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=-5.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS 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 3BA13C32750 for ; Fri, 2 Aug 2019 04:00:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 086F5206A3 for ; Fri, 2 Aug 2019 04:00:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=brainfault-org.20150623.gappssmtp.com header.i=@brainfault-org.20150623.gappssmtp.com header.b="RJKKjy4l" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726052AbfHBEAN (ORCPT ); Fri, 2 Aug 2019 00:00:13 -0400 Received: from mail-wm1-f67.google.com ([209.85.128.67]:37120 "EHLO mail-wm1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725385AbfHBEAN (ORCPT ); Fri, 2 Aug 2019 00:00:13 -0400 Received: by mail-wm1-f67.google.com with SMTP id f17so64950540wme.2 for ; Thu, 01 Aug 2019 21:00:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=brainfault-org.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=I/Kfc6ZbOZnKoxJL7rV1rbyTQYfEjNQbR94dlPzKkok=; b=RJKKjy4lH/3bgMCwOjm1J18wa06vOSJLnIfHMmvULIy2YSHW3G15WM/m7+XeVtQwTr UtiihTcbvICV40K4Nt5x73lPEsV6pBUGS2RPKA5G47fKyoSSsc05AlAuvBSyjU7yAX3Z UoEhsAOtv282G86OCYcLO5YN8helw4/uL1qOeUEBiTmpuinXLeVN3veX4kAGMwHIkC65 EKZaEk2RjAR5n1/oURiPuFkOL29Vt+pAgswdD0zpyPv3xy2fYhEiWrtIozD6TCcfhHcV OMLP1cmi5mf327NBxa+CEE9sTtQnunCR/GUerMu62fmDkaROt4YIFVsA2qWBl2CNKsLY 7Dvw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=I/Kfc6ZbOZnKoxJL7rV1rbyTQYfEjNQbR94dlPzKkok=; b=gOOPrrJHAmCnA6XLl+6Qrc67kVSD4C0mBJ3FR8Wfwi4WkVCLrwZKH3dhUAqIHhRryb okZVbJKegmaImk8IOiJCyruFsAFoga0Syt5F46AgvoRbMkzrYIRDnKCbQMrTEtqwoh/D S5wMq2244gvWDziO+eTkqMsUR5ssaYl0lbOw8sktgWkyCQbWreW84LNEPm7zhwJSi8OV PqASMFefSkzQtYexl9XkUw4V81fSV+6iwr2voJ9nybtOwp/Zml81q8KqdfmZT7npvnqn ltMp94eX85sNskw7oNZLhKS/7ozCgwr5wl6H7h29tRUwdaHhuPm2+5qGs5zEjStSVEGc DrNQ== X-Gm-Message-State: APjAAAVkstULgjPZH/zj1CnoZtJtoYq+8p2wWTDyPlttnYad9jtOO5Pt q3IBir6mFtI/EUS32xgOg3cG0i0If7n91k6+/6gn8A== X-Google-Smtp-Source: APXvYqyGKKA06Ook1nC1Ms5baz5sFRFDqfDRQkOGCbnR8q7MWD+Cy/I3+JJpDuoiot2nNz8c8O4OOUXtH5DkcbO6xGI= X-Received: by 2002:a1c:cfc5:: with SMTP id f188mr1649160wmg.24.1564718409992; Thu, 01 Aug 2019 21:00:09 -0700 (PDT) MIME-Version: 1.0 References: <20190729115544.17895-1-anup.patel@wdc.com> <20190729115544.17895-6-anup.patel@wdc.com> <9f9d09e5-49bc-f8e3-cfe1-bd5221e3b683@redhat.com> <66c4e468-7a69-31e7-778b-228908f0e737@redhat.com> <828f01a9-2f11-34b6-7753-dc8fa7aa0d18@redhat.com> <816c70e7-0ea3-1dde-510e-f1d5c6a02dd5@redhat.com> In-Reply-To: <816c70e7-0ea3-1dde-510e-f1d5c6a02dd5@redhat.com> From: Anup Patel Date: Fri, 2 Aug 2019 09:29:59 +0530 Message-ID: Subject: Re: [RFC PATCH 05/16] RISC-V: KVM: Implement VCPU interrupts and requests handling To: Paolo Bonzini Cc: Anup Patel , Palmer Dabbelt , Paul Walmsley , Radim K , Daniel Lezcano , Thomas Gleixner , Atish Patra , Alistair Francis , Damien Le Moal , Christoph Hellwig , "kvm@vger.kernel.org" , "linux-riscv@lists.infradead.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Tue, Jul 30, 2019 at 7:38 PM Paolo Bonzini wrote: > > On 30/07/19 15:35, Anup Patel wrote: > > On Tue, Jul 30, 2019 at 6:48 PM Paolo Bonzini wrote: > >> > >> On 30/07/19 14:45, Anup Patel wrote: > >>> Here's some text from RISC-V spec regarding SIP CSR: > >>> "software interrupt-pending (SSIP) bit in the sip register. A pending > >>> supervisor-level software interrupt can be cleared by writing 0 to the SSIP bit > >>> in sip. Supervisor-level software interrupts are disabled when the SSIE bit in > >>> the sie register is clear." > >>> > >>> Without RISC-V hypervisor extension, the SIP is essentially a restricted > >>> view of MIP CSR. Also as-per above, S-mode SW can only write 0 to SSIP > >>> bit in SIP CSR whereas it can only be set by M-mode SW or some HW > >>> mechanism (such as S-mode CLINT). > >> > >> But that's not what the spec says. It just says (just before the > >> sentence you quoted): > >> > >> A supervisor-level software interrupt is triggered on the current > >> hart by writing 1 to its supervisor software interrupt-pending (SSIP) > >> bit in the sip register. > > > > Unfortunately, this statement does not state who is allowed to write 1 > > in SIP.SSIP bit. > > If it doesn't state who is allowed to write 1, whoever has access to sip > can. > > > I quoted MIP CSR documentation to highlight the fact that only M-mode > > SW can set SSIP bit. > > > > In fact, I had same understanding as you have regarding SSIP bit > > until we had MSIP issue in OpenSBI. > > (https://github.com/riscv/opensbi/issues/128) > > > >> and it's not written anywhere that S-mode SW cannot write 1. In fact > >> that text is even under sip, not under mip, so IMO there's no doubt that > >> S-mode SW _can_ write 1, and the hypervisor must operate accordingly. > > > > Without hypervisor support, SIP CSR is nothing but a restricted view of > > MIP CSR thats why MIP CSR documentation applies here. > > But the privileged spec says mip.MSIP is read-only, it cannot be cleared > (as in the above OpenSBI issue). So mip.MSIP and sip.SSIP are already > different in that respect, and I don't see how the spec says that S-mode > SW cannot set sip.SSIP. > > (As an aside, why would M-mode even bother using sip and not mip to > write 1 to SSIP?). > > > I think this discussion deserves a Github issue on RISC-V ISA manual. > > Perhaps, but I think it makes more sense this way. The question remains > of why M-mode is not allowed to write to MSIP/MEIP/MTIP. My guess is > that then MSIP/MEIP/MTIP are simply a read-only view of an external pin, > so it simplifies hardware a tiny bit by forcing acks to go through the > MMIO registers. > > > If my interpretation is incorrect then it would be really strange that > > HART in S-mode SW can inject IPI to itself by writing 1 to SIP.SSIP bit. > > Well, it can be useful, for example Windows does it when interrupt > handlers want to schedule some work to happen out of interrupt context. > Going through SBI would be unpleasant if it causes an HS-mode trap. Another way of artificially injecting interrupt would be using interrupt controller, where Windows can just write to some pending register of interrupt controller. I have raised a new Github issue on GitHub for clarity on this. You can add your comments to this issue as well. https://github.com/riscv/riscv-isa-manual/issues/425 Also, I have raised a proposal to support mechanism for external entity (such as PLICv2 with virtualization support) to inject virtual interrupts. https://github.com/riscv/riscv-isa-manual/issues/429 Regards, Anup