdFP/lCsk93yjuz9 LTOSQBYY2k6m3umvaeS2K30f9je5U14s6FuCQezx+ml8LwzduT3682kYN72e7kAXxlFkaLpCEkALU u9NL1h1C4e/riHeHEUZfm16LDlc3uHlsIRFrZPWeixuho32kANI9e+dZzxJNM9siit0/n4Jmxmcli 5kONPHTxaJ+tC/1VAo5uRnYbKWhHetXqeNRAzaShstYsNAvCqs+n7znoLP1qSotPo+nM0EN3S7Mgq Gz/lXNIqTq6iNQCjCe/BNG6yKXdM2Kr0aOI7y0Z+cWo2vI4JH67DZTB/1qxgdQ87QkyaDvmBMEUjR XP02rlpA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1ljQPD-00FB8B-O6; Wed, 19 May 2021 17:55:03 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 336EF986465; Wed, 19 May 2021 19:54:50 +0200 (CEST) Date: Wed, 19 May 2021 19:54:50 +0200 From: Peter Zijlstra To: Joerg Roedel Subject: Re: [PATCH v2 5/8] x86/sev-es: Leave NMI-mode before sending signals Message-ID: <20210519175450.GF21560@worktop.programming.kicks-ass.net> References: <20210519135251.30093-1-joro@8bytes.org> <20210519135251.30093-6-joro@8bytes.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210519135251.30093-6-joro@8bytes.org> Cc: kvm@vger.kernel.org, Dave Hansen , virtualization@lists.linux-foundation.org, Arvind Sankar , hpa@zytor.com, Jiri Slaby , x86@kernel.org, David Rientjes , Martin Radev , Tom Lendacky , Joerg Roedel , Kees Cook , Cfir Cohen , Hyunwook Baek , linux-coco@lists.linux.dev, Andy Lutomirski , Dan Williams , Juergen Gross , Mike Stunes , Sean Christopherson , linux-kernel@vger.kernel.org, Masami Hiramatsu , Erdem Aktas X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Wed, May 19, 2021 at 03:52:48PM +0200, Joerg Roedel wrote: > --- a/arch/x86/kernel/sev.c > +++ b/arch/x86/kernel/sev.c > @@ -1343,9 +1343,10 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication) > return; > } > > + instrumentation_begin(); > + > irq_state = irqentry_nmi_enter(regs); > lockdep_assert_irqs_disabled(); > - instrumentation_begin(); > > /* > * This is invoked through an interrupt gate, so IRQs are disabled. The That's just plain wrong. No instrumentation is allowed before you enter the exception context. > @@ -1395,13 +1396,19 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication) > BUG(); > } > > -out: > - instrumentation_end(); > irqentry_nmi_exit(regs, irq_state); > + instrumentation_end(); And this can't be right either, same issue, no instrumentation is allowed after you leave the exception context. > > return; > > fail: > + /* > + * Leave NMI mode - the GHCB is not busy anymore and depending on where > + * the #VC came from this code is about to either kill the task (when in > + * task context) or kill the machine. > + */ > + irqentry_nmi_exit(regs, irq_state); > + And this is wrong too; because at this point the handler doesn't run in _any_ context anymore, certainly not one you can call regular C code from. > if (user_mode(regs)) { > /* > * Do not kill the machine if user-space triggered the > @@ -1423,7 +1430,9 @@ DEFINE_IDTENTRY_VC_SAFE_STACK(exc_vmm_communication) > panic("Returned from Terminate-Request to Hypervisor\n"); > } > > - goto out; > + instrumentation_end(); > + > + return; > } You either get to do what MCE does, or what MCE does. That is, either use task_work or MCE_USER and have the _user() handler use irqentry_enter_from_user_mode(). The above is an absolute no-go. _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization